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Removing the Blindfold: Cardiac MRI Prior to Repeat Ablation of Ventricular Tachycardia

Myocardial scar is the most common substrate for ventricular tachycardia (VT) in the setting of underlying cardiomyopathy (CMP). Cardiac magnetic resonance imaging (CMR) is a key imaging modality that can characterize the extent and location of scar and has been shown to be useful in guiding the initial ablation of ventricular tachycardia.1,2 In this issue of the Journal, a study by Njeim et al. further examined the usefulness of employing CMR to guide the repeat ablation strategy in patients with a prior failed endocardial ablation of VT.3 The study included 20 patients and the ratio of nonischemic CMP to ischemic CMP was 3:2. The study subjects were predominantly men in their 60s with mild to moderate left ventricular systolic dysfunction and a significant VT burden: a third each with syncope or VT storm and two-thirds with recurrent VT shocks (averaging 6 shocks in 6 months) after failing one or more anti-arrhythmic medications. Importantly, half the patients underwent CMR with an implantable cardioverter defibrillator (ICD) in place (of these, 1 was pacemaker dependent and another had an abandoned RV pacing lead) while the other half received an ICD after the CMR. The 3D endocardial CMR maps were registered with the electroanatomical maps and a standard endocardial or epicardial mapping/ablation procedure was subsequently performed with the approach determined by the predominant CMR scar location. CMR determined an endocardial approach in half the patients (endocardial scar (n = 7) and septal/intramural scar (n = 3). An epicardial approach was performed in the remaining (epicardial scar = 5, intramural free wall scar = 4), except for a patient with significant ICD lead artifact on CMR where endocardial followed by epicardial access had to be undertaken. Thus, access for the ablation was directed by CMR in 95% of the patients. VT was inducible in all patients; procedure duration averaged 8 hours with fluoroscopy and ablation times each averaging an hour and 15 minutes. Acute procedural success (defined as noninducibility of VT postablation) was seen in 75% of these patients. Survival free of VT was 80% over 17 months