Percutaneous method for multiple epicardial monophasic action potential recordings during magnetocardiographic mapping in intact rats

A surgical approach for subdiaphragmatic programmed electrical stimulation (PES) in mice has been reported by Gutstein et al in 2003. We developed a percutaneous method to drive a patented magnetocardiography-compatible amagnetic catheter (AC), specifically designed for multiple monophasic action potentials (multiMAP) recording, at the epicardium of spontaneously breathing rats. The aim of this study was to test the feasibility of simultaneous magnetocardiographic (MCG) estimate of ventricular repolarization and multiMAP recording. Methods: Under fluoroscopic control, the AC was introduced with a sub-xyphoid puncture, in 5 anesthetized, spontaneously breathing, Wistar rats. The AC was moved at several epicardial sites until 4 stable MAPs were recorded, with a fixed inter-electrode distance of 1 mm. An unshielded 36-channel DC-SQUID system (sensitivity 20 fT/Hz½) was used to record the Bz component of cardiac magnetic field (MF). MAP signals, differentially amplified and filtered at DC-500 Hz, were digitized at 1kHz. The same AC was used for programmed PES at pacing cycles between 200 and 250 ms. Ventricular effective refractory period (VERP) was evaluated with the accuracy of 2 ms. MAP duration (MAPd) was measured, at 90% levels of repolarization. Results: Simultaneous MCG and MAP recordings were successful in all rats. One rat died for respiratory arrest. Four animals tolerated well the procedure and survived. One of them, still alive after 6 months, was restudied and survived also the second procedure. MAPd 90% and VERP (ms) were: 69±5.6 and 67±9.4, respectively, and corresponded to 75-90% of the QTend interval measured with MCG. Conclusion: This minimally invasive method is well tolerated, in most instances avoids animal sacrifice, and can be used to validate the accuracy of surface MCG estimate of dispersion of ventricular repolarization and for preclinical assessment of arrhythmogenic potential of new drugs