Safety and outcomes of ablation
The presence of a mechanical mitral valve for VA ablation can pose unique operative risks. Strict attention with respect to periprocedural anticoagulation is required to minimize the risk of thromboembolism or valve thrombosis. In addition, meticulous care is required when mapping around the valve to avoid catheter entrapment. We typically avoid use of a multispline 37 catheter in patients with mechanical valves due to the risk of entrapment and device shearing. In addition, use of ICE is strongly encouraged to help more accurately determine anatomical locality. In addition, fluoroscopic imaging in the right anterior oblique plane would help provide information regarding proximity to the mitral valve. In the rare and potential catastrophic event of catheter entrapment during mapping or ablation, management includes cautious catheter rotation/ manipulation in various planes to free up the catheter. Advancement of a support sheath up to the level of obstruction can be entertained. Furthermore, measures to prolong mitral valve opening such as rapid ventricular pacing and adenosine (which prolong diastole) can be attempted.38 If these measures fail, one can employ extraction techniques or ultimately consider surgical removal.
Thromboembolic events are uncommon, yet devastating complication of VT ablation. Ventricular ablation is associated with an inherent risk of thrombus formation with thrombus size directly proportional to ablative lesion size.39 Reported incidence of stroke/ TIA with VT ablation ranges from 0.8% to 1.8%.40,41 Studies have shown that the incidence of thromboembolic events with VT ablation is higher in patients with structural heart disease.42In our study, no thromboembolic events or other procedure-related complications were reported. ICE was performed before and after the ablation did not detect any change of valve function or development of pericardial effusion. Ecktar et al reported a series of VT ablation in 20 patients including 8 patients with MVS.10 In their study, during a median follow-up of 2.1 years, 11(55%) patients remained free of spontaneous VT. Three patients had repeat ablation due to recurrent VT. In our study, the overall VA recurrence-free rate at 1-year was 13/18 (72.2%). We also found that MVS patients with a history of CAD showed a trend of better VA recurrence-free survival compared with those without CAD history. (Figure 2B ) This could be related to the previously reported different nature of VT circuits between ICM and NICM. 43,44 One observational study compared the characteristics and the outcomes of VT ablation between ICM and NICM patients has shown that complete success and 1-year VT-free survival were higher in the ICM group.44 The critical isthmus for VT was identified with endocardial entrainment in 62% of the ICM group and in 17% of the NICM group. The lower likelihood of identifying the isthmus in NICM might be related to a midmyocardial or epicardial location, which is a less amenable location for successful ablation especially in patients with previous cardiac surgery.