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).