Influence of the preimplantation QRS axis on responses to cardiac resynchronization therapy.

INTRODUCTION AND OBJECTIVES The aim of this study was to determine whether measurement of the QRS axis can help to predict outcome in patients undergoing cardiac resynchronization therapy. METHODS The study included 78 patients who had undergone successful cardiac resynchronization device implantation. Patients were classified as having either a normal QRS axis (i.e., between -30 degrees and +120 degrees) or a left QRS axis deviation (i.e., between -30 degrees and -90 degrees). Patients were regarded as responders if they fulfilled all of the following criteria: their functional class improved by at least one grade, their left ventricular ejection fraction increased by at least 5%, they did not need hospitalization for worsening heart failure, and they were still alive at 12-month follow-up. RESULTS After adjustment for age, preimplantation left ventricular ejection fraction, etiology and mitral regurgitation, a statistically significant interaction was found between the QRS axis and lead location (P=.026). There was a better response with an anterior lead location if the patient had a left QRS axis deviation. CONCLUSIONS A significant interaction was found between the lead location and the preimplantation QRS electrical axis, such that there was a better response to resynchronization therapy when the lead was implanted in the anterior interventricular vein if the patient had a left QRS axis deviation.