Address for correspondence:
Bernard Belhassen, MD Heart Institute, Hadassah Medical Center, Kyriat
Hadassah, PO Box 12000, 91120, Jerusalem, Israel
Email: bblhass@gmail.com, bblhass@hadassah.org.il
Telephone: 972.3.52.426.6856 Fax: 972.153.52.426.6856
Idiopathic ventricular fibrillation (IVF) is responsible for
approximately 5-7% of cases of aborted cardiac arrest (1). Multiple
case reports and series published during the last 70 years have shown
that short-coupled premature ventricular complexes (SCPVCs) (coupling
interval < 350ms) usually precede the onset of VF in these
patients (1-4). In a recent review, however, we found that PVCs with
“not-so-short” coupling intervals (> 350 ms)
preceded VF onset in 15 (17.4%) of 86 patients (1). Coupling intervals
ranging from 400 to 450ms were found in 5 patients. Two of these
patients had their arrhythmias originating from the right ventricular
outflow tract while the arrhythmias originated from the left posterior
fascicle, the left anterior fascicle and presumably the right
ventricular moderator band in 1 patient each (1).
In the present issue of the Journal, Surget and associates reviewed the
data from 5 French arrhythmia referral centers including 79 consecutive
patients with IVF (5). Among these patients, 12 (15.2%) had documented
late-coupled PVCs (LCPVCs) defined as PVCs falling after the end of the
T wave, with a normal QTc interval. Sustained polymorphic ventricular
tachycardia (PVT)/VF initiation by LCPVCs was documented only in 1 of
the 12 patients, whereas nonsustained (NS) PVT, couplets or single PVCs
were documented in 8, 2 and 1 patients, respectively. In 10 of 12
patients, PVCs were recorded showing both long and short coupling
intervals of 418±46 ms and 304±33 ms, respectively.
The authors should be commended for reporting these results and
especially the ECG tracings documenting these LCPVCs. We would like to
bring the following comments:
1) While the vulnerable period of the T wave has been involved in most
initiations of IVF, this study showed that LCPVCs initiating repetitive
PVCs or sustained VF had coupling intervals ranging from 360 to 500mg,
including 9 having LCPVCs > 400ms and 2 who had
LCPVCs of 500ms. In other words, the PVC falls after the end of the T
wave as attested by a coupling interval/QT ratio longer than 1 in all
patients. Although such VF initiation may look surprising, the
electrophysiologic recordings during LCPVC provided by the authors in 2
patients enable a comprehensive understanding of the underlying
mechanism which involved the Purkinje system in both cases. Two types
were identified: a) Type 1: an early Purkinje activity is conducted to
the ventricle with a long delay; b) Type 2: a late Purkinje activity is
conducted with no delay to the ventricle. A review of 10 additional
cases of the literature of LCPVCs in which electrophysiologic study was
performed confirmed that their mechanism was either of type 1 (n=4), or
type 2 (n=5), or both types (n=1) (unpublished data).
2) The definition of LCPVC used in the present paper (PVCs falling after
the end of the T wave) is different from that adopted by us (1) and
Groeneveld et al. (6) (initial PVC having a coupling interval> 350ms). The latter definition was indirectly based
on the definition of short-coupled IVF (SCIVF) (coupling interval
<350ms) made by Steinberg et al. (7). Their new definition may
be a simpler practical diagnostic tool, and mostly more accurate than
that the one currently used, especially in case of sinus tachycardia.
For example, a PVC having a coupling interval of 320ms may have less
clinical significance when the sinus cycle length is 600ms than when it
is 800ms. Harmonization and optimization of the cut-off coupling
interval for defining long and SCIVF is needed for future studies on the
topic.
3) In contrast to the IVF Dutch Registry where only 6 (19.3%) of their
31 patients with SCIVF had LCPVCs (6), 7 (70%) of the 10 patients with
SCIVF in the present study also had LCPVC. In addition, when both short
and LCPVCs were recorded in an individual, they presented a different
morphology in most cases which indicates a different ventricular exit.
In a multicenter study (58 centers and 1 multicenter, 22 countries) we
are presently conducting, which involves 287 IVF patients in whom
arrhythmia onset was documented in 231 patients, 72 (31.2%) of the
study patients showed a LCPVC initiating PVT/VF (single or couplets
LCPVCs were not accounted). Interestingly, 30 of these 72 patients also
had SCPVCs initiating VF, as found by Surget al. in their study (5).
4) In the present study, the authors found that 92% of LCPVCs were
found to originate from the left Purkinje system. In our review, we
found that in patients with long-coupled PVT/VF, there was a tendency
for higher incidence of Purkinje ectopy origin in the left ventricle
(1). Whether this is related to the complexity the left multifascicular
fiber network following the division of the left bundle branch block has
not been established.
4) In a previous study involving 83 consecutive patients with
Purkinje-initiated IVF from 4 arrhythmia referral centers, Surget and
coworkers (9) found that Purkinje extrasystoles triggering idiopathic VF
originate predominantly from the right ventricle in men and from the
left ventricle or both ventricles in women. Although not specifically
indicated, that study mainly included patients with SCIVF.
In the present study mainly dealing with LCPVC (n=12), 7 (64%) of the
11
patients with Purkinje ectopy triggering NSPVT were females and in all
these
7 patients the left Purkinje system was involved. Triggered
activities—as early afterdepolarization or delayed
afterdepolarization— are the main mechanisms of Purkinje ectopy and
well known to be increased by estradiol (9). This may explain some
increase in female prevalence. However, their predominance in the left
Purkinje system in women is unclear.
5) Idiopathic fascicular PVCs mainly originating in the left anterior
and posterior fascicles have been reported in Chinese patients (10,11).
These arrhythmias almost always consisted of single LCPVCs. They can be
ablated at usual left anterior and posterior fascicles but also in the
right coronary cusp for left anterior fascicular arrhythmias. Although
one may suspect that such arrhythmias represent the initial
manifestation of malignant Purkinjopathy, their presence has not been
reported in patients who later suffered from syncopal events or PVT/VF.
In addition, in the Chinese series, no case of syncope or sudden death
has been observed before or after ablation of the arrhythmias (10,11).
Therefore, we do recommend patient reassurance policy in asymptomatic or
mildly symptomatic patients (i.e., palpitations) displaying these
arrhythmias after extensive work-up including repeat 12 leads ECG Holter
and maybe pharmacologic drug testing as recommended by the Bordeaux
group (12). In contrast, if such arrhythmias are documented in a patient
who suffered one or more “true syncopal” events, extensive work-up
should be performed with high suspicion that the syncope might be
related to aborted malignant tachyarrhythmias. Fortunately, we have
never observed such cases in our experience.
Study limitation. A limitation of the current study is that
sustained PVT/VF initiation by LCPVCs was documented only in 1 of the 12
patients, whereas NSPVT, couplets or only single PVCs were documented in
8, 2 and 1 patients, respectively. Hence, the mechanistic and causal
relationship between LCPVCs and VF initiation remains to be further
elucidated. Albeit, this study provides further validation to the
results of the review, making it clear that not all LCPVCs are benign.
Conclusion. Documentation of SCPVCs in a VF patient who has
normal ECG and no structural heart disease, after exclusion of other
types of inherited arrhythmias, should highly suggest the diagnosis of
IVF and an arrhythmia origin in the Purkinje system. We believe that the
present study as well as the results of our review (1) should lead to
the same conclusion in case of LCPVCs, especially those suggesting a
left Purkinje origin. In other words, the value of the coupling interval
should not matter when VF is documented in the presence of normal heart.
Both “short-coupled” and “long-coupled” PVT/VF likely represent
“Purkinje arrhythmias” in the setting of “Purkinjopathy” (8) that
may be treated with ablation or quinidine (1). Further characterization
of these LCPVCs in a larger patient cohort in attempt to identify
markers of malignant arrhythmias is needed.