Abstract 19010: Exercise but Not Pacing Affects Coronary-Cardiac Interaction via Reflected Waves From the Aorta

Background: Not only the interaction with cardiac mechanics, but also the systemic circulation determines coronary hemodynamic waveforms. Coronary wave intensity can distinguish between forward (FW) waves entering from the aorta and backward (BW) waves originating from the microcirculation. The aim of this study was to assess contributions of the systemic circulation to cardiac-coronary interaction by comparing exercise, having a profound influence on the systemic circulation, with right atrial pacing where the systemic circulation is minimally affected. Methods: During cardiac catheterization we recorded aortic pressure (Pa), distal coronary pressure (Pd) and flow velocity (U) in diseased coronary arteries. In 10 subjects heart rate (HR) was increased by right atrial pacing at 120 bpm. 11 other patients exercised using a supine cycle ergometer at increasing workload. Net wave intensity was computed as dI= (dPd/dt)(dU/dt) and the energy of the FW and BW waves was derived by the areas under the curve. Results: Resting values of systemic and coronary hemodynamic were similar in both groups, with HR = 73 ±4 bpm, Pa = 104 ±5 mmHg, Pd = 85 ±10 mmHg and U = 16.2 ±2.1 cm/s. Exercise increased HR to 108 ±7 bpm which did not differ from that during pacing. Pa and Pd increased with exercise by 20 mmHg and 8 mmHg, resp. (p<0.05), whilst pacing raised Pa by only 5 mmHg (p<0.05) at unchanged Pd. U similarly increased to 23.1±3.0 cm/s by pacing and exercise. Coronary wave energy at rest was the same for both groups. The BW compression wave more than doubled with both pacing and exercise, while the early FW compression wave was unchanged by exercise and much reduced by pacing from 1.9 ± 0.6 to 0.3±0.1 Jm -2 s -2 (p<0.05). The FW expansion wave at the onset of relaxation increased from 1.6±0.5 to 3.5±1.0 Jm -2 s -2 (p<0.05) with exercise but was not altered by pacing. The BW expansion wave that drives diastolic coronary flow more than doubled with exercise, but only increased by 63% with pacing. Conclusion: Exercise more profoundly affects cardiac-coronary interaction than pacing and improves the energy of FW and BW waves during cardiac relaxation. This is likely due to increased contractility, assisted by added reflection from the systemic circulation that enters the coronary arteries via the aorta.