Simulation of Exercise-Induced Syncope in a Heart Model with Severe Aortic Valve Stenosis

Abstract

Severe aortic valve stenosis (AVS) can cause an exercise-induced reflex syncope (RS). The precise mechanism of this syncope is not known. The changes in hemodynamics are variable, including arrhythmias and myocardial ischemia, and one of the few consistent changes is a sudden fall in systemic and pulmonary arterial pressures (suggesting a reduced vascular resistance) followed by a decline in heart rate. The contribution of the cardioinhibitory and vasodepressor components of the RS to hemodynamics was evaluated by a computer model. This lumped-parameter computer simulation was based on equivalent electronic circuits (EECs) that reflect the hemodynamic conditions of a heart with severe AVS and a concomitantly decreased contractility as a long-term detrimental consequence of compensatory left ventricular hypertrophy. In addition, the EECs model simulated the resetting of the sympathetic nervous tone in the heart and systemic circuit during exercise and exercise-induced syncope, the fluctuating intra-thoracic pressure during respiration, and the passive relaxation of ventricle during diastole. The results of this simulation were consistent with the published case reports of exertional syncope in patients with AVS. The value of the EEC model is its ability to quantify the effect of a selective and gradable change in heart rate, ventricular contractility, or systemic vascular resistance on the hemodynamics during an exertional syncope in patients with severe AVS.

Pathophysiologie der Synkope

“…Anders herum können emotionale Belastungen oder andere vasovagale Trigger, wie ein postprandiales heißes Bad oder postprandiale körperliche Aktivität, bei diesen Patienten auch eine klassische VVS auslösen. In diesem Fall kann aber eine protrahierte Hypotension/Bradykardie fatale Folgen im Sinne eines hypoxämisch getriggerten Pumpversagens oder einer malignen Arrhythmie auslösen [24,25,26]. Umso deutlicher muss auf die Vermeidung entsprechender Trigger hingewiesen werden, um diese vasovagale Komponente verhindern zu können.…”