Detection and hemodynamic significance of cardiac pacemaker-induced phrenic nerve stimulation

The authors investigated acoustic cardiography, the digital analysis of electrocardiogram (ECG) and heart sounds, to detect phrenic nerve stimulation (PNS) and assess its hemodynamic significance. They studied 42 patients and induced 46 instances of PNS induced through cardiac pacing at various locations in the heart. These 46 instances of PNS were either independently documented using fluoroscopy or were symptomatic. The authors collected acoustic cardiography data including the electromechanical activation time (interval from Q onset to the first heart sound [S1]) as a percentage of the RR interval (%EMAT) to assess systolic function. Acoustic cardiography provided evidence of PNS when it occurred. They also found significant %EMAT prolongation when right ventricular pacing was associated with PNS (Delta%EMAT=2.7, P=.012), but none beyond the normal range with right ventricular pacing in the absence of PNS. Documented PNS occurred in 33 episodes (60%) in patients with noticeable symptoms. Stimulation amplitudes could be found that generated asymptomatic PNS for all of the five participants explicitly tested for it. PNS can be asymptomatic. PNS due to right ventricular pacing is associated with impaired left ventricular systolic function. Acoustic cardiography is an effective method of detecting and assessing the hemodynamic significance of pacemaker-related PNS.