MECHANOELECTRIC FEEDBACK IN THE ATRIUM OF THE ISOLATED GUINEA-PIG HEART

Objectives: Atrial arrhythmias are prevalent during clinically abnorma l myocardial loading, e.g. when the atrium is dilated or stretched. Th e initiating cause of the first premature beat that leads to this arrh ythmia is unclear, as are the reasons for sustaining it. One possibili ty is that abnormal mechanical factors induce electrophysiological cha nges conducive to arrhythmia via 'mechanoelectric feedback'. The aim o f this study is to investigate the concept that atrial stretch modulat es the electrophysiological properties of the atrium via mechanoelectr ic feedback, and that mechanoelectric feedback can produce atrial arrh ythmias. Methods: Guinea-pigs were humanely killed by cervical disloca tion and the hearts removed and perfused with oxygenated Krebs-Hensele it solution by the Langendorff method. The heart was paced at an atria l site near the sinus node. Monophasic action potentials and electroca rdiograms were recorded from the left atrium and left ventricle with s uction electrodes. Transient stretch was induced by inflating a fluid- filled intra-atrial latex balloon catheter. Results: Increase in atria l volume produced several significant changes in the epicardial monoph asic action potentials. It produced (i) decreases in the amplitude; (i i) a decrease in duration from 62.55 to 51.95 ms measured at 50% repol arisation (10.6 +/- 3.6 ms, P < 0.05, n = 6); (iii) an increase in dur ation from 122.45 to 140 ms measured at 90% repolarisation (17.55 +/- 4.5 ms, P < 0.05, n = 6) -- due to the presence of early afterdepolari sations. (iv) These load-induced electrophysiological changes coincide d with the occurrence of arrhythmia or premature atrial beats. Conclus ions: Load changes in the atrium can produce electrophysiological chan ges of a kind that may be relevant to clinical atrial arrhythmia.