Stretch-induced ventricular arrhythmias in isolated perfused rat hearts

Abstract

This study investigates the response of isolated Langendorff-perfused rat hearts to a rapidly applied left ventricular stretch from 20 % to 100 % of optimum volume. Left ventricular pressure time integral (PTI), cardiac electrogram, and oxygen consumption (!"# ) were measured and used as an index of mechanical activity, incidence of arrhythmias and energy expenditure, respectively. The integral of the ventricular pressure trace was used as an index of mechanical activity that was independent of heart rate. Arrhythmias developed immediately upon the stretch when the hearts were perfused with control Krebs-Henseleit (K-H) buffer, lasting for < 5 s. The standard deviation of the interbeat interval (SDRR) was obtained as a measure of the severity of the arrhythmias. The PTI and !"# were also increased by LV stretch. The !"# was maximal peak following the arrhythmias, showing a linear relationship with the severity of the arrhythmias. β-adrenergic stimulation and inhibition of prostaglandin formation decreased the stretch-induced arrhythmias (SDRR) by 58 ± 4.7 % (isoproterenol, P = 0.002, N = 4) and 23 ± 5.8 % (indomethacin, P = 0.0369, N = 5), respectively, compared to their pre-drug control. Chemical ablation (by Lugol’s solution) of the endocardial free running Purkinje fibres also decreased the stretch-induced arrhythmias by 48 ± 5.9 % (P < 0.0001, N = 8) compared to their Pre-drug control. The second part of this study investigated the response of isolated Purkinje fibres to mechanical stretch. Purkinje fibres were microdissected from the endocardial surface and mounted in a chamber on the stage of an inverted microscope for measurements of force and intracellular Ca2+ (fura-2/AM) before and during stretch. No change in intracellular [Ca2+] was observed when Purkinje fibres were stretched for 1 min. However, intracellular [Ca2+] increased when extracellular [Ca2+] was sequentially raised over a period of 5 minutes. Following these measurements, two isolated Purkinje fibres were fixed, immunolabeled with fluorescent antibodies for the transient receptor potential canonical channel 3 (TRPC3) and Factin and examined using confocal microscopy. The surface of the labelled Purkinje fibres showed distinct, round shapes which expressed a high level of TRPC3. Phalloidin labelling of F-actin was also present, and appeared to be in the central region of the fibres. In conclusion, my study has shown that stretching Purkinje fibres in the left ventricle gives rise to a short period of arrhythmias in isolated perfused rat hearts. Decreasing the interbeat interval via β-adrenergic stimulation decreases the likelihood of arrhythmias, along with decreased prostaglandin formation..