Atrial supplydemand balance in healthy adult pigs: coronary blood flow, oxygen extraction, and lactate production during acute atrial fibrillation

Little is known about how atrial oxygen supply responds to increased demand, and under which conditions it falls short (supplydemand mismatch). Here, we have investigated the vasodilator response, oxygen extraction, and lactate production of the left atrium (LA) and left ventricle (LV) in response to atrial pacing and atrial fibrillation (AF). Series A (n 9 Dutch landrace pigs) was instrumented to measure LA and LV vascular conductance in branches of the circumflex artery. Coronary conductance reserve (CCR) was calculated as the ratio between conductance during adenosine infusion and baseline. Series B (n 7) was instrumented with sampling catheters in LA and LV veins for determination of blood gases and lactate levels. LA CCR (1.76 0.14) was significantly lower than LV CCR (3.16 0.27, P 0.002). However, basal oxygen extraction was lower in LA (27 3) than that in the LV (58 6, P 0.0006), indicating a larger extraction reserve in the LA than that in the LV (4.68 0.84 vs. 1.88 0.26, P 0.01). Atrial pacing caused an increase in LA conductance (Series A) and oxygen extraction (Series B). AF increased LA vascular conductance to 177 14 at 1 min, 168 14 at 5 min, and 164 31 at 10 min of AF (P 0.05 vs. baseline). Atrial oxygen extraction also increased from 26 3 at baseline to 63 5 (P 0.01) at 5 min and 60 11 (P 0.01) at 10 min of AF. Arterio-venous lactate difference increased significantly (P 0.02) during AF. In healthy pigs, the LA has a lower CCR, but a higher extraction reserve compared with the LV. Although both reserves were recruited during AF, atrial lactate production increased significantly.