Pediatric and Congenital Heart Disease Session 2: Frontiers in Single Ventricle Heart Disease (2020)-Physiologic Insights into the Fontan Circulation by Stress Imaging

Physiologic Insights into the Fontan Circulation by Stress Imaging

Video Transcription

Video Summary

The talk explains the physiology of the Fontan circulation, focusing on why these patients often have limited exercise capacity. The speaker argues the main issue is not poor cardiac contractility, since ejection fraction and load-independent measures of function are often fairly normal, but impaired preload from the Fontan setup. In a normal circulation, venous return is driven by a pressure gradient; in Fontan patients, the absence of a subpulmonary ventricle raises the resistance to venous return, so filling the ventricle becomes difficult. The body compensates by increasing venous pressure and shifting blood from unstressed to stressed volume, often via mechanisms like the renin-angiotensin-aldosterone system. The talk also discusses MRI-based stress tests, including exercise, dobutamine, and sildenafil studies, to measure cardiac and pulmonary responses. Overall, the key message is that Fontan physiology is limited primarily by abnormal loading conditions and impaired venous return, not intrinsic pump failure.

Keywords

Fontan circulation

exercise capacity

preload impairment

venous return

cardiac MRI stress testing

pulmonary hemodynamics