Fetal cardiac surgery may improve the prognosis of certain complex congenital heart defects that have significant associated mortality and morbidity in utero or after birth. An important step in translating fetal cardiac surgery is identifying potential mechanisms leading to myocardial dysfunction following bypass. The hypothesis was that fetal cardiac bypass results in myocardial dysfunction, possibly due to perturbation of calcium cycling and contractile proteins.
Mid-term sheep fetuses (n=6) underwent 30 minutes of cardiac bypass and 120 minutes of monitoring after bypass. Sonomicrometry and pressure catheters inserted in left (LV) and right ventricles (RV) measured myocardial function. Cardiac contractile and calcium cycling proteins, along with calpain, were analyzed by immunoblot.
Preload recruitable stroke work (slope of the regression line) was reduced at 120 min after bypass (RV – baseline vs. 120 min after bypass, 38.6±6.8 vs. 20.4±4.8 (P=.01); LV – 37±7.3 vs. 20.6±3.9 (P=.01). Tau (msec), a measure of diastolic relaxation, was elevated in both ventricles (RV – baseline vs. 120 min after bypass, 32.7±4.5 vs. 67.8±9.4 (P<.01); LV – 26.1±3.2 vs. 63.2±11.2 (P=.01). Cardiac output was lower and end-diastolic pressures were higher in the RV, but not the LV, after bypass compared with baseline. RV troponin I was degraded by elevated calpain activity and protein levels of sarco(endo)plasmic reticulum calcium ATPase (SERCA2a) were reduced in both ventricles.
Fetal cardiac bypass was associated with myocardial dysfunction and disruption of calcium cycling and contractile proteins. Minimizing myocardial dysfunction after cardiac bypass is important for successful fetal surgery to repair complex congenital heart defects.