Published Online
on June 11, 2009

A more recent version of this article appeared on August 1, 2009

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Original Article

Phrenic Stimulation: A Challenge for Cardiac Resynchronization Therapy

Mauro Biffi¹; Carlotta Moschini; Matteo Bertini; Davide Saporito; Matteo Ziacchi; Igor Diemberger; Cinzia Valzania; Giulia Domenichini; Elena Cervi; Cristian Martignani; Diego Sangiorgi; Angelo Branzi and Giuseppe Boriani

University of Bologna, Bologna, Italy

¹ E-mail: mziacchi{at}libero.it

Background—Phrenic stimulation (PS) may hinder left ventricular (LV) pacing. We prospectively observed its prevalence in consecutive CRT patients.

Methods and Results—In the years 2003–2006, 197 patients received a CRT device. PS and LV threshold measurements were carried out either at implantation and at 6–months follow–up. LV reverse remodeling was assessed by echocardiography before implantation and at follow-up. LV lead placement was lateral/posterolateral in 86% of patients. Both PS and LV reverse remodeling occurred most frequently at the lateral/posterolateral LV pacing sites (p<0.001). PS was detected in 73 (37%) of patients, and was clinically relevant in 41 (22%). The detection of PS at implantation had a poor sensitivity, as it occurred only in left lateral or sitting position in 27 patients. 10 patients (5%) underwent repeated surgery, and 4 (2%) had CRT turned off, because of PS. At follow-up, we could manage PS non-invasively in 32 patients with a small PS–LV threshold difference: in 20 by cathode programmability (3 also thanks to automatic management of LV output), and in 12 (without cathode programmability) by programming the LV output as threshold+1V.

Conclusions—PS may seriously hinder CRT. A bipolar LV lead and cathode programmability are mandatory to avoid PS by changing the LV pacing vector at target sites for CRT. LV stability at target sites despite PS should also be pursued by these means. The automatic adjustment of LV pacing output is complimentary in patients with a small PS–LV threshold difference.

Key Words: heart failure • cardiac resynchronization therapy • device technology • phrenic stimulation • reverse remodeling