MAP, ECG and atrial arrhythmia recordings in isolated hearts
The atrial MAPs, pseudo–12-lead electrocardiograms (ECGs), and coronary perfusion pressure were continuously monitored and digitized in real time. Pressure-contact Ag-AgCl MAP electrodes were placed on the endocardium of left auricular appendage. Atrial MAP profiles were analyzed using software (Spike2 version 6.03, CED, UK) to determine the MAP duration at which repolarization was 90% completed (MAPD90). The atrial effective refractory period (ERP) and arrhythmic events were induced by the S1S2 and S1S1 (burst protocol) programmed stimulations. ECG parameters were measured from a superimposition of 12-lead ECG recordings. Spontaneous sinus heart rate was measured from an average of 10 atrial beats when the rhythm was regular without arrhythmias.
An extra-atrial beat (EAB) was defined as a spontaneous beat occurring earlier than the next regular (spontaneously beating heart) or pacing (paced heart) beat. Atrial tachycardia (AT) was defined as a sequence of three or more consecutive, relatively regular spontaneous atrial beats occurring unexpectedly at a rate exceeding the spontaneous or pacing rate. An episode of AF was defined as a sequence of fast, irregular atrial signals in MAP and ECG recordings with irregular QRS complexes in a 12-channel ECG record. ATs and AFs were collectively referred to as atrial arrhythmic events/arrhythmias. Post-repolarization refractory period (PRR) was calculated using an equation of (ERP – MAPD90).