Impact of Simulated Vascular Aging and Heart Rate on Myocardial Efficiency: A Tale of Two Paradigms from In Silico Modelling

INTRODUCTION: Vascular aging is associated with a loss of aortic compliance (CA), which results in increased left ventricular pressure-volume area (PVA), stroke work (SW) and myocardial oxygen consumption (MVO₂). Myocardial efficiency (MyoEff) is derived from the PVA and MVO₂ construct, which includes potential energy (PE). However, the SW/MVO₂ ratio does not include PE and provides a more accurate physiologic measure. METHODS: We used a modified computational model (CM) to assess PVA and SW and calculate MVO₂ using a pressure-work index (e MVO₂), to derive MyoEff-PVA and MyoEff-SW metrics. Phase I evaluated five levels of human CA from normal (N) to stiff (S) at 80 bpm, and Phase II evaluated two levels of CA (N and S) at three heart rates (60, 100, and 140 bpm). RESULTS: During Phase I, MyoEff-PVA increased from 20.7 to 31.2%, and MyoEff-SW increased from 14.8 to 18.9%. In Phase II, during the N setting coupled with increases in the heart rate, the MyoEff-PVA decreased from 29.4 to 14.8 to 9.5%; the MyoEff-SW also decreased from 22.5 to 10.3 to 5.9%. As expected, during the S setting, MyoEff-PVA decreased from 45.5 to 22.9 to 14.8; a similar effect occurred with the MyoEff-SW, demonstrating a decrease from 29.9 to 13.9 to 7.9%, respectively. CONCLUSIONS: The CM provided insights into a simple and clinically relevant calculation for assessing MyoEff. The agreement on the CM metrics aligns with studies conducted previously in the clinical setting.