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CLINICAL RESEARCH: HEART RHYTHM DISORDER

Pacing-Induced Increase in QT Dispersion Predicts Sudden Cardiac Death Following Cardiac Resynchronization Therapy

Department of Cardiology, Good Hope Hospital, Sutton Coldfield, United Kingdom.

Manuscript received July 4, 2005; revised manuscript received September 7, 2005, accepted December 1, 2005.

^_* Reprint requests and correspondence: Dr. Francisco Leyva, Department of Cardiology, Good Hope Hospital, Rectory Road, Sutton Coldfield, West Midlands B75 7RR, United Kingdom. (Email: francisco.leyva{at}goodhope.nhs.uk).

OBJECTIVES: This study was designed to determine whether cardiac resynchronization therapy (CRT) by means of biventricular pacing (BiVP) alters the QT interval (QT_c) and QT dispersion (QTD), and whether such changes relate to the risk of developing major arrhythmic events (MAE).

BACKGROUND: Prolonged QT_c is associated with MAE. Left ventricular pacing and BiVP alter QT_c.

METHODS: A total of 75 patients with drug-resistant heart failure (New York Heart Association functional class III/IV) and QRS duration 120 ms underwent CRT. The QT_c and QTD were measured before and 48 days after BiVP.

RESULTS: Over 807 days (range 93 to 1,543 days), 11 patients had a MAE. Compared to baseline, at 48 days after CRT, QTD increased in 47% of patients and QT_c decreased in 53%. The QT_c at follow-up was higher in MAE patients compared with no-MAE patients (35.9 ± 14.2 ms vs. 0.52 ± 6.0 ms; p = 0.0323). Similar differential responses for QTD were observed (46.4 ± 13.5 ms in MAE vs. –5.1 ± 4.1 ms in no MAE, p < 0.0001). The MAE occurred in 29% of patients exhibiting an increase in QTD and in 3% of those exhibiting a decrease (p = 0.0017). In multiple regression analyses, change in QTD from baseline (QTD) strongly predicted MAE, independent of QT_c, QRS duration, and left ventricular ejection fraction and end-diastolic volume (p < 0.001). Differences in survival curves were observed when patients were dichotomized according to whether QTD increased or decreased in relation to baseline values (p < 0.0001).

CONCLUSIONS: The MAE in patients with BiVP are related to pacing-induced increases in QTD. Measures of ventricular repolarization at the time of pacemaker implantation may guide selection of patients for combined CRT and defibrillator therapy.

Abbreviations and Acronyms   BiVP = biventricular pacing   CARE-HF = Cardiac Resynchronization Heart Failure study   CRT = cardiac resynchronization therapy   HF = heart failure   ICD = implantable cardioverter-defibrillator   LV = left ventricle/ventricular   LVEDV = left ventricular end-diastolic volume   LVEF = left ventricular ejection fraction   LVESV = left ventricular end-systolic volume   MAE = major arrhythmic events   NYHA = New York Heart Association   QTc = rate-corrected QT interval   QTD = QT dispersion   RV = right ventricle/ventricular

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