Atrial Tachycardia Mechanisms and Localization

Atrial Tachycardia
蔡佳醍醫師
台大醫院心臟內科
1

Atrial Tachycardia
 Atrial tachycardias (ATs) are an uncommon cause of
supraventricular tachycardia (SVT):
 Adults - 5% of all SVTs subject to EP studies
 Pediatric patients:
 10-15% of the SVTs in pediatric patients without
congenital heart defects (CHD)
 More in those who have undergone a surgical correction
of their CHD

(Zipes DP, Jalife J. Cardiac Electrophysiology: From cell to bedside, 4th edition. 2004; pg. 500)

2

Atrial Tachycardias
 Locations:
Tachycardia originating in
atrial muscle at a site(s) other
than the sinus node or the AV
node.
 Mechanisms:
Abnormal automaticity,
trigger activities, or reentry

3

Mechanisms based on Ablation
 Focal AT: activation spreading from a single
focus either radially, circularly or centrifugally
without an electrical activation spanning the
tachycardia cycle length.

4
(Zipes DP, Jalife J. Cardiac Electrophysiology: From cell to bedside, 4th edition. 2004; pg. 500-501)

Classification of Mechanisms
 Macroreentrant : reentry occurring over fairly large
well-defined circuits that span the entire tachycardia
cycle length(>70%). Also the earliest and latest atrial
activations are in close proximity.

The various patterns are:
 Single loop (like typical atrial flutter)
 Figure of eight (made up of two loops)
 Reentry through narrow channels adjacent to scar,
anatomic barriers (i.e. tricuspid annulus)

5

Focal Atrial Tachycardias

6

• Focal atrial tachycardia has three mechanisms:
automaticity, triggered activity and microreentry.
• Automatic atrial tachycardia is identified by the presence
of the following characteristics:
• AT can be initiated by an isoproterenol infusion
• PES cannot initiate or terminate the AT
• AT can be gradually suppressed with overdrive pacing, but
then resumes with a gradual increase in the atrial rate
• AT is terminated by propranolol
• AT episodes have a “warm up” and/or “cool down
phenomenon
• AT cannot be terminated by adenosine

7

Triggered activity is identified by the presence of the following
characteristics:
• AT can be initiated with rapid atrial pacing
•No entrainment is observed, but overdrive suppression or
termination occurs
• Delayed afterdepolarizations can be recorded near the origin
using a monophasic action potential catheter before the AT
onset, but not at sites remote from the tachycardia
• AT terminated by adenosine, propranolol, verapamil,
, Valsava maneuvers and carotid sinus pressure

8

Microreentry is identified by the presence of the
following characteristics:
• AT can be reproducibly initiated and terminated by
atrial pacing and extrastimuli
• No delayed afterdepolarizations can be recorded using
a monophasic action potential catheter
• Manifest and concealed entrainment observed while
pacing during the tachycardia

9

Focal Atrial Tachycardia

∗ ∗

Focal AT in a post-open heart patient with the focus originating in the
right atrial free wall with centrifugal spread of the activation.
10

MOST COMMON SITES
 Right Atrium
– Right Atrial Appendage
– Coronary Sinus Ostium
– Crista Terminalis

 Left Atrium
– Pulmonary Vein Ostia
– Left Atrial Appendage

11

Focal Atrial Tachycardia - Right
Atrial Appendage
Right Atrial
Appendage

13 AP View

Focal Atrial Tachycardia – Coronary
Sinus Ostium

LAO VIEW

Tricuspid Valve

Effective Site

14 CS Os LAO View

Focal Atrial Tachycardia – Left Sided
Focus (RA Septum is Early)
PA VIEW OF
RA

SEPTUM

HIS

CS OS

15 PA View

Electrocardiographic Localization of Focal AT

• Focal atrial tachycardia is characterized by P waves separated by an isoelectric interval in
all ECG leads.
• The P-wave can often be obscured by the T wave or QRS complexes during the
16tachycardia.

Focal AT Sites

17
(Tada H, et al. Simple Electrocardiographic Critera for Identifying the Site of Origin of Focal Right Atrial Tachycardia. PACE 1998;21[Pt. II]:2431-2439

Electrocardiographic Localization of Right Focal AT

Short-PR

18

AT Arising from the Crista Terminalis

• The CT is a common site for ATs (as much as 75% of right ATs).
• CT demonstrates marked anisotropy due to poor transverse cell
to cell coupling. This may create slow conduction and thus
microreentry. Also the CT contains a cluster of cells with
automaticity.
• If superolateral, they will have positive P-waves in leads, II, III
and aVF. If inferolateral, they will have negative P-waves in
leads, II, III and aVF.

19

Representative Focal AT 12-Lead ECGs

A: A CT-AT that originated from segment 1. B: A CT-AT that originated from segment 2.
20

AT Arising from the AV Annulus

• ATs arising for the tricuspid annulus are relatively uncommon,
accounting for only about 13% of right atrial ATs. The P-wave
will be negative in the precordial and inferior leads.
• ATs may also arise form the mitral valve annulus. In that case the
P-waves are negative in aVL and positive in V1.
• The demonstration of cells with AV nodal EP properties
lacking connexin43 near the annulus, the mechanism is believed
to be microreentry involving these nodal-like cells.

21

Representative Focal AT 12-Lead ECGs

A: A TA-AT that originated from segment 1. B: A TA-AT that originated from segment 3. C:
A Sep-AT that originated from near the apex of Koch’s triangle, showing narrow P waves
with an initial large negative and a late small positive component in leads II, III and aVF.
22

AT Arising from the CSos Musculature

• Focal ATs of up to 12% of right ATs occur in the area around the
CSos, outside or just inside the os.
• In very rare cases, AT can occur from deep in the CS and arises
from the CS musculature. These cannot usually be ablated from
the left atrial endocardium and need to be ablated from within the
CS.
• A negative P-wave in V6 is often seen in ATs originating from
the CSos.

23

AT Arising from the Atrial Septum

•These ATs are sensitive to lower doses of adenosine than ATs arising
from the crista terminalis. These also more often require the use of
isoproterenol to induce than right atrial free wall ATs.
•In up to 10% of ATs in the right atrium can arise from the apex of
Koch’s triangle (para-hisian). These are adenosine sensitive and can
be induced with isoproterenol. These can usually be ablated without
damage to the AV node.
•The P-wave duration for these ATs is on average 20 msec shorter
during AT than sinus rhythm.
•In these patients it is important to map both the right and left atria. In
patients with a left-sided origin, the P-waves can be either positive or
negative in V1, so it is misleading. Up to 40% of patients with the
earliest activation recorded in Koch’s triangle have a left atrial focus.

24

Sinus Node Reentrant Tachycardia
•Sinus Node Reentrant Tachycardias are presumed to be
due to microreentry in the tissue near the sinus node or the
perinodal region (superior crista terminalis). The P-Wave
morphology is identical to that during sinus rhythm.

•Focal ATs may also arise from the superior vena cava
(SVC). Those ATs arising from around the SVC may
conduct to the right atrium (RA).

25

Inappropriate Sinus Tachycardia
• The hallmark feature of inappropriate sinus tachycardia (IST) is
a consistently elevated resting heart rate and exaggerated heart
rate response to low levels of physical activity.

•Some patients may have primary autonomic abnormalities,
including postural orthostatic tachycardia syndrome. Others may
have primary abnormalities of the sinus node.

• These patients show a blunted response to adenosine (0.1 to 0.15
mg/kg) with less of a sinus cycle length prolongation than age-
matched controls. Thus structural abnormalities of the sinus
node are the cause of IST in those patients.

26

ECG Differential Diagnosis of AT

• ATs, especially septal ATs, need to be differentiated from
concealed septal bypass tracts, AV node reentry (fast-slow atypical
AVNRT).
1. When AV block occurs, a bypass tract can be ruled out (AV block
also observed in AV node reentry).
2. Adenosine may also terminate AT.
3. Only AT patients experienced oscillations in the atrial cycle
length.

27

ECG Differential Diagnosis of AT
• Burst pacing from the right ventricle for 3-6 beats during
the tachycardia at a cycle length faster than the
tachycardia results in:1) tachycardia termination; 2)
entrainment of the tachycardia; 3) dissociation of the
ventricle from the tachycardia.

• If the ventricles are dissociated from the tachycardia, a
bypass tract is excluded.

• If burst RV pacing reproducibly terminates the
tachycardia, without conduction to the atrium, AT is
excluded.
28

RV overdrive pacing to DD septal AT from septal
AP or atypical AVNRT

• Ventricular burst pacing can also be performed for longer
periods of time at a rate just slightly faster than the tachycardia
cycle length.

• If the atrial activation sequence during pacing is different than
that during tachycardia, an AT is present.

• When pacing is stopped, and the ECG sequence following the
last paced ventricular beat demonstrates a V-A-A-V response,
an AT is present.

29

AT with a VAAV Pattern

Immediately after the last paced ventricular beat (S), atrial tachycardia
with a variable degree of atrioventricular (AV) block is demonstrated,
with a typical VAAV pattern.
30

RA overdrive pacing to DD septal AT from septal
AP or atypical AVNRT
• Overdrive right atrial pacing during the tachycardia at a
cycle length slightly faster than the tachycardia cycle
length can cause termination or tachycardia continuation
upon cessation of pacing.

• VA interval measured from the onset of the surface QRS
on the first postpacing ventricular beat to the onset of the
atrial electrogram on the His catheter of the return cycle.

• If the VA interval is within 10 msec of the VA interval
during the tachycardia, the tachycardia is due to AVNRT
or a bypass tract. If the AV interval is variable or
different, AT is present.
31

DD septal AP from atypical AVNRT

32

Mechanisms of Macroreentrant AT

33

Macroreentrant Atrial Tachycardia

LIPV

Macroreentrant AT originating near the LIPV and propagating
34
around the Mitral valve.

Specific Types of Macroreentrant AT
• Sites of macroreentrant ATs:
• Right atrium
• Left atrium
• Biatrial
• Left atrial septum
• Right pulmonary veins (single loop and figure of eight)
• Between 2 areas of low voltage or around one such area
• Left atrial flutters
• Reentry involving the CS and its musculature

35

Entrainment: Fusion
This is a demonstration of pacing with fusion.

36

Entrainment: Progressive Fusion

37 14. Waldo A. JCE. 1997;8:341.

Concealed Entrainment
This is a demonstration of concealed entrainment.

38

PPI :Post pacing interval FCL: Flutter cycle length

15. Lesh et al. JCE Vol.7,No 4, April 1996
39

Post Pacing Interval (PPI) in
Entrainment with Fusion
Return cycle length= (Time from pacing site)x2 +TCL

The reentry circuit = Tachycardia cycle length (TCL)

PLUS

Time from pacing site to the circuit

PLUS

Time from circuit to the pacing site

=Return Cycle Length

= pacing site
40

PPI in Concealed Entrainment
If the pacing occurred inside of the tachycardia circuit, the time
it takes for the tachycardia to resume will be the tachycardia
cycle length only, since there is no distance out side of the
circuit to add time.

Return cycle length= (Time from pacing site)x2 +TCL

= pacing site

41

Entrainment Mapping

8. Olgin, et. al., Journal of Cardiovascular Electrophysiology,
42 Vol.7, No.11, Nov 96.

Double Potentials
 Double potentials are indicative of a line
of block
 Lines of block are either fixed or
functional
– Atriotomy sites and the eustachian ridge
are examples of fixed lines of block
– Evidence exists that block in region of
crista terminalis during atrial flutter is a
form of functional conduction block
43

Double Potentials (con’t)

44

Double Potentials at CT during AFL

45

Ablation of Atrial Tachycardia

 Key Locations
– Identification of Focal Sites (if applicable) -
Focal
– Identification of Anatomical Barriers (if
applicable) - Macroreentrant
– Identification of Scar (if applicable) –
Microreentrant (Focal)
46

Mapping and Ablation Techniques: Focal AT
Once a focal mechanism has been determined, the site is
targeted by detailed atrial endocardial mapping during
the AT or ectopic beats. A knowledge of the most
common sites and the P-wave morphology can facilitate
the mapping and ablation.
•Leads aVL and V1 are helpful to distinguish right from
left atrial foci (isoelectric or - aVL/+V1 = left; + or
biphasic aVL/- or biphasic V1 = right).
•Positive P waves in the inferior leads suggests a superior
or anteripr focus, and biphasic or negative indicates
posterior or inferior.
•A negative P-wave in aVR = a right atrial focus.
47


Endocardial Activation Mapping:
• Use HRA, His, CS catheters to regionalize the AT origin
based on the activation pattern.
• Next the ablation catheter is inserted and moved to find
the site of earliest activation relative to the onset of the
surface P-wave or onset of activation at the CSos or HRA
which is in a known fixed relationship to the P-wave onset
during AT.

48

Endocardial Activation Mapping:

• Fractionated or prepotentials (spikes) are also successful
ablation sites, but the specificity and sensitivity is low.
• Intermittent mechanical block of the AT with catheter
manipulation is also a good indicator of a successful site,
but care must be taken to avoid loss of conduction for
hours.

49

Focal Ablation
Focal Ablation:

•Acceleration of the tachycardia before termination is an
excellent sign.
•Also rapid termination of the tachycardia within 10
seconds of starting the RF delivery is also a good sign.
•Successful focal ablation is verified by failure to
reinduce the AT before and during an isoproterenol
infusion.

50

Focal Ablation (Cont.)
Focal Ablation:
•Ablation at the atrial septum or Koch’s triangle can cause
AV block. However, the presence of a His potential is not
a contraindication for ablation. The energy needs to be
titrated in such cases, by starting with 10 Watts and
increase with 5-10 Watt increments to a maximum of 40
Watts with continuous AV conduction monitoring to
prevent AV block.
• If the earliest site is the para-hisian area, right PV ectopy
or LA origin need to be ruled out.
• If the earliest site is the superior crista, right PV ectopy
also need to be ruled out. Another unusual potential site
is the SVC.

51

Atrial Tachycardia
CARTO Sucks

Crista Terminalis
SVC

TV

IVC

52 RAO View

Left Atrial Tachycardia

53

Left Atrial Tachycardia

54

Focal Atrial Tachycardias Ablation Sites

This shows the ablation sites in a large group of AT ablation cases.

55

Mapping and Ablation Techniques:
Macroreentrant AT (I)
Conventional methods include activation and entrainment mapping to
identify the obstacles and boundaries of the reentrant circuits, and the
critical isthmus within the reentrant circuit that becomes the target of
the ablation.
• The entire circuit can be mapped with the earliest and latest
activations being adjacent (head meets tail).
• Striking changes in signal amplitude, timing or both with very
slight shifts in the catheter position indicate anatomic barriers to
conduction.
• A combination of diastolic potentials and concealed entrainment
pacing with the post-pacing interval within 20 msec of the TCL
identifies a “protected isthmus” within the reentrant circuit.

56

Mapping and Ablation Techniques:
Macroreentrant AT (II)
• Macroreentrant AT can arise from upper loop reentry in the right
atrium due to a conduction gap in the crista terminalis (CT). Lower
turn-around points are located at the conduction gaps in the CT. RF
linear ablation of the conduction gap (narrowest part of the
reentrant circuit) effectively abolishes the right free wall AT.
• Left atrial reentrant substrates are mostly at the posterior wall, the
PV ostium or base of the appendage. Left atrial marcroreentrant AT
is highly variable of 1-3 loops rotating around the mitral annulus,
PVs and zone of block or a silent area.
• 3D mapping is usually needed in LA macroreentrant AT.

57

Atrial Tachycardia Mechanisms and Localization

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