HEMODYNAMIC-EFFECT OF PROGRESSIVE RIGHT ATRIAL DILATATION IN ATRIOPULMONARY CONNECTIONS

Right atrial dilation occurring late after the modified Fontan procedu re is frequently associated with low output states, supraventricular a rrhythmias, and atrial thrombus formation, We addressed the hypothesis that progressive right atrial dilatation contributes tit inefficient right heart flow dynamics, Methods: Modified atriopulmonary connection s were performed on explanted isolated sheep heart preparations with v arious degrees of surgically induced light atrial dilatation (right at rial volumes 6 to 55 cm(3)), Flow models were perfused in an in vitro flow loop with the use of a blood analog fluid, A fluid energy balance was pet-formed for six flow rates (1.0 to 6.0 L/min) at each degree o f right atrial dilatation, and the I-ate of total fluid energy loss wa s calculated and expressed as a function of right atrial volume and fl ow 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, respective ly, Calculated fluid resistance through the right atrium also increase d with increasing right atrial volume and flow rate (p < 0.001), exhib iting an average increase of 3.2- and 3.3-fold respectively. Conclusio ns: Right atrial dilatation in atriopulmonary connections causes fluid energy losses and increases the energy required to move blood from th e venae cavae to the pulmonary arteries. These observations mag help e xplain the progressive nature of late failures of atriopulmonary conne ctions and provide additional rationale for conversion From atriopulmo nary connections to lateral tunnel total cavopulmonary connections in selected patients.