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Teaching Rounds in Cardiac Electrophysiology
Unusual Incessant Ventricular Tachycardia
What Is the Underlying Cause and the Possible Mechanism?
Jayaprakash Shenthar, MD, DM
V
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entricular tachycardia (VT) is defined as a tachycardia
with a rate of >100 per minute, with ≥3 consecutive beats
that originates from the ventricles, and is independent of atria or
atrioventricular nodal conduction. Of all the VTs, 10% occurs
in those with structurally normal heart and these are called as
idiopathic VTs, and the rest 90% occurs in patients with structural heart disease. VTs may be classsified based on the clinical
characteristic (clinical VT, hemodynamically stable or unstable,
repetitive, incessant, etc.), morphology (monomorphic, multiple morphologies, pleomorphic, polymorphic, bidirectional,
etc.) or mechanisms (scar-related reentry, automaticity, and
triggered activity). Incessant VT is defined as continuous sustained VT during several hours, which recurs promptly despite
repeated intervention for termination. VT storm is considered
as ≥3 separate episodes of sustained VT within 24 hours, each
requiring termination by an intervention. Monomorphic VT has
a uniformly similar QRS configuration from beat-to-beat, with
either right or left bundle configuration depending on whether
the dominant deflection in lead V1 is R or S wave. Multiple
monomorphic VTs refer to >1 morphologically distinct monomorphic VT, occurring as different episodes, or induced at different times. Polymorphic VT has continuously changing QRS
configuration from beat-to-beat indicating a changing ventricular activation sequence. Pleomorphic VT has >1 morphologically distinct QRS complex occurring during the same episode
of VT, but the QRS is not continuously changing. Bidirectional
VT (BVT) is characterized by beat-to-beat alternation of the
QRS axis on the ECG and is usually regular.1
transition alternating from V3 to V6, and evidence of atrioventricular dissociation (Figure 1). Tachycardia was unresponsive
to intravenous lignocaine, esmolol, amiodarone (300 mg during
1 hour), and 2 attempts of biphasic direct current (DC) cardioversion of 200 J. Because the tachycardia was incessant, patient
was sedated, intubated, ventilated, and continued on intravenous
amiodarone (900 mg/24 hours) with further 4 unsuccessful
attempts at DC cardioversion. Tachycardia converted to monomorphic VT with occasional VT complexes of the 2nd morphology (Figure 2), which terminated 6 hours later while on infusion
of amiodarone and lignocaine, and while he was being considered for radiofrequency catheter ablation. ECG in sinus rhythm
was essentially normal (Figure 3), chest x-ray revealed superior
mediastinal widening (Figure 4A), and echocardiogram showed
normal left ventricular function. Cardiac MRI was performed,
which revealed focal areas of thickening and increased signal
intensity on T2-weighted images. Early gadolinium enhancement was seen in the mid interventricular septum, anterolateral
and anteroinferior walls, with the lesions having a target appearance with peripheral slightly hyperintense rim and central hypo
intensity (Figure 4B). Delayed gadolinium enhancement was
found predominantly in the midmyocardium and epicardial
in basal and lateral segments of the left ventricle. 18F-fluoro2-deoxy-d-glucose (FDG) positron emission tomography scan
revealed basal and midanteroseptal perfusion defect with intense
FDG uptake in these regions suggestive of myocardial inflammation along with evidence of inflammation in the paratracheal
lymph nodes (Figure 4C). Serum biochemistry was normal
including serum calcium, serum angiotensin-converting enzyme
(ACE), digoxin, blood aconite levels (report received 2 weeks
later), and IgG and IgM assays were negative for tuberculosis
bacilli. Transbronchial lymph node biopsy revealed noncaseating granulomas suggestive of sarcoidosis (Figure 4D). Patient
was initiated on 1 g of methylprednisolone (Solumedrol) per day
for 3 days intravenously and amiodarone infusion of 1 g/d was
continued for 3 days after which it was switched to oral therapy
and patient was extubated after 36 hours. Later, oral predinsolone was initiated at 60 mg/d for 2 months and was tapered to
a maintenance dose of 10 mg/d for 2 years and stopped after
a normal repeat positron emission tomography FDG scan. A
single chamber implantable defibrillator was implanted after 5
days of VT-free interval. Device-based testing was performed at
a single drive train of 600 ms and ≤2 extrastimuli which did not
induce the VT and a single shock at 14 J terminated induced VF.
Editor’s Perspective see p 1512
Here, we describe unusual incessant VT in a young male and
discuss evaluation, management, and the possible mechanism.
Case Report
A 33-year-old male, nondiabetic, nonhypertensive, presented
with history of palpitation, chest discomfort, and fatigue of 6
hours duration. He had been otherwise healthy, not on any
medications with no history of tobacco, alcohol, or drug use.
At presentation, pulse rate was 144 beats per minute, irregular,
blood pressure 96/60 mm Hg, and the rest of physical examination was unremarkable. Twelve-lead ECG revealed a wide
complex regularly irregular tachycardia at a rate of 144 beats
per minute, right bundle morphology, QRS duration of 200 to
220 ms, QRS axis alternating between +160° and −40°, QRS
Received February 14, 2015; accepted May 20, 2015.
From the Department of Cardiology, Sri Jayadeva Institute of Cardiovascular Sciences and Research, Bangalore, India.
Correspondence to Jayaprakash Shenthar, MD, DM, Electrophysiology Unit, Department of Cardiology, Sri Jayadeva Institute of Cardiovascular
Sciences and Research, 9th Block Jayanagar, Bannerghatta Rd, Bangalore 560069, India. E-mail [email protected]
(Circ Arrhythm Electrophysiol. 2015;8:1507-1511. DOI: 10.1161/CIRCEP.115.002886.)
© 2015 American Heart Association, Inc.
Circ Arrhythm Electrophysiol is available at http://circep.ahajournals.org
1507
DOI: 10.1161/CIRCEP.115.002886
1508 Circ Arrhythm Electrophysiol December 2015
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Figure 1. Twelve-lead ECG showing bidirectional ventricular tachycardia. Two morphologies of QRS complexes, namely A and B, with A
to A interval being 72 beats per minute and B to B interval of 72 beats per minute, making up the tachycardia rate of 144 beats per minute. The relationship of A to B interval is constant at 0.56 s and B to A interval is constant at 0.32 s.
Amiodarone was tapered and stopped after 6 months. Genetic
testing for possible catecholaminergic polymorphic ventricular
tachycardia with analysis for 4 genes: RYR2, CASQ2, ANK2,
and KCNJ2 were negative (report received after 2 months). Four
years later, patient has not had any device activation and has normal left ventricular function.
Discussion
This case describes an unusual presentation of isolated cardiac
sarcoidosis with incessant regularly irregular BVT, normal LV
function, and no conduction system involvement as the initial
manifestation. Clinical manifestations of cardiac sarcoidosis
are dependent on the location, extent, and activity of the disease. The 3 principal sequelae of cardiac sarcoidosis are (1)
conduction abnormalities (2) ventricular arrhythmias, and
(3) heart failure.2,3 Cardiac sarcoidosis usually presents with
monomorphic VT or conduction system disturbances. Macroreentry around areas of granulomatous scar is the commonest
mechanism of VT in sarcoidosis.4
BVT is a rare ventricular tachyarrhythmia. It is usually regular, demonstrates a beat-to-beat alternation of the
QRS frontal axis varying between −20° to −30° and +110°.
Tachycardia rate is typically between 140 and 180 beats per
minute and the QRS is relatively narrow with duration of 120
to 150 ms. There are many causes of BVT described in the
literature5–10 (Table). Although the most characteristic ECG
pattern of BVT is right bundle branch block with an alternating QRS axis,9 other patterns such as alternating right bundle
branch block and left bundle branch block, or alternating
QRS axis with a narrow QRS,11 have also been observed. Few
arrhythmias have been subject to such different hypothesis
about the mechanism and it has fascinated electrocardiographers for many decades.
Postulated mechanisms have included a single focus in the
proximal His bundle or bundle branches with alternating left
fascicular block, or single or double foci in the distal His purkinje system and also reentry.10,12,13 Recently, Ping-Pong mechanism or reciprocating bigeminy in the distal his purkinje system
because of delayed after depolarization has been proposed as
the mechanism for BVT. It was shown that when the heart rate
exceeded the threshold for bigeminy at the first site in the His–
Purkinje system, ventricular bigeminy developed, causing the
heart rate to accelerate and exceed the threshold for bigeminy
at the second site. Thus, the triggered beat from the first site
induced a triggered beat from the second site and vice versa.14
BVT in present case has many unusual features. The QRS
duration is broad at 200 to 220 ms, unlike cases of in most
BVT where it is relatively narrow at 120 to 150 ms. Wide QRS
in this case possibly indicates intramyocardial/epicardial site
of origin, unlike the usual BVT where the origin is supposedly
more closer to the His purkinje system. In an elegant experiment using arterially perfused canine wedge preparations
with transmural ECG and action potentials recorded simultaneously from epicardial, M, and endocardial cells epicardial
origin of BVT has been demonstrated.13
The most intriguing feature is the regularly irregular
rhythm as seen in Figure 1. A careful analysis of relationship
between the 2 morphologies of QRS complexes namely A and
B reveals that the A–A interval is 72 beats per minute (0.88
s) and B–B interval is 72 beats per minute (0.88 s), resulting
in tachycardia rate of 144 beats per minute. The relationship
of A to B interval is constant at 0.56 s, and B to A interval is
constant at 0.32 s, and this relationship is constant throughout
the tachycardia resulting in a regularly irregular rhythm. The
broad QRS, with axis alternating between +160° and −40°,
transition alternating from V3 to V6 in chest leads, possibly
Shenthar Incessant Ventricular Tachycardia 1509
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Figure 2. Twelve-lead ECG showing partial suppression of suppression of focus A resulting in occasional ectopic beats during sustained
monomorphic ventricular tachycardia (VT) because of focus B. Measurement of B–B intervals shows that there is doubling of the rate
from 0.88 s during bidirectional VT (BVT) as seen in Figure 1, compared with 0.44 s during monomorphic VT suggesting parasystole as
the mechanism for the arrhythmia.
indicates 2 independent foci. The original hypothesis of dual
ventricular foci firing alternatively that was suggested as
the mechanism was discarded because of the constant R–R
interval that would presuppose a perfect alteration of the 2
foci.12 However, in this case, regularly irregular rhythm can
be explained by automatic firing of 2 different foci at constant
intervals and presence of entrance block in each of the foci
akin to a dual parasystole.
Parasystole refers to those instances of double rhythm of
the atria, atrioventricular junction or ventricles in which 1 pacemaker is protected from the impulses of the other.15 Parasystole
requires an area of focal impulse formation which is surrounded
by an area that protects (shield) the focus from external impulses
thus resulting in an entry block but no exit block of the focus.
Automaticity and protection are the hallmarks of parasystole.
This feature lead to the diagnostic triad of classical parasystole,
Figure 3. Twelve-lead ECG in normal sinus rhythm with no evidence of conduction delay.
1510 Circ Arrhythm Electrophysiol December 2015
Figure 4. A, Chest x-ray PA view: showing mediastinal widening. B, T2-weighted cardiac MRI: showing gadolinium enhancement in mid interventricular
septum (arrow). C, 18F-fluoro-2-deoxy-d-glucose
(FDG) positron emission tomography scan: showing basal and midanteroseptal perfusion defect
with intense FDG uptake. D, Transbronchial biopsy:
showing noncaseating granulomas.
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that is, varying coupling intervals of the ectopic focus, mathematically related interectopic intervals and the presence of fusion
beats.16 The original assumption of total independence (protection) of parasystolic focus from extraneous beats is no longer
considered true. It is now evident that any pacemaker connected
to the surrounding tissues by an area of depressed excitability
producing entrance conduction disturbances while allowing the
impulses to exit is subject to some degree of modulation by electrotonic depolarizations arising in the surrounding tissues, that is,
depolarization of the surrounding field will induce a partial depolarization of the pacemaker cells. This results in the occurrence
of modulated parasystole.17,18 This means that nonparasystolic
beats falling close to the parasystolic beats can cause (1) maximal delay, (2) maximal acceleration, (3) lesser effects, (4) practically no effect, or (5) pacemaker annihilation of the parasystolic
focus.16,19 Nonparasystolic beats falling during the first half of the
parasystolic interval induce a prolongation of this interval, those
occurring during the second half of the parasystolic cycle length
cause an abbreviation of this interval. The electrotonic modulation (causing either prolongation or shortening of the parasystolic
cycle length) is maximal at the middle point of the parasystolic
interval.19 Thus, the coupling interval of the ectopic focus may
not be constant in modulated parasystole and interectopic interval
may also show variation. Modulation may also cause coupling
intervals to be fixed, and the fixed coupling intervals may suggest
a reciprocating bigeminy. It has been shown that if the impedance of the communication between the ectopic focus and the
surrounding ventricle is low, locking of the ectopic pacemaker
could be nearly fixed to give the appearance of a reciprocating
bigeminy.18 This is substantiated by Figure 2 in our case, wherein
after infusion of amiodarone there is partial suppression of focus
A resulting in occasional ectopic beats during sustained monomorphic VT because of focus B. Measurement of B–B intervals
shows that there is doubling of the rate from 0.88 s during BVT
as seen in Figure 1, compared with 0.44 s in Figure 2 suggesting
a parasystole as the mechanism of arrhythmia. The interlocking
of the beat A to beat B still persists. But measurement of intervals
between A–A in this strip does not show a mathematical relation
relationship, which can be explained by modulation of parasystole focus A by the preceding beat (from focus B). El-Sherif et al20
have described concurrent discharge of a 2 to 6 parasystolic foci
with a total of 24 parasystolic foci in the 6 patients with advanced
heart disease. It is now accepted that irregularity of ectopic is the
rule rather than an exception.16
It is now evident that parasystole may give rise to various rhythm patterns. Parasystolic accelerated idioventricular
rhythm–producing BVT has been described in digitalis toxicity.21 In the present case, dual parasystole is the most plausible
explanation. The occurrence of only occasional beats of focus
A (Figure 2) where the focus B is continuing in an accelerated rate excludes the possibility of a BVT because of a pingpong effect as there is no consistency in occurrence of focus
Table. Causes of Bidirectional VT5–10
Digitalis toxicity
Hypokalemic periodic paralysis
Andersen–Tawil syndrome
Fulminant myocarditis
Catecholaminergic polymorphic ventricular tachycardia syndrome
Aconite poisoning
Left ventricular noncompaction
VT indicates ventricular tachycardia.
Shenthar Incessant Ventricular Tachycardia 1511
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A, which should have regularly alternated with focus B, if it
was because of ping-pong effect.
Triggered activity and abnormal automaticity have been
described secondary to myocardial inflammation in myocarditis.8,22 Incessant nature of the tachycardia, unresponsive to
multiple DC cardioversion, antiarrhythmic agents such as
β-blockers and lignocaine, suggests that the possible mechanism of VT is enhanced automaticity because arrhythmias
either because of reentry or because of delayed after depolarization typically are responsive to these maneuvers.23 It is
possible that local inflammation around the automatic foci
could create an entry block in cardiac sarcoidosis, resulting
in parasystole. Multiple areas of granulomatous inflammation
which is not uncommon in cardiac sarcoidosis could allow 2
parasystolic foci to coexist as in the present case. The mechanism of BVT is thought to be because of elevated intracellular
calcium causing delayed after depolarization in anatomically
separate parts of the conducting system.23 One possible explanation is that the inflammation causes cells from damaged
areas to cause spontaneous release of Ca2+ from sarcoplasmic
reticulum, which could generate waves of intracellular Ca2+
elevation and arrhythmias.
To the best of our knowledge in patients with cardiac sarcoidosis, BVT particularly irregularly irregular VT has not
been described. This adds another differential diagnosis for
this intriguing VT.
Conclusions
Cardiac sarcoidosis should be considered in the differential
diagnosis of patients presenting with BVT, especially if the QRS
is broad, the rhythm irregular and tachycardia incessant. Dual
parasystole may be a possible mechanism in some cases of BVT.
Disclosures
None.
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Key words: heart ◼ sarcoidosis ◼ ventricular tachycardia
Unusual Incessant Ventricular Tachycardia: What Is the Underlying Cause and the
Possible Mechanism?
Jayaprakash Shenthar
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Circ Arrhythm Electrophysiol. 2015;8:1507-1511
doi: 10.1161/CIRCEP.115.002886
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