Interlead electrical delays and scar tissue: Response to cardiac resynchronization therapy in patients with ischemic cardiomyopathy

BACKGROUND: The importance of interlead electrical delays (IEDs) in the presence of scar tissue for response to cardiac resynchronization therapy (CRT) in patients with ischemic cardiomyopathy is poorly described.

METHODS: Sixty-eight CRT patients with ischemic cardiomyopathy and left bundle branch block were included. IEDs, the time between sensing of native impulse at the RV lead and LV lead, were measured at implantation and after 8 months. Magnetic resonance imaging was used for assessment of scar tissue. Echocardiographic response was defined as ≥ 15% decrease in left ventricular end-systolic volume. New York Heart Association (NYHA) class, Minnesota Living with Heart Failure Questionnaire, and 6-minute walk-test were used to assess clinical response.

RESULTS: A total of 44 patients (65 %) were responders to CRT. At implantation, IEDs were significantly longer among responders compared to nonresponders (RV-LV-IED: 87 ms ± 33 ms vs 65 ms ± 47 ms, P < 0.05), most evident in patients with QRS < 150 ms. Responders had less myocardial scar tissue than nonresponders (1 ± 0.5 vs 1.4 ± 0.6, P = 0.01). However, in the multivariate model including QRS duration and scar tissue, IEDs were independently associated with LV remodeling after CRT: odds ratio 3.99 [95% confidence interval 1.02-15.7] (P = 0.04). During the course of treatment, no changes were observed in IEDs among echocardiographic responders.

CONCLUSION: RV-LV-IED was an independent marker of response in CRT patients with ischemic cardiomyopathy even in the presence of scar tissue and may be particularly useful in patients with QRS < 150 ms. CRT did not influence this measurement over time.