Objective: Right atrial dilation occurring late after the modified Fontan procedure is frequently associated with low output states, supraventricular arrhythmias, and atrial thrombus formation. We addressed the hypothesis that progressive right atrial dilatation contributes to inefficient right heart flow dynamics.
Methods: Modified atriopulmonary connections were performed on explanted isolated sheep heart preparations with various degrees of surgically induced right atrial dilatation (right atrial volumes 6 to 55 cm3). Flow models were perfused in an in vitro flow loop with the use of a blood analog fluid. A fluid energy balance was performed for six flow rates (1.0 to 6.0 L/min) at each degree of right atrial dilatation, and the rate of total fluid energy loss was calculated and expressed as a function of right atrial volume and flow rate. Effective pressure drop and fluid resistance across the right atrial chamber were also determined for each flow condition.
Results: The rate of fluid energy loss increased with increasing right atrial dilatation and flow rate for all conditions studied (p < 0.001). Over the range of right atrial volumes and flow rates examined, the average increase in the rate of energy loss was 3.8- and 117-fold, respectively. Calculated fluid resistance through the right atrium also increased with increasing right atrial volume and flow rate (p < 0.001), exhibiting an average increase of 3.2- and 3.3-fold respectively.
Conclusions: Right atrial dilatation in atriopulmonary connections causes fluid energy losses and increases the energy required to move blood from the venae cavae to the pulmonary arteries. These observations may help explain the progressive nature of late failures of atriopulmonary connections and provide additional rationale for conversion from atriopulmonary connections to lateral tunnel total cavopulmonary connections in selected patients.