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Heart Rhythm. 2009 Oct;6(10):1439-47. doi: 10.1016/j.hrthm.2009.07.009. Epub 2009 Jul 10.

Upgrade and de novo cardiac resynchronization therapy: impact of paced or intrinsic QRS morphology on outcomes and survival.

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Mayo Clinic, Rochester, MN 55905, USA.



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.


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


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.


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).


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.

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