ABSTRACT
BACKGROUND: In patients with narrow QRS complex, both ventricular and biventricular pacing is associated with increased cardiac morbidity and mortality. This risk is not decreased by ventricular pacing avoidance algorithms which cause non-physiologic atrioventricular delays. OBJECTIVE: To report outcomes in patients with narrow QRS complex, when paced complex is in normal range and physiologic atrioventricular delays are programmed. METHODS: In 196 patients with QRS duration of 92 ± 10 msec, permanent pacing was done at site of His bundle electrogram. The pacemakers were then programmed to maintain physiologic AV delays and increase heart rates in response to exercise. Patients received usual care and were followed for 3-years. RESULTS: The paced complex exhibited a delta wave and the ventricular activation time, QRS axis and lead-I voltage remained in normal range. Physiologic programming resulted in His bundle pacing burden of 92%. In patients with decreased ejection fraction, there was significant improvement in left ventricular function, left ventricular dilatation and mitral regurgitation (p <0.003). In patients with normal ejection fraction, left ventricular function remained normal without new valvular abnormalities. The 3-year all-cause mortality was 10%, and there was no increase in heart failure admissions. CONCLUSION: In patients with narrow QRS complex, when paced QRS morphology is maintained in normal range and atrio-ventricular dyssynchrony is avoided, His bundle pacing is associated with a low all-cause mortality and improvement in abnormal echocardiographic parameters. The paced QRS morphology and physiologic atrioventricular delays may be important factors to evaluate in future trials of conduction system pacing.
