Radiofrequency Catheter Ablation of Ventricular Tachycardia After MI

ABSTRACT & COMMENTARY

Synopsis: Radiofrequency ablation is a useful adjunct to antiarrhythmic drug therapy and ICD therapy in patients with recurrent ventricular tachycardia.

Source: Stevenson WG, et al. Circulation 1998;98: 308-314.

Stevenson and associates describe the results of radiofrequency catheter ablation in patients with sustained monomorphic ventricular tachycardia (VT) late after myocardial infarction (MI). Data are reported from 52 patients who underwent ablation procedures between 1991 and 1995. Patients were considered to be candidates for catheter ablation if they had sustained VT that was sufficiently tolerated hemodynamically to allow catheter mapping and if there was no left ventricular thrombus present on a transthoracic echocardiogram. Most, but not all, patients had previously failed multiple attempts at antiarrhythmic drug therapy. Thirty-one percent had had previous implantation of an implantable cardioverter defibrillator (ICD). Mapping of VT was performed using criteria for entrainment previously described by Stevenson et al (J Am Coll Cardiol 1997;29:1180-1189). Attempts were made to determine the critical pathway in the reentry circuit, and ablation was performed at sites thought to be within the slow conduction zone near the exit or central or proximal sites. At sites where radiofrequency current terminated VT, additional lesions were placed immediately adjacent to the successful site. Repeat stimulation was then performed. If sustained, monomorphic VT with the same or different ECG morphology could be induced, the mapping procedure was continued.

Fifty-two patients underwent 69 mapping procedures. An average of 3.6 ± 2 different morphologies of VT were seen per patient. In only five patients was a single VT inducible. Ablation was attempted during 124 VTs. Termination of VT was seen during 74 VTs in 48 patients. The number of radiofrequency applications per procedure was 23 ± 18. The average procedure time was in excess of five hours. Procedure-related complications were noted in five patients. One patient died of acute inferior wall MI with cardiac rupture 12 hours after an ablation procedure. One patient suffered a transient ischemic event 36 hours after the ablation. Two patients required assisted ventilation during the procedure, and one remaining patient developed a femoral artery pseudoaneurysm.

Recurrent VT occurred spontaneously in the hospital before follow-up study in five patients, and an additional five patients had inducible VT at a predischarge study. Only 21 patients (40%) had no spontaneous or inducible sustained VT early after the procedure. In 16 patients (31%), VT was inducible but did not recur spontaneously before hospital discharge.

After ablation, 32 of 51 patients (63%) continued on drug therapy. Implantable defibrillators were present in 23 patients-seven of whom received their devices after the ablation.

During long-term follow-up, 10 patients died. One death was procedure-related, and two additional deaths occurred during the same hospital admission because of recurrent VT that was not controlled by ablation. There were five late heart failure deaths, one late death due to liver disease, and one late sudden death. Three additional patients underwent cardiac transplantation because of progressive heart failure. Sustained VT that was not fatal recurred in 16 patients either in the hospital before discharge (7 patients) or during follow-up (9 patients). In most cases, recurrent VT became evident early after the procedure. In 76% of the patients with recurrence, the first repeat episode was within four weeks of the ablation. Patients with more advanced left ventricular dysfunction, and patients who had previously failed antiarrhythmic drug therapy had a higher probability of recurrence. Stevenson et al conclude that radiofrequency ablation is a useful adjunct to antiarrhythmic drug therapy and ICD therapy in patients with recurrent VT. Careful selection of patients for this technically demanding procedure can provide excellent palliation, especially for patients who have repeated episodes of spontaneous VT.

COMMENT BY JOHN P. DiMARCO, MD, PhD

VT in patients with prior myocardial infarction represents a difficult challenge for electrophysiologists. Prior experience with map-directed cardiac surgery for VT in this setting had indicated that large areas of resection or ablation were required in order to achieve elimination of all ventricular tachycardias. In many patients, surgical ablation further compromised already depressed left ventricular function, and this resulted in a high short- and long-term mortality after the procedure. Radiofrequency ablation creates small discrete lesions. This is an advantage in patients with supraventricular tachycardia but makes ablation of VT much more difficult. As shown in this paper, mapping of the VT circuit is often complex, and the presence of multiple circuits limits the ability of catheter ablation procedures to eliminate all forms of VT.

However, as shown in this paper, many patients can have improvement in their clinical status with radiofrequency ablation. The procedure is most useful in those who have recurrent episodes of VT that are well tolerated. It is also interesting that in patients with an initial episode of relatively slow VT, ablation may actually provide at least a short-term cure.

The patients were entered into this study between 1991 and 1995. Since then, further refinements in ablation techniques have occurred. This has permitted the duration of the procedures to be shortened without compromising efficacy. The introduction of newer catheters that are capable of creating larger lesions and new mapping systems that may permit more rapid mapping offer great promise for the future in these patients.