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.