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Background— An implantable cardioverter-defibrillator (ICD) is the therapy of choice for primary prevention in patients with ischemia who are at risk for sudden cardiac death (SCD). One third of patients with significant coronary disease have chronic total coronary occlusion (CTO), which is associated with long-term mortality in patients with previous myocardial infarction. However, the impact of CTO on the occurrence of ventricular arrhythmias and long-term mortality in ICD recipients remains unknown. Methods and Results— All consecutive patients with coronary artery disease receiving ICD therapy for the prevention of SCD were included in the study. Among other characteristics, the existence of CTO was assessed. During follow-up, the occurrence of appropriate device delivery because of ventricular arrhythmias as well as mortality were noted. A total of 162 patients (mean age, 62±9 years; 93% men) with an ICD were included and followed for a median of 26 months (interquartile range, 12–42). At least 1 CTO was present in 71 (44%) patients. Appropriate device therapy was detected in 18% of the patients during the follow-up. The presence of CTO was associated with higher ventricular arrhythmia and mortality rates (log-rank test, P =0.003). Conclusions— In patients with ischemic heart disease receiving ICDs for primary prevention of SCD, CTO is an independent predictor for the occurrence of ventricular arrhythmias and has an adverse impact on long-term mortality.

Background —Different responses to entrainment have been reported in relation to the pacing site of a variety of tachycardias. However, transient entrainment of bundle-branch reentrant tachycardia (BBRT) has not been investigated systematically. Methods and Results —We attempted entrainment of 13 BBRTs in 9 patients by pacing first the right ventricle and then the right atrium. The initial pacing cycle length (CL) was 10 ms faster than the tachycardia CL. Subsequent pacing sequences were performed with 5- to 10-ms CL decrements until tachycardia termination or loss of postatropine 1:1 AV conduction. Both full ventricular-paced and AV-conducted QRS complex references were obtained during sinus rhythm pacing from the same sites and with similar CL as during entrainment. Transient entrainment was achieved by ventricular and atrial stimulation in 11 and 8 tachycardias, respectively. Constant fusion was always present during entrainment by ventricular stimulation. There was no change in the QRS complex (orthodromically concealed fusion) during entrainment by atrial stimulation in 6 of 6 tachycardias with left bundle-branch block morphology and in 1 of 2 tachycardias with right bundle-branch block morphology. Conclusions —BBRT, especially if it has a left bundle-branch block morphology, can be differentiated from other wide-QRS-complex tachycardia mechanisms through analysis of the ECGs recorded during tachycardia entrainment by atrial and ventricular stimulation. This diagnostic approach may be especially useful when it is difficult to record a stable or sufficiently sized His bundle electrogram or when spontaneous changes in the ventricular CL precede similar changes in the His bundle CL.

We appreciate the authors' careful review of our manuscript and prepared the following response to their comments. The first comment is that the SmartDelay Determined AV Optimization: A Comparison to Other AV Delay Methods Used in Cardiac Resynchronization Therapy (SMART-AV) trial was underpowered to detect the additional response to atrioventricular (AV) optimization. Importantly, the authors performed a post hoc power calculation, basing their calculations on the observed fixed-group response. These calculations do not have the same validity as prospective power calculations and must be interpreted with great caution.1 Second, the noninferiority margin of 15 mL for a left ventricular end-systolic volume difference from baseline to 6 months post–cardiac resynchronization therapy was …