Outcome of endocardial resection in 33 patients with coronary artery disease: correlation with ventricular tachycardia morphology

Hybrid Catheter-Based and Surgical Techniques for Ablation of Ventricular Arrhythmias

Catheter ablation is a rapidly expanding and evolving field. The advent of interventional techniques and advances in technology have allowed catheter ablation to supplant antiarrhythmic surgery for ventricular arrhythmia treatment. However, issues related to access and energy delivery limit the use of catheter ablation in some cases. Hybrid catheter-based and surgical techniques represent a novel approach to overcome these limitations. The hybrid technique combines the strengths and minimises the limitations of either catheter or surgical ablation alone. There is a growing body of evidence in the literature supporting the safety and efficacy of the hybrid surgical technique. This review aims to provide an overview of hybrid surgical-catheter ablation for ventricular arrhythmia.

Hybrid therapies for ventricular arrhythmias

In recent years several trials demonstrated the efficacy of implantable cardioverter-defibrillation (ICD) therapy in reducing cardiac and total mortality in patients affected by rapid ventricular tachycardia (VT) and/or ventricular fibrillation. Nevertheless, ICD do not prevent arrhythmia recurrences, thus being a palliative and not a curative treatment modality. The tolerance to ICD therapy varies greatly, and within individuals, this leading to a nonuniform acceptance of this form of therapy. The very frequent occurrence of VT, defined as an arrhythmic storm, may be a life threatening condition. The majority of ICD patients is under antiarrhythmic drug therapy, to reduce episodes of VT or to make antitachycardia pacing more effective by slowing the tachycardia rate. Drug therapy, however, may cause additional problems, and does not represent the optimal solution. The prevention of VT and/or ventricular fibrillation episodes and excessive ICD therapy, remains a worthwhile goal. Radiofrequency catheter ablation (RFCA) is a curative approach, and can be expected to reduce the frequency of recurrent VT episodes in the majority of patients. The combination of these treatment modalities (ICD and RFCA) is often described as hybrid therapy, implying that the two treatments act providing some form of synergism. In experienced centers, RFCA is now performed, regardless of whether the VT rate is rapid and/or is hemodynamically unstable. Newer mapping and ablation techniques are now available, enhancing the acute success rate of the procedure. In this review the most recent application of VT catheter ablation and the use of advanced mapping and ablation techniques will be discussed.

Can catheter ablation in cardiac arrest survivors prevent ventricular fibrillation recurrence?

Ventricular tachyarrhythmias are the most common cause for sudden cardiac death. The success of catheter ablation for supraventricular tachycardias led to the supposition that ablation could also be used in the treatment of ventricular tachycardias. Despite the promising results in bundle branch reentry and some forms of idiopathic ventricular tachycardia, the success rate in patients with coronary artery disease is still low. There is hope that new approaches to reliably localize the critical region of the tachycardia and new ablation techniques to create larger areas of injury may lead to a wider application of ablation therapy in the treatment of ventricular tachycardia. Survivors of cardiac arrest typically have more rapid and unstable arrhythmias than patients with sustained ventricular tachycardia, and these rapid arrhythmias frequently degenerate into ventricular fibrillation. The instability of the arrhythmia makes it impossible to localize the arrhythmia origin with current mapping techniques. Experimental and clinical data, however, suggest that these arrhythmias also frequently start from a localized area of electrical activation. With developments in mapping techniques and energy delivery, catheter ablation may soon become a feasible therapeutic approach in some patients with unstable arrhythmias. The article discusses the prerequisites for this approach and suggests the patients who may be appropriate candidates for this technique.

Ventricular tachycardia after myocardial infarction: from arrhythmia surgery to catheter ablation

Ventricular tachycardia due to prior myocardial infarction is caused by reentry. Intraoperative mapping at the time of arrhythmia surgery has shown that the reentry circuits are diverse in size and location. Many circuits are large, extending over several square centimeters. Endocardial excision guided by activation sequence mapping, fractionated sinus rhythm electrograms, or visual identification of scarred subendocardium renders 69% to 95% of patients free from inducible ventricular tachycardia, but with an operative mortality that exceeds 8% at most centers. Catheter ablation is difficult due to limitations of catheter mapping, relatively small size of lesions produced with current techniques, and limited access to intramural and epicardial portions of the reentry circuits. Many problems need to be overcome for catheter ablation to achieve success comparable to that of surgery. At present, only hemodynamically tolerated ventricular tachycardias can be mapped. Progress is being made, and it is likely that catheter ablation will become a viable therapy for subgroups of patients with postmyocardial infarction ventricular tachycardia.

Why is catheter ablation less successful than surgery for treating ventricular tachycardia that results from coronary artery disease?

Nearly 80% of patients with coronary artery disease who have map-directed surgery for control of ventricular tachycardias require no drug therapy to prevent recurrences, while fewer than 50% of patients undergoing catheter ablation have similar outcomes. Catheter ablation will fail if arrhythmogenic sites are incompletely ablated by lesions that are too small or too far away from the reentrant pathway or if all arrhythmogenic sites are not identified. The underlying assumptions used to guide site selection are that: (a) ventricular tachycardias arise from reentrant mechanisms; (b) monomorphic ventricular tachycardias with similar QRS morphologies arise from the same pathway; (c) the ventricular tachycardia initiated during the procedure represents the patient's spontaneous arrhythmia; (d) the endocardial site that should be ablated can be identified from cardiac activation maps produced during induced ventricular tachycardia or from ancillary techniques; and (e) the patient has only one or two reentrant pathways. Relying on incorrect assumptions may account for the difference in success rates. Patients may have similar appearing ventricular tachycardias that arise from different pathways, and the entire thin layer of viable tissue between the infarct and the endocardium may contain many reentrant pathways. Some ventricular tachycardias may arise from the myocardium away from the endocardium, while others may arise from the epicardium. Small lesions may not be large enough to eliminate all possible reentrant pathways. Catheter ablation may be less successful because the lesions are inadequate, the assumptions guiding the selection of arrhythmogenic tissue are incorrect, or all arrhythmogenic sites are not identified. The primary reason catheter ablation is less successful than surgery in the treatment of ventricular tachycardias is that catheter ablation does not ablate as much tissue as is removed by surgery. The success rate of catheter ablation probably can be improved if the amount of tissue ablated is increased.

The long-term outcome of visually directed subendocardial resection in patients without inducible or mappable ventricular tachycardia at the time of surgery

INTRODUCTION

In prior studies, 20% to 40% of patients undergoing subendocardial resection (SER) for ventricular tachycardia (VT) could not be mapped intraoperatively because the VT was either noninducible or nonmappable following the ventriculotomy. The optimal surgical approach to such patients is not known.

METHODS AND RESULTS

In this study, we retrospectively compared the long-term survival and functional outcome of 29 patients with VT and prior myocardial infarction who were either noninducible or nonmappable intraoperatively and underwent a visually directed extended SER. These results were then compared to 85 patients who had inducible VT intraoperatively and underwent a map-guided sequential SER. The two patient groups had different clinical characteristics. The visually directed cohort was more likely to be male, experienced fewer VT episodes before surgery, and underwent fewer antiarrhythmic drug trials prior to resection. In addition, the visually directed group had slower VT induced at a preoperative electrophysiologic study and was less likely to present to the operating room in shock or incessant VT than the map-guided group. The postoperative VT clinical recurrence or inducibility rate was 14% in both the visually directed and map-guided groups. The long-term actuarial survival at 1, 3, and 5 years was 93%, 86%, and 75%, respectively, in the visually directed group, compared to 77%, 58%, and 58%, respectively, in the map-guided group (P = 0.06). There were no documented nonfatal recurrences of VT in either group. At 24 months following surgery, 77% of patients who had a visually directed SER were in New York Heart Association Functional Class I or II, compared to 46% of patients who underwent a map-guided SER (P < 0.05).

CONCLUSION

In patients with VT and prior myocardial infarction, the inability to induce or map the VT in the operating room does not preclude a favorable long-term outcome if a visually directed extended SER technique is used.