Alternans in Rabbit Heart During Acute Regional Ischemia: Optical Mapping and Microelectrode Recordings

Abstract

T-wave alternans during acute ischemia have been determined as a precursor of ventricular arrhythmias usually resulting in sudden cardiac death. Optical mapping is often used to investigate the mechanisms of alternans in heart preparations. Several hypothesis exist that may explain the formation of optical alternans. One of them is that optical action potential amplitude (OAPA) alternans may indicate the formation of alternating conduction blocks. In our study by using optical mapping simultaneously with microelectrode recordings we aimed to investigate the occurrence of OAPA alternans during acute regional ischemia and to determine the electrical origin underlying the alternans formation. Experiments were performed in Langendorff-perfused rabbit hearts stained with near-infrared dye di-4-ANBDQBS. Optical signals were registered from left ventricle epicardium. The hearts were stimulated by applying 300 ms, and 200 ms pacing cycle. Results showed that OAP started alternate with high and low amplitudes at 200 ms pacing at early ischemia (4-6 minutes). The alternation zone migrated, shrank and finally disappeared with increasing ischemia time. In order to elucidate the mechanism of this phenomenon two glass microelectrodes were used to examine electrical activity by registering action potentials from subepicardial and deeper (3-5 mm) myocardial layers simultaneously. Microelectrode recordings revealed that OAPA alternans is the result of 2:1 conduction blocks in a certain layer whilst the regular response is held in the other layers. During later ischemia (10-15 minutes) deep myocardial layers lose their excitability remaining optical signals only with low amplitude. It explains the disappearing of OAPA alternans. Thus, our experimental data show that OAPA alternans which arise during the early acute ischemia can be caused by alternation of conduction blocks in a certain myocardial layers.Research is funded by the European Social Fund under the Global Grant measure.