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Common AVNRT
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The Electrophysiology Laboratory and Electrophysiologic Procedures
dependent on the prevalence of structural heart disease in the population being studied. In patients with structurally normal hearts and no
suggestion of ischemia, EPS has a low yield and an increased likelihood of false-positive results. In patients with a history of coronary
artery disease and segmental wall motion abnormality or conduction
disease on ECG, EPS has a relatively high yield and may rule out
potentially life-threatening causes of syncope, such as sustained ventricular arrhythmia. In an unwitnessed syncope episode, the cause of
the patient’s syncope is never certain, and there is always the potential
for inaccurately attributing the patient’s syncope to an abnormality
detected on EPS. It is desirable that a patient’s symptoms be reproduced by induced arrhythmia.
Supraventricular Tachycardia
The treatment of SVT has undergone dramatic change because radiofrequency catheter ablation offers a high probability of cure with a low
complication rate for many reentrant tachycardias. Although the relationship between the QRS complex and P waves on the 12-lead ECG
may suggest the mechanism of SVT, performance of a detailed EPS is
the only method of accurately characterizing the mechanism of tachycardia and defining the anatomic substrate.
The most often obser ved mechanism of narrow-complex SVT is
atrioventricular nodal reentrant tachycardia (AVNRT), which usually
involves slow- and fast-conducting pathways within or near the AV
node. Although it was previously thought that AV nodal reentry
occurred entirely within the compact AV node, experience from radiofrequency catheter ablation indicates that extranodal tissue may be
involved in the reentrant circuit. Dual AV nodal pathways are characterized by discontinuous AV nodal conduction curves (see Fig. 6-24,
B). In typical AV nodal tachycardia, which constitutes more than 90%
of AVNRT, antegrade conduction occurs over the slow pathway and
retrograde conduction occurs up the fast pathway (slow-fast tachycardia) (Fig. 6-28). Retrograde ventriculoatrial conduction time is usually
short, and atrial depolarization often occurs simultaneously with or
immediately after ventricular depolarization. On surface ECG, the P
waves are either not visible or occur in the ST segment with a short
R–P interval.
(antegrade slow–retrograde fast)
A
Slow
pathway
H
Figure 6-28 Schematic representation of the common form of atrioven-
tricular nodal reentrant tachycardia (AVNRT). In the typical form of AV nodal
tachycardia, antegrade block occurs in the fast pathway, forcing antegrade
conduction down the slow pathway. If antegrade conduction down the slow
pathway is slow enough to allow retrograde conduction to occur up the previously refractor y fast pathway, reentrant tachycardia ensues. Although previously it was thought that the limbs of the tachycardic circuit were contained
within the compact AV node, more recent studies using radiofrequency ablation for AV nodal tachycardia suggest that perinodal tissue is contained in
the reentrant circuit.
Fast
pathway
No visible P waves
Short P–R interval
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The Electrophysiology Laboratory and Electrophysiologic Procedures 313
Another common mechanism of SVT is AV reciprocating tachycardia, using an extranodal AV bypass tract (also referred to as an
accessory pathway). The most common type of accessory pathway is
the bundle of Kent, which occurs in WPW syndrome. The accessory
pathway may be between the RA and ventricle or LA and ventricle. In
an individual patient, an accessory pathway may be capable of antegrade conduction, retrograde conduction, or both. Individuals with
antegrade conduction over an accessory pathway exhibit a short P–R
interval and a wide QRS complex because of ventricular preexcitation (this is also referred to as a delta wave). The axis of the delta
wave and morphology of the QRS depend on the position of the accessory pathway and the amount of tissue depolarized through accessor y
pathway conduction compared with conduction over the normal AV
node. During sinus rhythm, activation of the ventricle can occur over
the accessory pathway and through the normal conduction pathway
using the AV node (see Fig. 6-31, A). QRS morphology results from
fusion of the two mechanisms of ventricular activation. Pathways
capable of only retrograde conduction are referred to as concealed
pathways, and no ventricular preexcitation (or delta wave) is present
on the ECG.
WPW syndrome is characterized by the presence of ventricular
preexcitation (short P–R interval and delta wave on ECG) and the
clinical occurrence of arrhythmias. In patients with WPW syndrome,
the most common type of SVT is orthodromic tachycardia, in which
antegrade block occurs in the accessory pathway and a reentrant
circuit is established with antegrade conduction occurring over the AV
node and retrograde conduction up the accessory pathway (Fig. 6-29,
A-B). In orthodromic tachycardia, the QRS is narrow unless aberrancy
occurs and there is a short R–P interval on the surface ECG. A less
common type of tachycardia in patients with WPW syndrome is antidromic tachycardia, which is a reentrant tachycardia with antegrade
conduction occurring over the accessory pathway and retrograde conduction through the AV node (Fig. 6-29, C ). Antidromic tachycardia is
a regular wide-complex tachycardia that may resemble VT on surface
ECG. Compared with the general population, patients with WPW syndrome have an increased incidence of AF, and conduction to the
ventricle may occur over the accessory pathway and the AV node (Fig.
6-29, D). The QRS morphology depends on the relative amount of
conduction occurring through the accessory pathway compared with
the normal conduction system. In patients with pathways capable of
antegrade conduction and AF, rapid ventricular responses may occur
with a potential for degeneration to VF. During EPS in patients with
WPW syndrome, it is important to induce AF and observe the shortest
R–R interval that shows ventricular preexcitation to assess the antegrade ERP of the accessory pathway and the risk of sudden cardiac
death. Patients who have WPW syndrome and are resuscitated from
VF usually have inducible AF with a rapid ventricular response and
shortest preexcited R–R interval of <
stimulation with single premature extrastimuli defines the antegrade
ERP of the accessory pathway. Programmed stimulation of the ventricle shows the retrograde conduction properties of the accessory
pathway and defines retrograde ERP.
250 msec. Programmed atrial
Catheter Ablation
Catheter ablation is an interventional discipline within EP whereby an
arrhythmogenic focus or critical portion of an arrhythmia circuit is
identified, localized, and subsequently destroyed by means of a percutaneous transcatheter technique. Arrhythmias that are currently
amenable to ablative therapy include AF, atrial flutter, ectopic atrial
tachycardias, SVTs caused by AV nodal reentry or accessory bypass
tracts, and VT. Many modalities have been used for ablation.
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SA
The Electrophysiology Laboratory and Electrophysiologic Procedures
Sinus rhythm
AV
AP
A
B
C
AP
AP
Fusion of antegrade conduction
over AP and AV node
Orthodromic tachycardia
APC
AV
Antegrade – AV node
Retrograde – AP
Narrow QRS complex
Antidromic tachycardia
APC
Antegrade – AP
Retrograde – AV node
Wide QRS complex
Atrial fibrillation
AV
AP
D
Figure 6-29
Schematic representation of possible rhythms in a patient with an acces sory atrioventricular (AV) bypass tract. A, During sinus rhythm, the ventricle
may be activated by conduction over the accessory pathway (AP) and through
the normal AV conduction system. The QRS complex may be narrow if the
ventricle is activated primarily by conduction through the AV node. The QRS
complex is wide and preexcited if activation of the ventricle occurs primarily
via the AP. B, During orthodromic reentrant tachycardia, antegrade conduc tion occurs through the AV node and normal conduction system, whereas
retrograde conduction occurs via the AP. The resulting tachycardia has a
narrow QRS morphology. C, Antidromic tachycardia uses the AP as the
antegrade limb of the reentrant circuit and the AV node and normal conduction system as the retrograde limb. The resulting tachycardia has a wide
QRS complex. D, When atrial fibrillation (AF) occurs in a patient with manifest
accessory pathway, antegrade conduction to the ventricle may occur through
the AV node or over the AP. Morpholog y of the QRS complex may be narrow
and occurs primarily through the AV node, or wide and preexcited if conduction occurs over the accessory pathway. The morpholog y of the QRS complex
may vary beat by beat during AF. SA, Sinoatrial.
Possible rhythms in Wolff-Parkinson-White (WPW) syndrome.
Fusion of antegrade conduction
over AP and AV node
Varying QRS morphology
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The Electrophysiology Laboratory and Electrophysiologic Procedures 315
Historically, direct current energy was the initial energy source used
for ablative procedures, dating back to the early 1980s.
More recently, radiofrequency energy has become the energy
source most commonly used for ablative therapy. Radiofrequency
energy uses a frequency range from 200 to 1200 kHz. Application of
radiofrequency current causes tissue desiccation in a well-localized
region at the point of catheter contact, resulting in a small discrete
lesion approximately 0.5 ×
quency energy–induced lesions has made it the energy source of
choice for most ablative procedures. Available technology allows for
regulation of temperature at the electrode-tissue interface, ensuring
adequate contact and preventing sudden impedance rises. Other
energy sources for ablation, such as microwave and ultrasound, are
being investigated.
0.5 cm2. The localized nature of radiofre-
Indications for Ablation Therapy
Atrial Fibrillation
Catheter destruction of the AV junction has been used to treat patients
with AF and rapid ventricular responses refractory to medical therapy.
Patients who are intolerant of medical therapy and patients not desiring lifelong medical therapy are also candidates for this procedure,
wherein CHB is created and a permanent ventricular pacemaker is
required to normalize HR. Key points to remember when considering
this procedure are the following:
1. Following the procedure, the patient is completely pacemaker
dependent.
2. The procedure does not obviate the need for anticoagulation.
3. There is a risk of developing polymorphic ventricular arrhythmias
early after the procedure, and the ventricular pacing rate should be
90 bpm for the first 2 to 3 months after ablation.
During the past decade and a half, ablation procedures have been
developed in an attempt to eliminate AF. Initial attempts were to create
linear lesions in the left and right atria, similar to the surgical (Maze)
procedure. More recently, observations that pulmonary veins can be
sites for electrical discharges that can initiate AF have created a revolution in interventional EP. In patients with paroxysmal AF, three important randomized clinical trials have shown that catheter ablation is
superior to antiarrhythmic drug therapy (Pappone et al, Jais/Wilber
et al, Wilbur et al). In these trials, freedom from AF was achieved in
63% to 93% of patients who underwent ablation, compared with 17%
to 35% who were assigned to drug therapy. More than one ablation
may be required to achieve success rates in the higher range. Predictors of success include absence of persistent AF, presence of smaller
atria, age younger than 70 years, absence of significant atrial enlargement, and fibrosis. Ablation can be considered for patients with “symptomatic” AF despite antiarrhythmic drug therapy or intolerance to
medications.
Atrial Flutter
In patients who present with atrial flutter, controlling the ventricular
response and maintaining sinus rhythm with medications are more
difficult than is the case in AF. Often, patients need polypharmacy,
and many experience side effects of the medications. Generally, physicians are more likely to recommend ablation early on for patients who
present with atrial flutter, especially if the reentrant circuit is felt to be
in the RA.
Ectopic Atrial Tachycardias
Ectopic atrial tachycardia, also known as automatic atrial tachycardia,
may be mapped and ablated. This procedure is now a front-line
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therapy for medically-resistant ectopic atrial tachycardias as a more
economical and less invasive alternative to traditional surgical isolation procedures.
The Electrophysiology Laboratory and Electrophysiologic Procedures
Atrioventricular Nodal Reentry Tachycardia and
Wolff-Parkinson-White Syndrome
The usefulness of catheter ablation is described best in the category
of reentrant tachycardias that includes the more common mechanisms of SVTs: AVNRT and tachycardias associated with accessory
bypass tracts. The indication for catheter ablation in this group of
arrhythmias includes recurrent symptomatic tachycardias. Ablation
therapy has become a front-line therapeutic option for patients with
paroxysmal SVT, obviating the need for therapy with antiarrhythmic
agents. Another important indication for radiofrequency ablation is AF
in the setting of an accessor y pathway capable of conducting in an
antegrade manner. These pathways have the potential for extremely
rapid conduction, resulting in dangerously rapid ventricular responses
with rates exceeding 250 bpm. In this clinical setting, degeneration to
VF is possible. Patients with a history of syncope and an accessory
pathway capable of antegrade conduction present another indication
for curative ablation therapy.
Ventricular Tachycardia
VT presents a challenge in terms of applications of catheter ablation
techniques. The extremely variable site of tachycardia origin and the
diffuse nature of the arrhythmia circuit make localizing successful
sites for energy application difficult. Initial ablation therapy in VT was
undertaken in patients with recurrent VT and structurally normal
hearts (idiopathic VT). Catheter mapping and ablation have abolished
recurrent VT successfully with a remarkably low recurrence rate.
However, only a small portion of patients have idiopathic VT with
sustained recurrent VT. Other candidates for radiofrequency ablation
are patients with nonischemic cardiomyopathy and bundle-branch
reentry tachycardia. In these patients, ablation of the right bundle may
eliminate VT.
Patients with severe cardiomyopathy represent most patients with
recurrent VT. Patients with sustained hemodynamically stable VT and
relatively well-maintained LV function seem to be the best candidates
for mapping and ablation procedures.
Technical Aspects of Ablation Procedures
General Considerations
Before ablation procedures, the patient is prepared in a manner similar
to that for a general EPS. All antiarrhythmic drugs are discontinued.
Catheters are placed in the same manner as described earlier. When
ablations that require retrograde approach via the aorta/LV are performed, activated coagulation times (ACTs) should be monitored
regularly and full anticoagulation (ACTs >300 seconds) maintained
throughout the procedure.
In addition to standard catheters, special steerable-tip catheters
have been designed to facilitate mapping and ablation procedures
(see Fig. 6-4). They are constructed with a large platinum tip (4 to
8 mm) that can produce adequate lesion size in the endocardial
surface. An energy source is also necessary. In radiofrequency energy
ablations, a generator capable of delivering a continuous unmodulated sine wave at approximately 500 kHz is standard. These generators also continuously monitor energy output and catheter impedance.
The circuit is completed by a large indifferent skin electrode, usually
positioned in the infrascapular region on the patient’s back. A sophisticated elect rogram monitoring and storage system is necessary for
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The Electrophysiology Laboratory and Electrophysiologic Procedures 317
mapping and ablation procedures. Multiple computer-based multichannel recording systems are available that allow for real-time data
analysis and facilitate the mapping-ablation procedure. Radiologic
equipment capable of multiplane views is necessar y for optimal catheter placement.
When the patient has been prepared properly and catheters are
placed, a baseline EPS is undertaken to document the properties and
inducibility of the tachycardia. After characteristics of the tachycardia
have been evaluated fully, the mapping and ablation procedures can
begin. Techniques used in this part of the procedure are unique to the
type of tachycardia to be studied. Specific mapping techniques are
discussed here. When the optimal site for ablation has been localized,
radiofrequency current is applied to the distal pole of the mapping
catheter. Typically, current is applied during 30 to 60 seconds to
achieve a target temperature of 60° C while rhythm and intracardiac
electrograms are monitored closely (Fig. 6-30).
After ablation, there is typically a 20- to 30-minute waiting period
during which repeat EPS is undertaken. This EPS is used to document
successful ablation or signs of early recurrence. If no evidence of
recurrent tachycardia is seen during approximately 20 minutes after
ablation, the procedure can be terminated and the patient returned to
his or her hospital room. For complex procedures, the patient should
be hospitalized and observed with cardiac monitoring for approximately 24 hours after the procedure for early recurrence or new iatrogenic conduction abnormalities and procedure-related complications,
such as pneumothorax, postprocedure fever, or vascular injury associated with the ablation procedure. Patients can typically be discharged
the morning after the procedure with few physical limitations.
Atrioventricular Node Ablation
Our experience is to perform this procedure after a permanent pacemaker has been implanted. An 8-mm deflectable-tip electrode is
placed across the tricuspid annulus and positioned where a prominent
His potential is recorded. The catheter is slowly withdrawn into the
atrium (Fig. 6-31). When the ablation catheter is positioned so that
equal atrial and ventricular electrograms are recorded with a small
His potential present, radiofrequency energy can be applied. Success
is indicated by an accelerated junctional rhythm that is observed soon
after the onset of radiofrequency energy delivery and is followed by
RF current
↓ applied
I
aV
F
V
1
HBE
RVA
4.1 sec
Figure 6 -30 Loss of preexcitation (delta wave) during application of radio-
frequency current. Surface leads I, aVF, and V1 are displayed. Note the loss
of the delta wave and lengthening of the P–R inter val af ter 4.1 sec of radio frequency (RF) energy application, signifying successful ablation of the
accessory pathway. HBE, His bundle electrogram; RVA, right ventricular apex
electrogram.
V V
H
A A
Loss of
↓ preexcitation
H
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Figure 6-31 Catheter position during atrioventricular (AV) junction ablation
represented in the right anterior oblique view. The position of the His bundle
recording catheter is used as a reference. The ablation catheter is positioned on the atrial side of the tricuspid valve just below the diagnostic
catheter. (From Haines DE, Di Marco JP: Curr Probl Cardiol 27:409– 477,
1992.)
The Electrophysiology Laboratory and Electrophysiologic Procedures
AV node
Fossa ovalis
Tricuspid valve
Coronary sinus os
His bundle catheter
Ablation catheter
high-degree AV block. Immediately after AV nodal ablation, the efficacy of radiofrequency-induced AV block is approximately 95%, with
a 5% to 10% recurrence rate of AV conduction. Significant complications occur in 1% to 2% of patients. There also is a rare but recognized complication of sudden malignant ventricular arrhythmias
occurring hours to days after AV node ablation. The mechanism is
poorly understood but may be related to inhomogeneous dispersion
of repolarization. This complication has largely been eliminated by
programming the pacemaker rate to at least 90 bpm for the first several
months.
Atrial Fibrillation
Initial ablation attempts consisted of focal ablation within the pulmonary veins, which had to be abandoned because of the development
of pulmonic venous stenosis. Techniques then evolved into circumferential ablation around the ostium or antrum of the pulmonary veins,
where electrical isolation of the veins is the key endpoint (Fig. 6-32).
The procedure necessitates puncturing the interatrial septum with one
or two sheaths; comfort with this technique of trans-septal puncture
is crucial. Catheters used include multipolar circular mapping catheters. Electroanatomical mapping (CARTO 3 and NavX) to recreate the
anatomy of the atrium and pulmonary veins and guide ablation is
extremely useful and considered the norm. Its use in the treatment of
AF is mainly driven by safety considerations, such as shorter fluoroscopy and procedure times or visualization of structures that need to
be protected during the procedure. The ablation process is illustrated
in Figure 6-32. Figure 6-32, A-B, demonstrates the creation of electroanatomical maps of the LA and pulmonar y veins using technology
from the CARTO 3 or NavX systems. These images are used for ablation
in a circumferential manner around the antral regions of the veins.
The aim is to achieve electrical isolation of the veins as demonstrated
in Figure 6-32, C, where electrical silence is seen. Long-term success
rates correlate with the ability to achieve electrical isolation of all four
veins. Some of the technical challenges unique to this procedure
include (1) the need to advance two sheaths into the LA, (2) anticoagulation with heparin to keep the ACT ≥350, and (3) the need to
visualize the esophagus so as to limit the power of energy delivery
adjacent to this structure. While performing ablation on the posterior
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The Electrophysiology Laboratory and Electrophysiologic Procedures 319
LSPV
RSPV
LIPV
RIV
Angiographic CT
scan showing
identical view
CS
catheter
Esophagus image
constructed with
catheter
A
B
Figure 6- 32
along with the four pulmonar y veins. A simultaneous volume-rendered reconstructed computed tomography (CT) scan of the same structure with an
identical view as that of the NavX map is also depicted (red). Yellow dots
and lines, Locations at which radiofrequency energy applications were performed; maroon tube, reconstructed esophagus to guide energy applications
on the posterior LA wall. B, Atrial fibrillation (AF ) ablation CARTO 3. Shown
are the cranial view of the LA (teal) and four pulmonar y veins (blue, purple,
red, and green tubes) created with the CARTO 3 system. Image was created
to guide catheter ablation of AF. Maroon dots, Sites of radiofrequency energy
application to achieve electrical isolation of pulmonary veins. In this map of
the L A, no activation data are depicted. CS, Coronary sinus; LAT, lateral;
LIPV, lef t inferior pulmonary vein; LSPV, left superior pulmonary vein; RIV,
right inferior vein; RSPV, right superior pulmonary vein.
Quartet, SJM Confirm and St. Jude Medical are trademarks of St. Jude
Medical, Inc. or its related companies. Reprinted with permission of St. Jude
Medical, © 2015. All rights reserved.)
A, NavX map of the left atrium (LA; left posterior oblique view)
(A, EnSite, Velocity,
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aVF
LASO 19,20
LASO 17,18
LASO 15,16
LASO 13,14
LASO 11,12
LASO 9,10
LASO 7,8
LASO 5,6
LASO 3,4
LASO 1,2
HIS d
HIS p
ABL d
ABL
CS 9,10
CS 7,8
CS 5,6
CS 3,4
CS 1,2
RVa
C
The Electrophysiology Laboratory and Electrophysiologic Procedures
I
V
1
Figure 6- 32, cont’d
C, AF ablation. Figure demonstrates electrical isolation of the pulmonary vein achieved during catheter ablation of AF. A circumferential catheter is placed within the vein from, which 10 electrograms are
recorded (fourth through 13th tracings from the top). During circumferential
ablation per formed around the pulmonary vein ostium (similar to A and B),
from the fifth beat onward, electrical silence is seen within the vein.
I
II
III
aV
aV
aV
R
L
F
V
1
V
2
V
3
V
4
V
5
V
6
II
A
Figure 6-33 Typical atrial flutter panel. A, Typical 12-lead electrocardio-
gram (ECG). Seen are broad negative P waves with a terminal positivity in
leads II, III, and aVF. In addition, the P wave is negative in lead V6 and is
upright in lead V1.
LA wall, most operators monitor temperature in the esophagus with a
temperature probe.
Atrial Flutter
Typical atrial flutter can be recognized by the ECG, which shows broad
negative P waves with terminal positivity in leads II, III, and aV
addition, the P wave is negative in lead V
(Fig. 6-33, A). The presence of this ECG pattern almost always indicates
a reentrant arrhythmia around the tricuspid annulus, with the direction of impulse propagation occurring in a counterclockwise fashion
(see Fig. 6-33, B). The narrowest part of the circuit with the slowest
conduction properties tends to be the cavo-tricuspid isthmus, the site
targeted during catheter ablation procedures. During the ablation procedure, the catheter is dragged from the tricuspid valve to the inferior
vena cava and at each site where energy is delivered; the aim is to
achieve transmural necrosis. At the end of ablation, the electrophysiologist will look to demonstrate the presence of bidirectional conduction block across this structure. In Figure 6-33, C, conduction block is
. In
and is upright in lead V1
6
F
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The Electrophysiology Laboratory and Electrophysiologic Procedures 321
B
C
Figure 6- 33, cont’d
around the tricuspid annulus. The electrical wave front traverses around the
annulus in a counterclockwise manner, demonstrated by the color- coded
activation sequences in the electroanatomical map using the CARTO 3
system. The map shows an lef t anterior oblique (LAO) caudal view of the
right atrium (RA), tricuspid annulus, and “early meeting late,” that is, red
being adjacent to purple is very typical of a reentrant arrhy thmia. C, Electroanatomical map of the RA (L AO caudal view) and cavo -tricuspid isthmus,
demonstrating a successful ablation for atrial flutter. After ablation, pacing
is per formed from the proximal coronar y sinus (red region). The CARTO 3
map demonstrates that the electrical impulse does not traverse the
cavo-tricuspid isthmus. The achievement of conduction block across this
structure correlates with long-term success. Maroon dots, Sites in the cavotricuspid isthmus at which catheter ablation was performed.
Pacing
site
B, Typical atrial flutter is a reentrant arrhythmia
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