Beneficial effects of high output His bundle pacing in patients with heart failure, narrow QRS

Abstract Funding Acknowledgements Type of funding sources: None. Background Cardiac Resynchronization Therapy (CRT) decreases heart failure (HF) hospitalizations and mortality and increases left ventricular Ejection Fraction (EF) in patients with dilated cardiomyopathy, left bundle branch block and QRS>130msec1. However, CRT is not beneficial in HF patients with narrow QRS3. Purpose We performed His Bundle Pacing (HBP) with high output (3.5V/1msec) in HF patients with dilated or ischemic cardiomyopathy and narrow QRS to prove hemodynamic benefit independently of the QRS duration or AV delay shortening. Methods 9 male patients with dilated cardiomyopathy (EF<35%) and narrow QRS (<110ms) were referred for implantation of a defibrillator. We implanted an ICD- HBP system, and we collected clinical, echocardiographic, and electrocardiographic data. Results We obtained HBP in all 9 patients successfully. Basal mean EF was 31±4% and increased to 43±6% (P<0.001) after a median follow-up of 116 days. Left ventricular end-diastolic diameter and left ventricular end-diastolic volume decreased from 62±5 to 59±6ml (P=0.014) and from 188±87 to 144±35ml (P=0.095), respectively. Left ventricular end-systolic volume decreased from 139±78 to 85±29 (P=0.035). NYHA class decreased by one class in every patient after only one month. Baseline QRS duration remained stable after pacing from 107±7 to 118±15ms. In one patient an iatrogenic right bundle branch block was created which was corrected partially by His bundle pacing. PQ after implantation was shorter (from 167±23 to 121±14 (P=0.030) so as to pace the ventricle. HBP threshold was 1.24V±0.50/1msec, the impedance was 529±116 Ohms while R-wave was 3.8±1.7mV. In one out of 9 patients, threshold increased from 1 to 2V/1msec in 6months and then remained stable. In the other eight patients, threshold remained stable. Conclusions HBP in HF patients with dilated cardiomyopathy and narrow QRS improves hemodynamic function and decreases NYHA class. This benefit appears to be produced by a higher stimulation output. We cannot exclude that a very short AV delay could be favorable. To our knowledge these are the first cases of beneficial HBP in HF patients with narrow QRS. There is urgent need for large, randomized clinical trials.