3. Discussion
We described the case of a patient with refractory VT secondary to LVA,
whose treatment with unipolar RFCA was ineffective; consequent CABG with
bipolar RFCA assisted by CARTO mapping resulted in good postoperative
outcomes.
RFCA is the main treatment for refractory VT caused by an MI scar. A
retrospective study by Heart Rhythm reported on 365 patients with MI
complicated with LVA who were treated by RFCA. The results showed that
the mortality rate of patients with MI scar area larger than 20% was
still 25% one year after successful RFCA. Baseline data analysis of
selected cases showed that less than half of the patients underwent CABG
before RFCA.1 It is suggested that if myocardial
ischemia is not effectively ameliorated, the risk of malignant LVA after
MI is limited by RFCA alone. Also, because the electrophysiological
matrix of LVA complicated with LVA can be located in the sub-epicardium
and endocardium, as well as in the epicardium, it is difficult to
achieve the transmural effect of RFCA in the endocardium alone and,
thus, its curative effect is limited. The patient underwent endocardial
unipolar RFCA assisted by a cardiologic CARTO mapping system before
surgery, which did not effectively curb refractory VT. Hence, we
considered three main reasons: 1. The reentrant circuit is not only
located in the endocardium but also the epicardium and/or
sub-epicardium; 2. The unipolar RFCA pen cannot achieve true wall
penetration; 3. The myocardial ischemia of the patient’s left
ventricular anterior wall has not been solved.
CABG is the preferred treatment for patients with persistent VT caused
by the left main coronary artery stenosis and/or multiple vessel
lesions. At present, the main surgical treatment for LVA is CABG
combined with LVA formation. However, the 2011 AHA guidelines for CABG
clearly highlighted that CABG could only effectively reduce ventricular
fibrillation/tachycardia caused by myocardial ischemia. However, it does
not reduce all factors leading to VA, especially the lack of clinical
evidence for the efficacy of patients with VT caused by scarring after
myocardial ischemia and necrosis.3Chiriac et al.4retrospectively analyzed the cure rate of ventricular arrhythmia in 765
patients with coronary heart disease complicated with potential
malignant ventricular arrhythmia after coronary revascularization and
simple antiarrhythmic therapy. The study showed a nearly 50% incidence
of potential malignant ventricular arrhythmia, even after coronary
revascularization and drug treatment. The absence of statistically
significant differences between the two groups suggested that scar
reentry may occur. It plays an important role in LVA with ventricular
arrhythmia. The preoperative CARTO mapping system showed that the first
form of LBBB VT was related to intraventricular aneurysm reentry, and
the second form of RBBB VT was related to the reentry of the junction
between normal left ventricular anterior myocardium and the edge of LVA.
Therefore, simple CABG and LVA formation do not effectively curb the
refractory VT produced by the reentrant circuit.
Applying implantable cardioverter defibrillators (ICD) is the most
effective method to prevent sudden cardiac death.3However, the European ESC/EACTS Guidelines for Coronary
Revascularization in 2014 recommend that ICD implantation within 2 years
after coronary revascularization does not effectively reduce the
incidence of sudden death.5 Survival curves of 882
patients with and without ICD after CABG were retrospectively
analyzed.6 The results showed that there was no
significant difference in the mortality rates between patients with and
without ICD within 2 years after CABG. Our patient had 20 to 40 episodes
of VT every day before surgery, and all needed electro-cardioversion. If
ICD was implanted, pacing of ICD caused by refractory VT would cause
immense mental and physical pain to this patient.
LVAs form after acute MI and there are relatively viable muscle islands,
necrosis, and fibrous tissues at the junction of normal myocardial
tissue and scar tissue of LVA, which constitute a complex interlaced
marginal zone, thus changing the original conductivity and refractory
period of myocardial cells, leading to inconsistent repolarization of
myocardial cells, asynchronous conduction through abnormal pathways, and
a ventricular ectopia impulse. Among them, the ectopic origin and a
reentrant circuit are considered as the primary electrophysiological
basis of ventricular arrhythmia. The ectopic origin can be located in
possible areas, such as the endocardium, a few in the epicardium and
sub-epicardium, or even in the interventricular septum and papillary
muscle. The successful rate of ablation for the earliest ventricular
excitation was only 25%.7 However, no matter how the
location and number of ectopic origins change, the abnormal electrical
impulse will pass through the reentrant circuit formed by LVA, leading
to VT.8 Therefore, the restraint and destruction of
reentrant circuit plays a key role in the treatment of ventricular
arrhythmia complicated with VT.
We have attempted to treat
patients with ventricular arrhythmia caused by LVA via surgery combined
with epicardial unipolar RFCA since 2009.9 The result
has proven that the treatment of LVA with ventricular arrhythmia from
the cardiac electrophysiology had important clinical significance.
However, intraoperative and postoperative examinations showed that
ventricular arrhythmias of some patients were not effectively
suppressed, suggesting that due to technical limitations, it is
impossible to achieve complete transmural ablation of the endocardium
and epicardium. Not only the ablation effect is not ideal, but also a
new ectopic origin or reentrant pathway may be created between
endocardial and epicardial undergo radiofrequency ablation. Therefore,
exploring effective surgical electrophysiological therapy has become a
bottleneck in the treatment of LVA. The key to bipolar RFCA is stable
power, easy operation, and the power is automatically cut off when the
ablation reaches the wall penetration, which could ensure an optimal
transmural effect. It can also be used under beating-heart
conditions.10 Determining the range of bipolar RFCA is
necessary. The location of the LVA and isthmus mapped by CARTO
effectively determines the anatomical location of the reentrant circuit
and the scope of subsequent ablation.1 The procedure
used in the present case effectively decreased refractory VT caused by
LVA.
The methods determining the range of radiofrequencies for LVA ablation
with bipolar RFCA forceps are significant. In endocardial RFCA,
intracardiac ultrasound was used earlier to accurately determine the
anatomical location of LVA. Second, the excitation, traction mapping,
and voltage mapping were performed at the onset of VT and sinus rhythm,
respectively. Further, the locations of LVA and isthmus were determined,
and the isthmus was ablated, and LVA isolated. However, viable
myocardium may remain in the LVA and its margin, and VT may still occur
after primary unipolar RFCA due to myocardial edema after local
ablation. However, in our case, the full reconstruction and measurement
of the endocardial surface effectively guided the surgeon to determine
the anatomical location of the reentrant circuit produced by LVA and
provided an important reference for the location and scope of subsequent
ablation. We used 8 RFCA lines with the LVA as the center and the
ablation margin, at least around the myocardium. One of the RFCA lines
passed through the key isthmus of the VT reentrant circuit mapped by the
CARTO system to cut off the separate reentrant circuit formed by the LVA
to the greatest extent. The results of the one-year follow-up showed
that this method was effective.