We studied the origins of ectopic beats during low-flow reperfusion after acute regional ischemia in excised rat hearts. The left anterior descending coronary artery was cannulated. Perfusate was delivered to the cannula using an high-performance liquid chromatography pump. This provided not only precise control of flow rate but also avoided mechanical artifacts associated with vessel occlusion and deocclusion. Optical mapping of epicardial transmembrane potential served to identify activation wavefronts. Imaging of NADH fluorescence was used to quantify local ischemia. Our experiments suggest that low-flow reperfusion of ischemic myocardium leads to a highly heterogeneous ischemic substrate and that the degree of ischemia between adjacent patches of tissue changes in time. In contrast to transient ectopic activity observed during full-flow reperfusion, persistent ectopic arrhythmias were observed during low-flow reperfusion. The origins of ectopic beats were traceable to areas of high spatial gradients of changes in NADH fluorescence caused by low-flow reperfusion.

We describe a new approach that combines several techniques to allow abnormal electrical and calcium activity to be visualized within hypoperfused myocardial tissue. A flexible microcannula was inserted into the left anterior descending artery of Langendorff perfused rat hearts, an air-tight seal between the coronary artery and the cannula was created, and an HPLC pump was used to deliver a specified flowrate through the microcannula. High resolution optical mapping of NADH/ calcium, NADH/voltage or calcium/voltage was then conducted using a dual camera system. The ECG was acquired using surface electrodes. This perfusion technique is superior to occluding a vessel by either a tie or a clamp because it allows precise control of the composition and amount of flow to a defined ischemic bed. Another advantage is that flow can be stopped and resumed remotely, without touching the heart. This allows ectopic beats, or other arrhythmogenic activity, such as alternans, to be recorded immediately after changes in flow are imposed. Altogether, the described method provides a powerful new tool to assess how coronary flow rate affects the degree of local ischemia by the ability to record abnormal patterns of electrical activity and associated intracellular calcium transients with high spatiotemporal resolution from epicardial areas as small as 100 × 100 μm.