Elsevier

Heart Rhythm

Volume 6, Issue 10, October 2009, Pages 1439-1447
Heart Rhythm

Clinical
Device
Upgrade and de novo cardiac resynchronization therapy: Impact of paced or intrinsic QRS morphology on outcomes and survival

https://doi.org/10.1016/j.hrthm.2009.07.009Get rights and content

Background

Cardiac resynchronization therapy (CRT) improves outcomes in patients with left bundle branch block (LBBB), but the benefits of CRT in patients with other QRS morphologies or previous pacing are uncertain.

Objective

The purpose of this study was to describe outcomes in patients with prior right ventricular pacing and non-LBBB morphologies.

Methods

We studied 505 patients who underwent de novo CRT (n = 338) or CRT upgrade (n = 167). De novo patients were categorized by underlying QRS morphology: LBBB (67%), right bundle branch block (RBBB; 11%), intraventricular conduction delay (IVCD; 13%), and QRS <120 ms (9%). Upgrade patients were categorized by the percentage of previous ventricular pacing.

Results

Patients were followed for death over a median of 2.6 years (interquartile range 1.6–4.0). New York Heart Association (NYHA) functional class and echocardiographic improvements were similar in de novo and upgrade patients. However, within the de novo group, NYHA improvements were less in patients with RBBB (0.3 ± 0.8; P = .014) or IVCD (0.2 ± 0.7; P = .001) than in those with LBBB (0.7 ± 0.8). These patients had less left ventricular functional improvement as well. Survival was comparable after de novo versus upgrade CRT (61% vs 63% at 4 years; P = .906). No clinical or survival differences were noted in upgrade patients based on the percentage of previous pacing. However, survival in de novo CRT recipients with RBBB (32%) was lower than in those with LBBB (66%; P <.001), and RBBB independently predicted death (hazard ratio 3.5, confidence interval 1.9–6.5; P <.001).

Conclusion

RBBB and IVCD result in less clinical improvement or worsened survival after CRT. Additional selection criteria may be beneficial in identifying potential responders with RBBB, IVCD, or narrow QRS.

Introduction

Cardiac resynchronization therapy (CRT) has been shown to improve outcomes in trials in which most patients with drug-refractory heart failure (HF) had intrinsic left bundle branch block (LBBB).1, 2, 3, 4 However, the benefits of CRT have not been conclusively demonstrated in patients with other native QRS morphologies or those who have undergone right ventricular (RV) pacing in the setting of a preexisting pacemaker or defibrillator due to limited representation within randomized controlled trials and variable outcomes.

The impact of QRS morphology on HF outcomes has been examined in four randomized trials of CRT.1, 2, 4, 5 In a substudy of CRT-D recipients from the MIRACLE (Multicenter InSync Randomized Clinical Evaluation) ICD study, RBBB was associated with less improvement in peak oxygen consumption than other QRS morphologies in univariate, but not multivariate, analysis.6 In a retrospective, pooled analysis from MIRACLE and CONTAK-CD that compared outcomes in 34 patients with RBBB who received CRT and 27 who received medical management, New York Heart Association (NYHA) functional class was the only clinical outcome that improved significantly more after active CRT. Improvements in other HF parameters, such as 6-minute walk, peak oxygen consumption, and ejection fraction, did not differ significantly between the groups.7 In the Comparison of Medical Therapy, Pacing and Defibrillation in Heart Failure (COMPANION) trial, a survival benefit of CRT over pharmacologic therapy was observed in patients with LBBB but not in those with other QRS morphologies.4 Together, these data raise the concern that patients with non-LBBB morphologies somehow fare worse than their LBBB counterparts after CRT, possibly contributing to a significant nonresponse rate. The few retrospective studies that have attempted to clarify the prognostic impact of QRS morphology on survival after CRT have yielded mixed results.8, 9

In a subset of potential CRT recipients who have previously undergone pacemaker or defibrillator placement, the underlying QRS morphology is a paced LBBB. In such patients, particularly those with AV nodal disease, chronic RV pacing can result in interventricular and intraventricular dyssynchrony in the short term and in adverse biventricular remodeling that predisposes to HF or atrial fibrillation in the long term.10, 11, 12, 13 Although upgrade to CRT has been recommended as a class IIa indication in these patients who otherwise meet CRT criteria, this recommendation is based largely on consensus and only on limited clinical data.14, 15

The aim of this single-center, retrospective study was to assess the impact of native QRS morphologies or previous RV pacing on clinical and survival outcomes of de novo or upgrade CRT recipients.

Section snippets

Study design

This cohort consists of 505 consecutive patients who underwent de novo (n = 338; 39 CRT and 299 CRT-D) or upgrade CRT (n = 167; 10 CRT and 157 CRT-D) at Mayo Clinic from January 1, 2002, to December 31, 2006. Indications for CRT were HF symptoms despite optimal medical therapy (NYHA class II or greater), left ventricular ejection fraction (LVEF) ≤35%, and QRS duration ≥120 ms with the exception of select patients with QRS <120 ms. Patients with QRS <120 ms were included based on the combined

Patient characteristics

Baseline characteristics in the de novo (n = 338) and upgrade groups (n = 167) are summarized in Table 1. The de novo group was younger, had less chronic atrial fibrillation, had less prolonged QRS duration, and had lower creatinine levels than the upgrade group. NYHA class, echocardiographic parameters, and pharmacologic HF regimens were similar (>80% on beta blockers, >60% digoxin), except for the more frequent use of angiotensin-converting enzyme inhibitor or angiotensin receptor blocker in

Discussion

There were two main findings in this study of CRT in a clinical practice population. First, no evidence of a difference in outcomes between the upgrade and de novo implantation groups was observed. Second, native QRS morphology had clinical and prognostic value in recipients of de novo CRT. Patients with RBBB or nonspecific IVCD experienced less clinical improvement and less LV functional improvement. In addition, patients with RBBB experienced less survival benefit than did those with

Conclusion

Despite these limitations, our data identify the relative prognostic values of device upgrade and intrinsic QRS morphology in CRT in a clinical practice population. We established that CRT upgrade is comparable to, but not better than, de novo implantation in clinical and survival outcomes. We further identified less clinical and/or survival benefit for patients with RBBB and IVCD. Patients with widened QRS without LBBB appear less likely to respond to CRT and, therefore, may be better served

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    Dr. Wokhlu has received travel support from Medtronic, Boston Scientific, and St. Jude Medical to attend educational seminars. Dr. Hayes is an educational speaker and serves on the advisory boards for Medtronic, Boston Scientific, Sorin Medical Group, and St. Jude Medical, and he is a member of the steering committee for St. Jude Medical. Dr. Asirvatham receives honoraria and is on the speaker's board for St. Jude Medical, Boston Scientific, and Medtronic. In addition, he is a co-patent holder for an alternative resynchronization therapy technique. Ms. Webster is on an advisory board for Boston Scientific.

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