Endocardial and epicardial radiofrequency ablation of ventricular tachycardia associated with dilated cardiomyopathy. the importance of low-voltage scars

Study Question: How often is radiofrequency ablation (RFA) for atrial fibrillation (AF) associated with left atrial thrombi (LAT)? Methods: Phased-array intracardiac echocardiography (ICE) was used to monitor for LAT in 232 patients (mean age 55 years) who underwent pulmonary vein ostial ablation. Two 8F sheaths were positioned in the left atrium, along with an ablation catheter and a circular multipolar mapping catheter. The sheaths were continuously flushed with heparin. Heparin was administered intravenously immediately after transeptal catheterization and the activated clotting time was maintained at 250 –300 seconds. Results: LAT were observed in 24 patients (10%). The thrombus occurred prior to RFA in 50% of cases. All thrombi were either on the circular mapping catheter or a sheath. There were no thrombi on the ablation catheter or at endocardial sites of RFA. Thrombi were successfully extracted from the left atrium in 90% of cases by withdrawal of the sheath/catheter. In 2 patients, the thrombus remained attached to the left atrial septum and resolved or diminished in size after 24 hours of heparinization. No patients experienced any thromboembolic events. The only independent predictor of LAT was spontaneous echo contrast (SEC) before instrumentation. Conclusions: LAT may be common during RFA for AF, with SEC being the strongest predictor of this complication. The thrombi usually can be successfully withdrawn from the left atrium without clinical consequences. Perspective: Some investigators have reported that monitoring for the formation of microbubbles with ICE during RFA minimizes the risk of stroke. An important implication of the present study is that, because LAT are not related to RFA, monitoring for microbubbles is unlikely to reduce the risk of stroke. FM

the false negative rate would have to be very low to avoid deaths in patients who should have received an ICD. In this study, the NPV was 100%, but many of the patients did not have structural heart disease and were at very low risk of VT/VF/SCD. Before applying MTWA to clinical practice, a prospective study in a large number of high-risk patients is needed. FM

Endocardial and Epicardial Radiofrequency Ablation of Ventricular Tachycardia Associated With Dilated Cardiomyopathy. The Importance of Low-Voltage Scars Soejima K, Stevenson WG, Sapp JL, Selwyn AP, Couper G, Epstein LM. J Am Coll Cardiol 2004;43:1834 – 42. Study Question: What is the significance of low-voltage scars in patients with dilated cardiomyopathy (DCM) undergoing radiofrequency ablation (RFA) of ventricular tachycardia (VT)? Methods: Sinus rhythm voltage maps were created with a 3-dimensional electroanatomical mapping system in 28 patients with DCM referred for RFA of monomorphic VT. Scars were identified by a voltage ⬍1.5 mV. Appropriate ablation sites were identified by entrainment and pace mapping. Mapping was performed endocardially in 26 patients and epicardially in 8 patients. Results: Eighty-two VTs were induced in the 28 patients, and 89% were due to myocardial re-entry, 8% were focal and 3% were caused by bundle-branch re-entry. Among the patients with ventricular re-entry, scar was identified in 20 of 20 patients who underwent endocardial mapping, and in 7 of 7 patients who underwent epicardial mapping after unsuccessful endocardial mapping. All re-entry circuit isthmuses were bounded by either an endocardial or epicardial scar. Epicardial RFA resulted in the noninducibility of VT in 6 patients. At a mean follow-up of 11 months after RFA of the VTs, 54% of the patients with ventricular re-entry were free of recurrent VT. Conclusions: The most common cause of monomorphic VT in patients with DCM is ventricular re-entry associated with scar. If endocardial mapping and/or RFA are unsuccessful, an epicardial approach is likely to be useful. Perspective: This study demonstrates that mapping and ablation of VT within the pericardial space is worthwhile in patients with DCM. However, the long-term success rate of only 54% suggests that the re-entry circuits often may lie deep within the myocardium, making them difficult to eliminate by RFA. FM

Radiofrequency Catheter Ablation of Type I Atrial Flutter Using Large-Tip 8- or 10-mm Electrode Catheters and a High-Output Radiofrequency Energy Generator Feld G, Wharton M, Plumb V, Daoud E, Friehling T, Epstein L. J Am Coll Cardiol 2004;43:1466 –72. Study Question: How safe and effective are large-tip radiofrequency ablation catheters when used to treat patients with typical atrial flutter (AFl)? Methods: Radiofrequency ablation of the cavotricuspid isthmus (CTI) was attempted in 158 patients with typical AFl using an 8- or 10-mm-tip ablation catheter and a maximum output of 100 watts. The mean age of the patients was 61 years and 28% had right atrial enlargement. All patients were followed for ⱖ6 months. Results: Complete block in the CTI was achieved acutely in 93% of patients, with a mean procedure time of 2 hours and a mean ablation time of 39 minutes. There was no difference in success rates between the 8- and 10-mm-tip catheters.

Left Atrial Thrombus Associated With Ablation for Atrial Fibrillation: Identification With Intracardiac Echocardiography Ren JF, Marchlinski FE, Callans DJ. J Am Coll Cardiol 2004;43: 1861–7.

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