Effect of QRS Morphology on Clinical Event Reduction With Cardiac Resynchronization Therapy: Meta-Analysis of Randomized Controlled Trials

Harrington-McLaughlin Heart and Vascular Institute, University Hospitals Case Medical Center, Cleveland, OH, USA.
American heart journal (Impact Factor: 4.46). 02/2012; 163(2):260-7.e3. DOI: 10.1016/j.ahj.2011.11.014
Source: PubMed


Cardiac resynchronization therapy (CRT) is effective in reducing clinical events in systolic heart failure patients with a wide QRS. Previous retrospective studies suggest only patients with QRS prolongation due to a left bundle-branch block (LBBB) benefit from CRT. Our objective was to examine this by performing a meta-analysis of all randomized controlled trials of CRT.
Systematic searches of MEDLINE and the Food and Drug Administration official website were conducted for randomized controlled CRT trials. Trials reporting adverse clinical events (eg, all-cause mortality, heart failure hospitalizations) according to QRS morphology were included in the meta-analysis.
Four randomized trials totaling 5,356 patients met the inclusion criteria. In patients with LBBB at baseline, there was a highly significant reduction in composite adverse clinical events with CRT (RR = 0.64 [95% CI (0.52-0.77)], P = .00001). However no such benefit was observed for patients with non-LBBB conduction abnormalities (RR = 0.97 [95% CI (0.82-1.15)], P = .75). When examined separately, there was no benefit in patients with right-bundle branch block (RR = 0.91 [95% CI (0.69-1.20)], P = .49) or non-specific intraventricular conduction delay (RR = 1.19 [95% CI (0.87-1.63)], P = .28). There was no heterogeneity among the clinical trials with regards to the lack of benefit in non-LBBB patients (I(2) = 0%). When directly compared, the difference in effect of CRT between LBBB versus non-LBBB patients was highly statistically significant (P = .0001 by heterogeneity analysis).
While CRT was very effective in reducing clinical events in patients with LBBB, it did not reduce such events in patients with wide QRS due to other conduction abnormalities.

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    • "Recently, left bundle branch block (LBBB) morphology and QRS width, etiology, mechanical activation delay and electrical separation of the implanted right ventricular (RV) and LV leads have been identified as predictors of favorable outcome [4] [5] [6] [7] [8] [9]. The substrate for CRT is to resolve a significant electrical activation delay in the LV. "
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    ABSTRACT: Pacing lead electrical delays and strict left bundle branch block (LBBB) criteria were assessed against cardiac resynchronization therapy (CRT) outcome. Forty-nine patients with LBBB and QRS duration >130 milliseconds underwent CRT-implantation. Sensed right ventricular to left ventricular electrical delay (RV-LV-IED) was measured. Response to CRT was defined as ≥15% decrease in left ventricular end-systolic volume. Eighteen of 20 (90%) patients with non-ischemic dilated cardiomyopathy (DCM) and 18 of 29 (62%) with ischemic heart disease (IHD) responded to CRT, p<0.01. When applying new strict ECG criteria subsequent rates of response in DCM were 18/19 (95%) and in IHD of 18/23 (78%) respectively, p<0.05 between IHD groups. Correspondingly, RV-LV-IED was longer in DCM compared to IHD patients and in responders compared to non-responders, p=0.017 and p<0.001, respectively. Interventricular electrical delay predicts left ventricular remodeling after CRT and new, strict ECG criteria of LBBB are superior in predicting remodeling. Copyright © 2015. Published by Elsevier Inc.
    No preview · Article · Jul 2015 · Journal of electrocardiology
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    • "A meta-analysis was performed to evaluate the effect of CRT on clinical events with regards to different types of baseline conduction abnormalities using data from randomized controlled trials. Four randomized trials totaling 5,356 patients met the inclusion criteria and they concluded that while CRT was very effective in reducing clinical events in patients with LBBB, it did not reduce such events in patients with wide QRS due to other conduction abnormalities.15 In the Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) trial, patients without LBBB did not have a statistically significant benefit, and those with QRS duration ≤147 ms had absolutely no benefit.16 "
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    ABSTRACT: The QRS represents the simultaneous activation of the right and left ventricles, although most of the QRS waveform is derived from the larger left ventricular musculature. Although normal QRS duration is <100 millisecond (ms), its duration and shape are quite variable from patient to patient in idiopathic dilated cardiomyopathy (IDCM). Prolongation of QRS occurs in 14% to 47% of heart failure (HF) patients. Left bundle branch block (LBBB) is far more common than right bundle branch block (RBBB). Dyssynchronous left ventricular activation due to LBBB and other intraventricular conduction blocks provides the rationale for the use of cardiac resynchronization therapy with biventricular pacing in patients with IDCM. Fragmented QRS (fQRS) is a marker of depolarization abnormality and present in significant number of the patients with IDCM and narrow QRS complexes. It is associated with arrhythmic events and intraventricular dyssynchrony. The purpose of this manuscript is to present an overview on some clinical, echocardiographic and prognostic implications of various QRS morphologies in patients with IDCM.
    Full-text · Article · Jun 2014
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    • "Patients with a prolonged QRS duration may have a left bundle-branch block (LBBB), right bundle-branch Block (RBBB), nonspecific intraventricular conduction delay (IVCD), or paced rhythm. The presence of typical LBBB morphology is a strong predictor of response compared with right bundle branch block (RBBB) morphology and non-specific intraventricular conduction delay (IVCD) that has a much lower probability of CRT response [39, 40]. "
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    ABSTRACT: Heart failure affects millions of patients all over the world, and its treatment is a major clinical challenge. Cardiac dyssynchrony is common among patients with advanced heart failure. Resynchronization therapy is a major advancement in heart failure management, but unfortunately not all patients respond to this therapy. Hence, many diagnostic tests have been used to predict the response and prognosis after cardiac resynchronization therapy. In this paper we summarize the usefulness of different diagnostic modalities with special emphasis on the role of surface electrocardiogram as a major predictor of response to cardiac resynchronization therapy.
    Full-text · Article · Mar 2013 · The Scientific World Journal
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