Left ventricular dimensions predict risk of appropriate shocks but not mortality in cardiac resynchronization therapy-defibrillator recipients with left bundle-branch block and non-ischemic cardiomyopathy.

AIMS: Patients with non-ischaemic cardiomyopathy (NICM) and left bundle-branch block (LBBB) often benefit markedly from cardiac resynchronization therapy (CRT). Cardiac resynchronization therapy responders have a lower risk of appropriate device shocks from CRT-defibrillators (CRT-D) than do non-responders. Larger baseline left ventricular (LV) dimensions may be associated with less CRT response and thus greater risk of appropriate shocks.

METHODS AND RESULTS: We analysed all (n = 249; 55% female) primary prevention CRT-D recipients at our institution with LBBB, NICM, and measured LV dimensions prior to device implant for the outcomes of (i) appropriate shocks, (ii) any appropriate tachyarrhythmia therapies, and (iii) risk of death, transplant, or left ventricular assist device (LVAD). During 59 months (interquartile range 21.5-91.5) follow-up, 19 (8%) patients received ≥1 appropriate shock, and 67 (27%) patients died, received a transplant, or required LVAD. Receiver-operating characteristic analysis of LV end-diastolic diameter (LVEDD) per meter height vs. appropriate shock(s) revealed an area under the curve of 0.75 (95% CI 0.65-0.85; P < 0.001). No patient with indexed LVEDD <3.36 cm/m (n = 76) received a shock. There was no statistically significant difference in risk of death, transplant, or LVAD (corrected HR 1.67, 95% CI 0.90-3.03; P = 0.103) in patients with indexed LVEDD above this cut-off compared to those with smaller dimension. Among 102 patients with paired quantitative echocardiograms, there was no difference in LVEF change between patients with indexed LVEDD <3.36 cm/m (n = 27; median 11%) and larger (n = 75; median 14%).

CONCLUSION: Patients with LVEDD <3.36 cm/m height prior to CRT-D implant in the setting of NICM and LBBB have minimal risk of appropriate shocks but similar risk of death, transplant- and LVAD and similar extent of LV functional improvement as patients with larger LVEDD. CRT-pacemakers may be appropriate in such patients.