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.