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Axis determination

Learn how to determine the QRS axis on an ECG and why.

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Axis determination

  1. 1. Axis Determination Thompson 2 Resources
  2. 2. Axis Determination Thompson 3
  3. 3. Axis Determination Thompson 4 PathologiesMany different conditions cause axis deviation. Being able to determine whether axis deviation exists, and to whatextent can assist in the interpretation of the 12-lead ECG. This is a commonly overlooked skill that can aid inassessment and proper treatment. The next few pages are from
  4. 4. Axis Determination Thompson 5 Why should you learn how to determine the electrical axis? By Tom BouthiletThe most common causes of left axis deviation are left anterior fascicular block and Q-waves from inferior MI. So whenI see a left axis deviation it prompts me to consider these conditions. Many times I have caught subtle inferior STEMIsbecause the axis was slightly to the left and it prompted me to look at lead aVL for subtle reciprocal changes.
  5. 5. Axis Determination Thompson 6A paced rhythm with a pacing lead in the apex of the right ventricle typically shows LBBB morphology in lead V1 and leftaxis deviation. So this prompts me to double-check for a pacemaker pocket on the patient’s chest and consider that therhythm may be paced before I decide the patient is showing frequent PVCs or a run of slow VT.
  6. 6. Axis Determination Thompson 7Conversely, it would be very unusual for LBBB or paced rhythm to show LBBB moprhology in lead V1 with a right axisdeviation. That in turn further supports the dx of VT in a patient who happens to have a pacemaker. That helped meidentify a run of VT at a rate of 140 when others called it a “runaway pacemaker.”
  7. 7. Axis Determination Thompson 8A pulmonary disease pattern may pull the axis to the right. It may also cause right atrial enlargement. In addition manycongenital heart defects cause right ventricular hypertrophy with an associated right ventricular strain pattern. So whenyou see right axis deviation, tall R-waves in lead V1, and T-wave inversion in the right precordial leads, you know it’sconsistent with the patient’s history and not “anterior ischemia” requiring NTG.
  8. 8. Axis Determination Thompson 9Q-waves from high lateral MI pulls the axis to the right. Left posterior fascicular block is rare as an isolated finding, butthat also pulls the axis to the right. Combine left anterior fascicular block (left axis deviation) or left posterior fascicularblock (right axis deviation) with RBBB morphology in lead V1 and it’s referred to as a “bifascicular pattern”
  9. 9. Axis Determination Thompson 10An extreme right axis deviation (or right superior axis depending on what terminology you prefer) might suggestincorrect lead placement, electrolyte derangement, or help you rule-in a ventricular rhythm. Never assume that a widecomplex tachycardia is SVT with aberrancy based solely on QRS morphology! Just because it looks like LBBB doesn’tmean it isn’t VT.
  10. 10. Axis Determination Thompson 11 Part 1 The Frontal Plane Axis
  11. 11. Axis Determination Thompson 12 Einthoven’s Triangle Willem Einthoven won the Nobel Prize in Physiology or Medicine in 1924 for inventing the string galvanometer; which was the first EKG. Because Einthoven was German, this is why electrocardiogram is abbreviated EKG for “electrokardiogram”—the Dutch spelling.Einthoven’s arms and his left leg are immersed in buckets of salt water. At the time, this was the only way toobtain a signal for the electrocardiograph. Even after the invention of the electrode, they continued to be placed onthe subject’s arms and legs. From this configuration, leads I, II, and III were born, and they are called the limbleads to this day.
  12. 12. Axis Determination Thompson 13 Einthoven’s TriangleElectrically, leads I, II, & III form an equilateral triangle.Einthoven’s Law: I + (-II) + III = 0What is lead I? It is a dipole, with the negative electrode at the right arm (whiteelectrode) and the positive electrode at the left arm (black electrode).What is lead III? It is a dipole with the negative electrode at the left arm (blackelectrode) and the positive electrode at the left leg (red electrode).Confused? It gets easier!
  13. 13. Axis Determination Thompson 14 Einthoven’s TriangleHow it works:- First take a look at Lead I. The R wave is about 7 1/2 mm tall. The S wave isabout 2 1/2 mm deep. Subtract the S wave from the R wave, and you come up with5 mm. 7.5 – 2.5 = 5- Lead II is essentially monophasic (only goes in one direction—down). So subtractthe depth of the S-wave from zero. 0 – 10 = -10- Lead III has an R-wave of about 1mm and an S-wave about 16mm. Subtract theS-wave from the R-wave. 1 – 16 = -15Lead I = 5mmLead II = -10mmLead III = -15mmPlug the numbers in.  I + (-II) + III = 0  5 + 10 -15 = 0
  14. 14. Axis Determination Thompson 15 Einthoven’s TriangleAs you can see, when you plug in themeasurements, you end up with an electricalvalue of zero. You can try this trick onvirtually any ECG. Because this is true,leads I, II, and III can be represented as anelectrically equilateral triangle.
  15. 15. Axis Determination Thompson 16 Electrical Axis This diagram shows the sequence of ventricular depolarization. As you can see, the first area to depolarize (1) is the interventricular septum, which depolarizes in a left-to-right direction (responsible for the so-called septal Q waves in the lateral leads of a normal 12 lead ECG). - The first area to depolarize (1) is the interventricular septum. - Next, the area around the left and right ventricular apex (2) depolarizes from a endocardial-to-epicardial direction (inside-out). - Finally, the lateral walls of the left and right ventricle depolarize (3) and last the high lateral wall of the left ventricle (4). Now notice the large arrow superimposed over the top of the diagram. This is the heart’s “mean electrical vector”. That means if you averaged the millions of electrical vectors created as the ventricles depolarize in any given cardiac cycle, the average direction would be right-to-left.
  16. 16. Axis Determination Thompson 17 Mean Electrical Vector + + A B A + BWhen the heart’s mean electrical vector moves toward a positive electrode, you get an upright complex on the ECG in that lead.When the heart’s mean electrical vector moves away from a positive electrode, you get a negative complex on the ECG in that lead.When the heart’s mean electrical vector moves perpendicular to a positive electrode, you get a so-called equiphasic complex. It startsout positive (A) as the mean electrical vector approaches, but ends up negative (B) as the vector passes on by.
  17. 17. Axis Determination Thompson 18 Mean Electrical VectorNow let go back to Einthoven (electrically) Equilateral Triangle. Imagine that the red arrow is the heart’s mean electrical vector.In physics, two vectors (or in this case leads) are equal as long as they are parallel and of the same intensity and polarity. Therefore,we can move the leads to a point passing through the center of the heart, and they will be the same.
  18. 18. Axis Determination Thompson 19 Hexaxial Reference SystemBecause this is true, we can take the three vectors (or sides) of Einthoven’s Triangle and make them intersect in the center. This is thefirst step in creating our hexaxial reference system.
  19. 19. Axis Determination Thompson 20 Hexaxial Reference System We examined how Einthoven was able to refer to leads I, II, and III as Einthoven’s Equilateral Triangle. For the exact same reasons, we can draw a mathematical representation of leads aVR, aVL, and aVF that looks symmetrical like the shape above.
  20. 20. Axis Determination Thompson 21The arrows and lead names are placed on the side of the positive electrode. We will be using the Hexaxial Reference System todetermine the mean electrical axis of the 12-lead ECGs.After learning the Hexaxial Reference System way of determining the mean electrical axis in the frontal plane, we will review aneasier method of obtaining a quick estimate of the hearts electrical axis.Imagine that the intersection of all those lines is directly in the center of the heart. This explains which area of the heart the leads arelooking at.
  21. 21. Axis Determination Thompson 22Before we break down the finished diagram, let’s look at the hexaxial reference system layingon top of the patient’s anterior chest, with the arrows and leads in the position of the positiveelectrodes. The first thing I would like you to notice is that lead I cuts the body in halfhorizontally and lead aVF cuts the body in half vertically.The second thing I would like you to notice is that even though leads II, III, and aVF share thesame positive electrode, they represent three separate vectors. This diagram should clearlydemonstrate why we call them the inferior leads. It should also demonstrate why we call leadsI and aVL the high lateral leads.You will notice that leads III and aVL are on opposite sides of the hexaxial reference system.That’s why they are two of the most reciprocal leads on the 12 lead ECG. You will notice thatlead II cuts across the body in a right shoulder-to-left leg direction (white electrode to redelectrode); which is the same direction as the heart’s normal axis. That’s probably why wewere first taught to monitor lead II. It tends to show nice, upright P waves, QRS complexes,and T waves.
  22. 22. Axis Determination Thompson 23 Hexaxial Method 5 Easy Steps Step 1: Determine the equiphasic lead. Step 2: Find that lead on the diagram. Step 3: Find the perpendicular lead. Step 4: Determine if it is positive or negative. Step 5: Find your Axis. The Hexaxial Method will determine the mean QRS axis in the frontal plane. The conclusion will be within 15 degrees of the exact axis.
  23. 23. Axis Determination Thompson 24Using the Hexaxial Reference System:ECG - 1For now, we will concentrate only on the first six leads of the 12-lead ECG. These leads make up the frontal plane. We will be usingthe Hexaxial Reference System to determine our mean electrical axis in the frontal plane.
  24. 24. Axis Determination Thompson 25Step 1: Find the most equiphasic leadECG - 1 Step 1The first step in determining the heart’s mean electrical axis in the frontal plane is to find the most equiphasic lead –this basicallymeans find the lead with QRS complexes that are equally positive & negative.aVL in ECG – 1 has very small QRS complexes. The smaller a QRS complex is, the more equiphasic it is. The R-wave seems to beequally as tall as the S-wave is deep.
  25. 25. Axis Determination Thompson 26 + + A B A + BRemember. When the heart’s mean electrical vector (or QRS axis) moves toward a positive electrode, you get an upright complex inthat lead. When it moves away from a positive electrode, you get a negative complex in that lead. When it moves perpendicular to apositive electrode, you get an equiphasic (and/or isoelectric) complex in that lead.Since we know that, we can say that on ECG – 1, our mean electrical axis is perpendicular to aVL.
  26. 26. Axis Determination Thompson 27Step 2: Find the equiphasic lead on the Hexaxial Reference System.Step 3: Find the lead perpendicular to the equiphasic lead. Step 2 Step 3We stated that ECG – 1 shows aVL as the most equiphasic lead. Lead II appears to be perpendicular to aVL. Since we know that aVLis perpendicular to our QRS axis (mean electrical axis), and lead II is perpendicular to aVL, we can conclude that lead II is inline withthe QRS axis of ECG -1. If you look at lead II on the Hexaxial Reference System, you will see a different number on either end, +60& -120. The QRS axis is either 60 or -120.
  27. 27. Axis Determination Thompson 28Step 4: Determine if your inline lead is positive or negative.ECG - 1 Step 4Lead II is obviously positive.*Notice how lead II has the largest QRS complexes out of the first six leads? This is evidence that we are correct in concluding thatlead II is the most inline lead with the QRS axis**In case you were wondering, this ECG is a Lateral Wall STEMI, with ST-Elevation in V5, V6, I, & aVL.
  28. 28. Axis Determination Thompson 29Step 5: Match your findings to your diagram Step 5Since lead II is positive, the side with the up arrow next to theRoman numeral is the side with our axis.The diagram shows + 60º on the positive side of lead II. Thismeans that our QRS axis is around 60º (give or take 15º).The normal QRS axis is from 0º to 90ºThink about what that means. It means that if you average all the directions of travel that the electricity in the heart takes duringventricular depolarization, you would see that the impulse is mostly traveling towards the positive electrode of lead II; which isnormal. This doesn’t mean that the patient isn’t having a cardiac issue, just that their QRS axis is normal.
  29. 29. Axis Determination Thompson 30 Normal AxisSouthEast QuadrantRemember that the normal QRS axis goes from a right shoulder-to-left leg direction in most patients. In other words, it tends to pointdown and to the left, or toward the left inferior quadrant of thehexaxial reference system, which ranges from 0 to +90 degrees.When the QRS axis in the frontal plane is in the normal quadrant, youwill have positive QRS complexes in lead I and positive QRScomplexes in lead aVF.
  30. 30. Axis Determination Thompson 31 Left Axis DeviationNorthEast QuadrantWhen the QRS axis is 0 to -90 degrees, we call it a left axis deviation.This is the left superior quadrant of the hexaxial reference system. Whenthe QRS axis is in the left superior quadrant, you will have positive QRScomplexes in lead I and negative QRS complexes in lead aVF.From 0° to -30° is considered physiological left axis deviation.Pathological left axis deviation is from -30° to -90°.Most common cause is left anterior fascicular block (LAFB).
  31. 31. Axis Determination Thompson 32 Right Axis DeviationSouthWest QuadrantIf the QRS axis in the frontal plane is +90 to 180 degrees, it is a right axisdeviation. This is the right inferior quadrant of the hexaxial referencesystem. With a right axis deviation, you will have negative QRS complexesin lead I and positive QRS complexes in lead aVF.A right axis deviation isusually abnormal. It might indicate pulmonary disease, right ventricularhypertrophy, Q waves from lateral wall myocardial infarction, leftposterior fascicular block, electrolyte derangement, or tricyclicantidepressant overdose, or a ventricular rhythm.
  32. 32. Axis Determination Thompson 33 Extreme Right Axis DeviationNorthWest QuadrantIf the QRS axis is -90 to 180 degrees, something is very wrong (possiblyyour lead placement). This is the right superior quadrant of the hexaxialreference system, but in various publications it can be called an extremeright axis deviation, an indeterminate axis, or a right shoulder axis. It’sbad because it means the heart is depolarizing in the wrong direction.With an extreme right axis deviation, you will have negative QRScomplexes in lead I and negative QRS complexes in lead aVF.- Called ERAD- From -90° to -180°QRS in I & aVF are negative- Check your lead placement!- Probably ventricular: Idioventricular or Paced rhythm
  33. 33. Axis Determination Thompson 34 Cheat SheetThe cheat sheet above is featured in many ECG publications. It is a useful tool if you want to memorize the different QRSmorphologies. This method does not require the use of the hexaxial diagram.
  34. 34. Axis Determination Thompson 35Lets do another:ECG – 2Step 1: Determine the equiphasic lead.Step 2: Find that lead on the diagram.Step 3: Find lead perpendicular to the equiphasic lead.Step 4: Determine if it is positive or negative.Step 5: Find your Axis.
  35. 35. Axis Determination Thompson 36Answer:ECG – 2- The most equiphasic lead is aVR (Don’t let the st-elevation confuse you)- The lead perpendicular to aVR is lead III- Lead III is mostly negative- The hexaxial diagram shows negative lead III at -60 degrees.-60 degrees indicates Left Axis Deviation (LAD)
  36. 36. Axis Determination Thompson 37 The Quadrant MethodOkay, most people aren’t going to memorize the hexaxial diagram, and I doubt they will be carrying the Hexaxial Reference Systemaround with them. Using the diagram is the best way to find the best estimate of the mean electrical axis. However, there is an easierway to determine whether axis deviation exists or not.The quadrant method uses the basics we know about the hexaxial diagram, and allows us to determine axis deviation based oninformation provided by just two leads—Lead I and aVF.- Remember, lead I cuts across the body horizontally, and aVF does the samething vertically.- The positive electrode for lead I is on the left shoulder, at 0 degrees and thenegative electrode is at 180 degrees.- The positive electrode for aVF is at 90 degrees and the negative is at -90.
  37. 37. Axis Determination Thompson 38 The Quadrant MethodRemember the quadrants on the hexaxial reference system? Any QRS axis that falls between 0 and 90 degrees is normal, anythingfrom 90 to 180 is deviated to the right, anything from 0 to negative 90 is deviated to the left, and all axis ranging from negative 90 to180 are in no man’s land, and it is considered extreme right axis deviation.
  38. 38. Axis Determination Thompson 39 The Quadrant Method aVF +Since Lead I has its positive pole on the right side and negative on the left any positive QRS will have an axis to the right of the aVFline, and any negative QRS in Lead 1 will have an axis left of the aVF line.Since aVF has its positive end on the bottom and its negative end up top, a positive QRS in lead aVF will have a QRS axis in one ofthe bottom two circles while a negative QRS in aVF would have an axis in one of the top two quadrants.
  39. 39. Axis Determination Thompson 40 The Quadrant MethodECG – 3
  40. 40. Axis Determination Thompson 41 The Quadrant MethodSee what we did?- Look at Lead I on ECG – 3.- Lead I is mostly positive. Since we know that means the axis is on the right side of our diagram, we shade the left side.- Now look at aVF on ECG – 3- aVF is also positive. Since we know that means the axis is on the bottom, we shade the top.This leaves us with only one quadrant, the SouthEast corner, which we know is the normal quadrant.So we don’t have an exact axis, but we know that it is between 0 & 90 degrees, which is normal.
  41. 41. Axis Determination Thompson 42 The Quadrant Method Cheat Sheet
  42. 42. Axis Determination Thompson 43 Axis DeterminationECG – 4To make things easier, the monitor is usually very good at determining the QRS axis on a clean tracing. This one says 50 degrees.
  43. 43. Axis Determination Thompson 44ECG – 4Lets see how close the two methods are that we learned.Hexaxial Method:Step 1: Determine the equiphasic lead…..aVL is most equiphasicStep 2: Find that lead on the diagram.Step 3: Find lead perpendicular to the equiphasic lead…..Lead IIStep 4: Determine if it is positive or negative……Lead II is positiveStep 5: Find your Axis…….60 degrees—pretty close out of 180 possibilities!
  44. 44. Axis Determination Thompson 45ECG – 4The Quadrant Method tells us that the QRS axis is normal, & a QRS axis of 50 degrees is normal. Both methods work!
  45. 45. Axis Determination Thompson 46 PracticeECG – 5Use the quadrant method to determine if axis deviation exists. Remember, there are four potential conditions:Normal – The axis is between 0 to 90 degreesLeft Axis Deviation (LAD) – The axis is between 0 to -90 degreesRight Axis Deviation (RAD) – The axis is between 90 to 180 degreesExtreme Right Axis Deviation – The axis is between -90 to 180 degrees
  46. 46. Axis Determination Thompson 47 PracticeECG – 5 ECG – 5 is an example of Left Axis Deviation (LAD). - Since Lead I is mostly positive, we shade out the negative (left) side of the diagram. - Since aVF is mostly negative, we shade the positive (top) side of the diagram. - The NorthEast corner is remaining, indicating LAD.
  47. 47. Axis Determination Thompson 48 Part 2 The Precordial Axis
  48. 48. Axis Determination Thompson 49 The Precordial AxisSometimes refered to as “the Z axis”. The remaining six leads of the 12-Lead ECG make up the precordial leads. These leads have anaxis of their own, most often identified by “R-wave progression”. Since determining the exact precordial axis is of little importance,we will only concentrate on whether it’s normal or abnormal. This is much easier than determining the QRS axis in the frontal plane.
  49. 49. Axis Determination Thompson 50 PathologiesOn the right side of the chart above are some common causes of shifts in the precordial axis.Note that an Anterior MI may cause a late transition, or “poor R-wave progression”. This is important, because minimal ST-elevation in V2 to V4 without reciprocal changes, with tall R-waves and a short QTc-interval is almost always early repolarization—acommon STE-Mimic. Conversely, the same findings with poor R-wave progression and a longer QTc are very indicative of anAnterior MI.
  50. 50. Axis Determination Thompson 51 Precordial AxisECG – 6To determine if there is an abnormality of the precordial QRS axis, you only have to observe the precordial leads (also called the“chest leads” or “V leads”). The QRS complexes represent ventricular depolarization (firing of the ventricles to stimulatecontraction). A positive deflection, like an R-wave or an R-prime (secondary R-wave, often seen with Right Bundle Branch Block),occurs when the impulse is traveling towards the lead being observed. A negative deflection, like a Q-wave or S-wave, occurs whenthe impulse is traveling away from the electrode of the lead being observed.
  51. 51. Axis Determination Thompson 52 Precordial Axis This diagram on the right shows a rough representation of where the precordial electrodes are in relation to the heart. The image on the rights shows us the sequence of NORMAL ventricular depolarization.
  52. 52. Axis Determination Thompson 53 Precordial AxisECG – 6Take a look at lead V1 on ECG – 6Since V1 has a very small R-wave (which is normal) as its first deflection, it is safe to say that at the beginning of ventriculardepolarization, the impulse is traveling towards the V1 electrode only momentarily. The QRS complex in V1 then transitions into adeep S-wave, indicating that the impulse travels away from the V1 electrode. This makes since if you consider the image from theprevious page. The intraventricular septum is depolarized first (in the direction of V1), then the impulse travels away from V1.
  53. 53. Axis Determination Thompson 54 Precordial AxisThe R-wave usually begins small, or nonexistent in V1 then becomes larger in V2, V3 and so on until V6, where the QRS complexshould be almost completely positive. The transition from a mostly negative QRS complex to mostly positive QRS complex shouldoccur in either V3 or V4. If the QRS complex stays mostly negative past V4, this is referred to as poor or late R-wave progression,and is indicative of a clockwise rotation of the precordial QRS axis. Conversely, if the R-wave is prominent in V1, and the QRScomplex is more positive than negative, this is called “early R-wave progression”, or counterclockwise rotation of the precordial axis. Normal Transition Zone Early R-Wave Progression Late R-Wave Progression
  54. 54. Axis Determination Thompson 55ECG – 7Take a look at ECG – 7Notice where the QRS complex becomes more positive than negative in the precordial leads? V4 is mostly negative, and then V5seems to be more positive. This is an example of late R-wave progression, or “clockwise rotation” of the precordial axis. ECG – 7 isan example of a Left Bundle Branch Block (LBBB), which is a very common cause of late R-wave progression.* Did you notice that left axis deviation (LAD) is also present on this 12-lead? LBBB may also cause LAD!
  55. 55. Axis Determination Thompson 56ECG – 8Now examine ECG – 8This is an example of early R-wave progression, or a “counterclockwise rotation” of the precordial axis—notice the tall R-waves inV1? QRS complexes in V1 or V2 that are mostly positive are never normal! ECG – 8 happens to be a Right Bundle Branch Block(RBBB), which is a common cause of early R-wave progression. Notice that the QRS complex doesn’t appear very wide at firstglance—it was the precordial axis that helped determine that this was a RBBB.* Another strong indicator of RBBB is terminal S-waves in leads I and V6.** Note: The frontal plane axis is “indeterminate”, because every complex is equiphasic (equally positive & negative).
  56. 56. Axis Determination Thompson 57ECG – 9Here you can see how an anterior MI can alter the precordial axis. By far the most common change is late R-wave progression. Thisclockwise shift in the precordial axis should always be looked for when tying to determine if a 12-lead ECG represents an anteriorinfarct or benign early repolarization (BER). BER will not cause this clockwise rotation of the precordial axis, but an anteriorinfarction will almost always cause a deviation.ECG – 9 also gives us an example of right axis deviation (RAD). There are many common causes of RAD, but a left posteriorfascicular block (LPFB) is the most common. An LPFB can actually result from an infarction.
  57. 57. Axis Determination Thompson 58ECG – 10This is an example of why an anterior infarction would not have poor R-wave progression. The RBBB present on this 12-lead ECGcauses early R-wave progression, and apparently has more effect on the precordial axis than the anterior infarction.* This infarction can be noted by the ST-elevation in V1, and the hyperacute T-waves in V2, V3, & V4.
  58. 58. Axis Determination Thompson 59 Part 3 Practice 12-Lead ECGs
  59. 59. Axis Determination Thompson 60ECG – 1ECG – 2
  60. 60. Axis Determination Thompson 61ECG – 3ECG – 4
  61. 61. Axis Determination Thompson 62ECG – 5ECG – 6
  62. 62. Axis Determination Thompson 63ECG – 7ECG – 8
  63. 63. Axis Determination Thompson 64ECG – 9ECG – 10
  64. 64. Axis Determination Thompson 65ECG – 11ECG – 12
  65. 65. Axis Determination Thompson 66ECG – 13ECG – 14
  66. 66. Axis Determination Thompson 67ECG – 15ECG – 16
  67. 67. Axis Determination Thompson 68ECG – 17ECG – 18
  68. 68. Axis Determination Thompson 69ECG – 19ECG - 20
  69. 69. Axis Determination Thompson 70ECG – 21ECG – 22
  70. 70. Axis Determination Thompson 71ECG – 23ECG – 24
  71. 71. Axis Determination Thompson 72ECG – 25ECG – 26
  72. 72. ECG – 27ECG – 28
  73. 73. Axis Determination Thompson 74ECG – 29ECG – 30
  74. 74. Axis Determination Thompson 75ECG – 31ECG – 32
  75. 75. Axis Determination Thompson 76 Part 4 Answers & Interpretations
  76. 76. Axis Determination Thompson 77ECG – 1ECG – 2
  77. 77. Axis Determination Thompson 78ECG – 1 & ECG – 2These are both examples of Left Ventricular Hypertrophy with a typical Left Ventricular Strain Pattern. Because there is limitedspace on prehospital 12-lead print outs, the monitor actually cuts the depth and height of complexes short. This is to keep extra tall ordeep complexes from interfering with other leads. The ST-Elevation present in the right precordial leads (V1, V2, V3) is entirely dueto the LV-Strain pattern. With LV-Strain, you will typically see ST-Elevation in the right precordial leads, and ST-Depression in theleft precordial leads (V4, V5, V6)."Strain" is a pattern of asymmetric ST segment depression and T wave inversion. LV strain is most commonly seen in one or moreleads that look at the left ventricle (leads I, aVL, V4, V5, V6); less commonly it can be seen in inferior leads.Axis:Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are both positivePrecordial QRS Axis (“V Leads”): Normal transition, The QRS complex transitions frommostly negative to mostly positive in the V3, V4 range. Normal Transition Zone
  78. 78. Axis Determination Thompson 79ECG – 3ECG – 4
  79. 79. Axis Determination Thompson 80ECG – 5ECG – 3, ECG – 4, ECG – 5These are various examples of Left Bundle Branch Block (LBBB). LBBB is most commonly identified by a supraventricular rhythm(p-waves are present), that is wide (greater than 3 small boxes, 120ms), and has a terminal S-wave in V1.Frontal Plane QRS Axis (Limb Leads): Left Axis Deviation, Lead I is positive & aVF is negativePrecordial QRS Axis (“V Leads”): Late R-wave progression, a.k.a. clockwise rotation of the precordial axis. The QRS complextransitions after V4.
  80. 80. Axis Determination Thompson 81ECG – 6ECG – 6Technically this 12-lead tracing represents a “non-specific intraventricular conduction delay”; which is a fancy way of saying that itdoesn’t fit into a right or left bundle branch block category, but there is a slowing of the impulse between the ventricles. However, inthe prehospital environment, it would not be wrong to call this a left bundle branch block—because the terminal wave in V1 isnegative and it is a wide atrial rhythm. This means that STEMI alert should not be called.Frontal Plane QRS Axis (Limb Leads): Right Axis Deviation, Lead I is mostly negative & aVF is positivePrecordial QRS Axis (“V Leads”): Normal R-wave progression
  81. 81. Axis Determination Thompson 82ECG – 7ECG – 8
  82. 82. Axis Determination Thompson 83ECG – 9ECG – 10
  83. 83. Axis Determination Thompson 84ECG – 7, ECG – 8, ECG – 9, & ECG – 10These are all examples of Benign Early Repolarization (BER), “Early Repol”. BER is one of the most common reasons formisdiagnosed STEMI. BER is caused by an elevation of the J-Point due to premature repolarization (recharging) of the ventricles.Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are both positivePrecordial QRS Axis (“V Leads”): Normal R-wave progression, ECG – 8 is slightly later to progress than the others.“Early Repol” Clues - No reciprocal changes – because an MI often causes st-depression in leads opposite to those with elevation - Asymmetrical T-waves – because an early infarction has hyperactute T-waves (tall, broad, & symmetrical) - Concave ST-elevation – because the presence of convex ST-elevation is almost always an MI - Notched J-points – not always present with early repol, but a GREAT indicator that it is NOT an MI - Normal R-wave progression – because a MI often causes poor R-wave progression (clockwise rotation)
  84. 84. Axis Determination Thompson 85ECG – 11ECG – 12
  85. 85. Axis Determination Thompson 86ECG – 13ECG – 11, ECG – 12, & ECG – 13These are all examples of Acute Pericarditis. Note the widespread ST-Elevation amongst the many leads. PR-depression is also acommon finding with pericarditis. The patient’s symptoms may be the biggest clue; positional pain relief is common.Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are both positivePrecordial QRS Axis (“V Leads”): Normal R-wave progression, Acute Pericarditis does not generally affect the electrical axis.
  86. 86. Axis Determination Thompson 87ECG – 14ECG – 14This 12-lead presents as a LBBB vs. Sine-wave. The patient’s history, and presentation should be used come to a solid determination.A Sine-wave is a sign of significant hyperkalemia, and may only last for minutes before degrading into a lethal arrhythmia. A Sine-wave is present when there is a straight line from the tip of the S-wave (nadir) to the peak of the T-wave.Frontal Plane QRS Axis (Limb Leads): Left Axis Deviation, Lead I is positive & aVF is negativePrecordial QRS Axis (“V Leads”): Late R-wave progression
  87. 87. Axis Determination Thompson 88ECG – 15ECG – 15This 12-lead has a great example of peaked T-waves, indicating hyperkalemia. Note the tall, narrow T-waves in nearly every lead.The T-waves are actually larger than most of the QRS-complexes. This is a sign of increased potassium.Frontal Plane QRS Axis (Limb Leads): About 90 degrees, Since Lead I is equiphasic and aVF is perpendicular to Lead I, the QRS axisis inline with aVF, since the QRS complexes in aVF are positive, and the positive end of aVF is at 90 degrees, that is the axis.Precordial QRS Axis (“V Leads”): Normal R-wave progression
  88. 88. Axis Determination Thompson 89ECG – 16ECG – 16This is most likely an early Inferior Wall MI with lateral, and posterior wall extension. If you recall how the coronary anatomy works,the right coronary artery (RCA) is usually the producer of the posterior descending artery (85% of the time). The right coronary arterymay supply the inferior, posterior, and part of the lateral wall of the heart.Frontal Plane QRS Axis (Limb Leads): Normal, about 30 degreesPrecordial QRS Axis (“V Leads”): Normal R-wave progression
  89. 89. Axis Determination Thompson 90ECG – 17ECG – 17This is an example of an Antero-Septal MI, with some lateral wall extension. This is likely due to a proximal occlusion of the LeftAnterior Descending coronary artery (LAD). The LAD, termed “Widow Maker”, supplies predominately the left ventricle.Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are both positivePrecordial QRS Axis (“V Leads”): Late R-wave progression, V4 is equiphasic—it should be mostly positive.
  90. 90. Axis Determination Thompson 91ECG – 18ECG – 18This is an example of an extensive Inferior Wall MI (IWMI), with posterior & lateral wall extension. Just like ECG-16, this isprobably due to a proximal RCA occlusion. Since the angle of lead III’s view obtains a better picture of the right ventricle than theangle of lead II, if lead III has more ST-elevation than lead II it is an indicator of right ventricular infarction.Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are both positive.Precordial QRS Axis (“V Leads”): Normal R-wave progression, note that V1 & V2 have developed R-waves (indication of PWMI).
  91. 91. Axis Determination Thompson 92ECG – 19ECG – 19This is another example of an Antero-Septal MI. Often, multiple sides of the heart are affected simultaneously. The anterior wall, andseptum are commonly infarcted together. Our knowledge of the precordial axis tells us that leads V3 & V4 were probably reversedon this patient. This means that V3 on this tracing is actually in the V4 position and visa versa.Frontal Plane QRS Axis (Limb Leads): Normal, about 0 degrees.Precordial QRS Axis (“V Leads”): Normal R-wave progression, V3 & V4 misplaced.
  92. 92. Axis Determination Thompson 93ECG - 20ECG – 20This is a rare example of an isolated Lateral Wall Infarct. This injury pattern is nearly always due to an occlusion to the LeftCircumflex (LCx). 5 Easy Steps Step 1: Determine the equiphasic lead. Step 2: Find that lead on the diagram.Frontal Plane QRS Axis (Limb Leads): Normal, about 60 degrees. Step 3: Find the perpendicular lead.Precordial QRS Axis (“V Leads”): Normal R-wave progression Step 4: Determine if it is positive or negative. Step 5: Find your Axis.
  93. 93. Axis Determination Thompson 94ECG – 21ECG – 21This is an example of an Inferior Wall MI, with probable posterior wall extension. Its important to note that since aVR is the mostreciprocal lead to Lead III, it almost always has some form of reciprocal change present with an IWMI. The most common change isdownwardly sloping ST-depression.Frontal Plane QRS Axis (Limb Leads): Normal, about 90 degrees. Since lead I is equiphasic, the axis is inline with aVF.Precordial QRS Axis (“V Leads”): Normal R-wave progression
  94. 94. Axis Determination Thompson 95By using what we have learned about axis, we can more easily understandwhat we are looking at on the 12-Lead ECG. The image to the right has afew of the leads placed with arrows pointing away from where the positiveelectrodes would be placed. This easily explains why leads II, III, & aVFare the “inferior leads”. It also illustrates why aVL and lead I are the aVL“high lateral leads”. Also, note how aVL and lead III are nearly oppositeeach other. This is the reason that nearly every inferior MI has a Lead Ireciprocal change found in aVL. Finally, note the angle of lead III, it has anear perfect picture of the right ventricle; which is why ST-elevation inlead III which is greater than ST-elevation in lead II indicates a right-sidedinfarction. Lead III aVF Lead II
  95. 95. Axis Determination Thompson 96ECG – 22ECG – 22This is an example of Wellen’s Phenomenon. Sometimes called Wellen’s warning, syndrome, or sign, this phenomenon is anindication of an impending anterior infarction. This phenomenon does NOT always occur. Wellen’s may also present as a biphasicT-wave, usually found in V2.Frontal Plane QRS Axis (Limb Leads): NormalPrecordial QRS Axis (“V Leads”): Normal R-wave progression
  96. 96. Axis Determination Thompson 97ECG – 23ECG – 23This is another Antero-Septal Infarct with lateral wall extension (seen best in aVL). Remember that leads aVL & III are the mostreciprocal to each other. If you see ST-segment changes in one of these leads, immediately look for inverse changes in the other. Asyou can see on this ECG, there is STE in aVL, and ST-depression in lead III.Frontal Plane QRS Axis (Limb Leads): Normal, lead III is mostly negative, meaning that the axis is probably between 0º & -30ºPrecordial QRS Axis (“V Leads”): Late R-wave progressionNote: a QS-wave in V2 is always a sign of infarction (new or old). This rule is completely reliant on proper lead placement.
  97. 97. Axis Determination Thompson 98ECG – 24ECG – 24This is an Inferior Wall MI with Posterior Wall extension. Notice the hyperacute T-waves in the inferior leads (II, III, & aVF), andthe reciprocal changes in the high lateral leads (I & aVL)? The amount of ST-elevation is significant due to the QRS-complex havingsuch low voltage.Frontal Plane QRS Axis (Limb Leads): NormalPrecordial QRS Axis (“V Leads”): Late R-wave progression
  98. 98. Axis Determination Thompson 99ECG – 25ECG – 25This is another example of an Inferior Wall MI with posterior changes, most likely due to a proximal occlusion of the right coronaryartery (RCA). The RCA is connected to the posterior descending artery in 85% of the population; the left circumflex (LCx) suppliesthe PDA in the rest of people.Frontal Plane QRS Axis (Limb Leads): NormalPrecordial QRS Axis (“V Leads”): Normal R-wave progression, its difficult to tell how tall the QRS complexes in V4 are because theyare cut off by the monitor.
  99. 99. Axis Determination Thompson 100ECG – 26ECG – 26This ECG is an example of Right Bundle Branch Block (RBBB). RBBB is presentwhen a wide supraventricular rhythm presents with a positive terminal deflection in V1.Other findings include appropriate T-wave discordance, and a slurred S-wave in Lead Iand V6.Frontal Plane QRS Axis (Limb Leads): Indeterminate, all frontal leads are equiphasic.Precordial QRS Axis (“V Leads”): Early R-wave Progression
  100. 100. Axis Determination Thompson 101Right Bundle Branch Block Explained The right bundle branch consists of one fascicle. When this fascicle is blocked, the conduction that normally travels from the atria is routed away from the right bundle branch and towards the healthy left bundle branch (1). The conduction travels fast to the V1 health left bundle branch (2). After the left ventricle is fully depolarized, the conduction moves slower to depolarize the right 1 + ventricle through cell-to-cell conduction (3). 2 I & V6 This is why with a RBBB you will see a terminal R-wave in V1 3 and terminal S-wave in V6, because the last flow of conduction moves towards V1 and away from V6.A Right Bundle Branch block may cause Right Axis Deviation in the frontal plane, because of the S-waves that occur in lead I as aresult of the above-mentioned conduction abnormality. It may also cause early r-wave progression in the precordial axis due to thelarger-than-normal R-wave in V1.
  101. 101. ECG – 27ECG – 27This is an early Antero-Septal MI. This 12-lead doesn’t meet STEMI Alert criteria, but the ST-morphology in V1, hyperacute T-waves in V2 & V3, and the reciprocal changes in the inferior leads are highly suggestive of MI.Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are mostly positivePrecordial QRS Axis (“V Leads”): Normal R-wave Progression
  102. 102. Axis Determination Thompson 103ECG – 28ECG – 28This is an example of Atrial Bigeminy with an Anterior Infarct. 5 Easy StepsFrontal Plane QRS Axis (Limb Leads): Left Axis Deviation, about -30º Step 1: Determine the equiphasic lead.Precordial QRS Axis (“V Leads”): Normal R-wave Progression Step 2: Find that lead on the diagram.Lead II is the most equiphasic, and aVL is perpendicular to lead II. aVL is Step 3: Find the perpendicular lead.positive on the strip above, and the positive end of aVL is at -30 degrees on Step 4: Determine if it is positive or negative.the hexaxial reference system. Step 5: Find your Axis.
  103. 103. Axis Determination Thompson 104ECG – 29ECG – 29This ECG is that of a Right Bundle Branch Block (RBBB) with Antero-Septal Infarction.Frontal Plane QRS Axis (Limb Leads): Left Axis Deviation, about -30ºPrecordial QRS Axis (“V Leads”): Early R-wave Progression, counter-clockwise rotation of precordial axisEarly R-wave progression is commonly caused by a right bundle branch block. The left axis deviation on this 12-lead is on the edgeof being considered pathological, and a Left Anterior Fascicular Block (LAFB) is probable. A RBBB in conjunction with a LAFB isconsidered a bifascicular block, and alerts us that only a single fascicle is still conducting impulses; the laft posterior fascicle.
  104. 104. Axis Determination Thompson 105ECG – 30ECG – 30This is an example of Global Ischemia.Frontal Plane QRS Axis (Limb Leads): Physiologic Left Axis Deviation, about 0ºPrecordial QRS Axis (“V Leads”): Normal R-wave Progression, it is easier to determine that the QRS complexes in V4 are mostlypositive if you examine the last few complexes.Remember that lead I is at 0 degrees. This would explain why this tracing has nice tall QRS complexes in lead I.
  105. 105. Axis Determination Thompson 106ECG – 31ECG – 31This is an Anterior Wall Infarct. The STEMI is not obvious, but present in V3 through V6.Frontal Plane QRS Axis (Limb Leads): NormalPrecordial QRS Axis (“V Leads”): Late R-wave Progression, a common finding with an Anterior Wall MI.
  106. 106. Axis Determination Thompson 107ECG – 32ECG – 32This is an example of Reversed Limb Leads.When lead I is negative and aVR is positive, there should be a concern about limb leadreversal. aVR will almost never be this positively deflected with a supraventricularrhythm. One of the concerns with not identifying this problem is the misinterpretation ofthe 12-lead. This 12-lead looks to have ST-elevation when it is entirely due to themislplaced limb leads.