Ablation for Ventricular Tachycardia
May 1, 2000
Ablation for Ventricular Tachycardia
abstract & commentary
Synopsis: Radiofrequency linear endocardial lesions can be used to disrupt ventricular tachycardia circuits in patients with ventricular tachycardia that cannot be mapped by standard techniques.
Source: Marchlinski FE, et al. Circulation 2000; 101:1288-1296.
Marchlinski and colleagues report a new technique for catheter ablation of ventricular tachycardia (VT). Sixteen patients comprised the study group. All had frequent episodes of rapid monomorphic tachycardia that had led to multiple implantable cardioverter defibrillator (ICD) shocks. All patients had failed multiple drug trials and six had failed prior ablation attempts. These 16 patients constituted one-third of the patients referred to Marchlinski et al’s laboratory for catheter ablation of VT during the study period.
Nine patients had VT in the setting of prior myocardial infarction (MI) and seven had nonischemic cardiomyopathy. Patients were taken to the electrophysiology laboratory and underwent detailed voltage mapping during sinus rhythm. Only the left ventricle was mapped in patients with prior MI, but both the right and left ventricles were mapped in patients with nonischemic cardiomyopathy. Three patients had mapping and ablation performed using a standard thermistor ablation catheter. The next 13 patients underwent mapping using a magnetic mapping system (CARTO, Biosense, Inc.) that allows electroanatomic confirmation of catheter position in three dimensions. Reference values for electrogram amplitude were established for distinguishing between normal and abnormal electrograms using both systems. After determination of the area of interest, linear lesions were placed across the borders of the endocardium that demonstrated abnormal electrogram voltage, and through border zones at sites where pace mapping approximated the electrocardiographic wave (QRS) morphology of VT. Ablation was performed using sequential point lesions to create linear ablation lines. This was done using fluoroscopic guidance in the first three patients and using three-dimensional magnetic mapping in the last 13. Programmed stimulation was performed at the end of the procedure. VT recurrences during clinical follow-up were identified by device interrogation and/or report of symptoms.
The number of endocardial sites mapped was more than 200 in all patients. Large areas with abnormal electrograms were present in both patients with coronary artery disease (CAD) (65 ± 24 cm2) and in the right ventricle of those with nonischemic cardiomyopathy (60 ± 36 cm2). A median of 55 radiofrequency lesions was applied per patient. These were used to create one to nine (median, 4) linear lesions. The average length of the linear lesion was 3.9 cm with a range of 1.4 to 9.4 cm. Linear ablation was effective in suppressing all inducible VT acutely in seven of 15 patients. The induced VTs in the remaining patients matched the cycle length or morphology of the clinical arrhythmia in five patients and was different in three. Procedure time ranged from six to 13.5 hours. There was no significant change in left ventricular ejection fraction in six patients who had measurements before and after ablation. One patient experienced a cerebral vascular accident at the end of the procedure.
The minimum period of follow-up was three months. Three of the 16 patients died at three, four, and eight months after the procedure from refractory heart, pneumonia, or complications of abdominal surgery. Fifteen of 16 patients remained free of VT during the initial follow-up month and 12 of 16 patients have been free of any recurrent VT during the entire follow-up period.
Marchlinski et al conclude that radiofrequency linear endocardial lesions can be used to disrupt VT circuits in patients with VT that cannot be mapped by standard techniques. Electroanatomic mapping aids in the placement of these lines.
Comment by John P. DiMarco, MD, PhD
The current standard approach for mapping and ablation of VT in patients with prior MI or ischemic cardiomyopathy involves induction of the tachycardia and subsequent entrainment mapping. Entrainment mapping requires a tachycardia that does not produce severe hypotension or hemodynamic collapse since the patient must remain in tachycardia for long periods to allow the catheter manipulation and pacing to generate an entrainment map. Only a small fraction of patients with VT can tolerate this procedure and this has limited the application of ablation therapy in patients with VT and structural heart disease. The procedure outlined by Marchlinski et al provides an alternative approach in these patients.
The concept underlying this procedure is reminiscent of the surgical approaches previously used in patients with VT and coronary artery disease (CAD). The subendocardial resection approach involved resection of all visible scar and was associated with an arrhythmia cure rate of 70-80% even if little or no intraoperative mapping was performed. However, the amount of surgery required often was extensive. This produced an adverse effect on ventricular function, and late heart failure was common. As ICD therapy has improved, the frequency of this type of surgery has declined. The encircling endocardial ventriculotomy tried to use a near full thickness excision around the area of scar to control VT. This operative approach has also largely been abandoned due to adverse effects on ventricular function. The approach described here seems to produce the same electrical results as those two surgical procedures without the expense of surgery and without producing any significant deterioration in hemodynamic function.
The electroanatomic mapping technique certainly was helpful for guiding the placement of the lesions. However, this technique still involves mapping a large number of individual points. This requires long periods of catheter manipulation and increases the risk of the procedure. Alternate approaches using either noncontact mapping or basket mapping of an entire chamber might allow the voltage maps necessary to locate the densely scarred areas to be generated more quickly. The major time requirement then would be for placement of linear lesions. Catheter designs now being tested for linear ablation of atrial fibrillation might also be helpful here. Further development of these catheters has the potential to shorten the time for these procedures.
The results reported by Marchlinski et al are impressive. It remains to be seen whether this technique can be streamlined and made applicable to larger numbers of patients. The combination of ICD therapy for disorganized arrhythmias and an ablation technique such as this for organized but previously unmappable tachycardias would be a major advance.
Which approach shows promise for catheter ablation of VT?
a. Entrainment mapping during VT
b. Electroanatomic magnetic mapping
c. Fluoroscopy to detect aneurysms
d. All of the above
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