Abstract 1133: Parasympathetic Effect On Cardiac Electrophysiology Is Preserved At Rest In Patients With Depressed Left Ventricular Ejection Fraction
Introduction: Parasympathetic effects (PE) on cardiac electrophysiology during exercise (Ex) and post-exercise recovery (Rec), a time of heightened risk for sudden death, have not been studied in patients with depressed left ventricular ejection fraction (LVEF). We hypothesized that PE are suppressed in subjects with low LVEF.
Methods: Non-invasive programmed stimulation (NIPS) was performed during multiple bicycle exercise sessions in 10 subjects (9 men, age 60 ± 9 yr, LVEF 29 ± 8%) with ICDs during rest, Ex, and Rec at baseline and after parasympathetic blockade with atropine. PE was calculated as the difference in the value of the parameter of interest in the absence of atropine minus its value in the presence of atropine.
Results: PE (figure⇓; *p<0.05) was 34 ± 10% on sinus cycle length, 27 ± 14% on AV block cycle length, 19 ± 5% on AV interval, and 6.2 ± 4.5% on ventricular effective refractory period (VERP) at rest. PE on VERP was 15.8 ± 11.3 ms (p=0.02) at rest, 4.7 ± 15.2 ms (p=0.4) during Ex, and 6.8 ± 15.5 ms (p=0.2) during Rec. There was no significant difference between PE on any of the electrophysiologic parameters in this group and a group of previously reported patients with normal LVEF. VERPs were longer in the low LVEF group in all stages (p=0.008).
Conclusions: Surprisingly, PE is preserved in patients with depressed LVEF, though there may be a longer lag to restoration of PE in the recovery period. These data underscore that understanding the pathophysiologic role of PE in sudden death cannot be achieved with surrogate measures of sinus node effects.