MADIT-CRT: LBBB risk-stratifies mild-HF patients

March 04, 2011

Dallas, TX - Left bundle-branch block (LBBB) on the electrocardiogram identifies a subset of patients with NYHA class 1-2 heart failure and a wide QRS complex who gain the most from cardiac resynchronization therapy (CRT), according to a subanalysis of MADIT-CRT[1].

The finding, now published online February 28, 2011 in Circulation, was considered by the FDA Circulatory System Devices Advisory Panel and figured prominently in its recommendation last year to expand CRT indications to include patients with mild heart failure, based on MADIT-CRT. The agency followed the panel's lead and updated the indications to include patients with NYHA class 1-2 heart failure, LBBB, an LVEF <30%, and a QRS duration >130 ms, as reported by heartwire. Previously, the CRT indication had been limited to NYHA class 3-4 patients with an LVEF <35% and a QRS >120 ms.

The trial had randomized 1820 patients with systolic NYHA class 1-2 heart failure and a wide QRS to receive a defibrillator with or without CRT capability. As previously reported in detail by heart wire , patients receiving CRT showed a one-third fall in risk of death or heart-failure events, the primary end point, over 2.5 years; the end point's latter component accounted for most of the benefit.

In the new MADIT-CRT report, from authors led by Dr Wojciech Zareba (University of Rochester, NY), 70% of the trial's 1817 patients with evaluable baseline ECGs showed an LBBB pattern, while 13% and 17%, respectively, showed right bundle-branch block or nonspecific intraventricular conduction disturbances.

The adjusted hazard ratio (HR) for the primary end point in the trial's LBBB subset who received CRT vs no CRT was 0.47 (95% CI 0.37-0.61), while the corresponding HR for the non-LBBB subset was 1.24 (95% CI 0.85-1.81); the interaction between LBBB and non-LBBB groups for the primary end point was significant at p<0.001. As in the overall trial, the benefit in LBBB patients was driven by a reduction in rate of heart-failure events.

LBBB patients also showed significantly greater reverse remodeling effects of CRT at echocardiography, as measured by changes in LV end-systolic and end-diastolic volumes (p<0.001 for both parameters).

As a condition of the expanded CRT indication, Boston Scientific agreed to conduct a postapproval analysis of the long-term survival and safety outcomes of CRT therapy in patients with LBBB, heart wire previously noted.

MADIT-CRT was supported by a research grant from Boston Scientific; disclosures for the coauthors are listed in the paper .

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