Effects of rapid atrial pacing on the arrhythmogenic activity of single cardiomyocytes from pulmonary veins - Implication in initiation of atrial fibrillation

Background-Pulmonary veins (PVs) are important sources of paroxysmal atrial fibrillation. Long-term rapid atrial pacing (RAP) changes atrial electroph ysiology and facilitates the maintenance of atrial fibrillation. It is not clear whether RAP alters the arrhythmogenic activity of PVs. The purpose of this study was to isolate single PV cardiomyocytes from control and RAP do gs and evaluate their electrophysiological. characteristics. Methods and Results-The action potential and ionic currents were investigat ed in PV cardiomyocytes from control and long-term (6 to 8 weeks) RAP (780 bpm) dogs by use of the whole-cell clamp technique. Dissociation of PVs yie lded rod-shaped single cardiomyocytes without (n=91, 60%) or with (n=60, 40 %) pacemaker activity. Compared with the control group, the RAP dog PV card iomyocytes had faster beating rates (0.86 +/-0.28 versus 0.45 +/-0.07 Hz, P <0.05) and shorter action potential duration. The RAP dog PV cardiomyocyte s with pacemaker activity have a higher incidence of delayed (59% versus 7% , P <0.001) or early (24% versus 0%, P <0.005) afterdepolarization. The RAP dog PV cardiomyocytes with pacemaker activity had smaller slow inward and transient outward but larger transient inward (0.017 +/-0.004 versus 0.009 +/-0.002 pA/pF, P <0.05) and pacemaker (0.111 +/-0.019 versus 0.028 +/-0.00 8 pA/pF, P <0.001) currents. The RAP dog PV cardiomyocytes without pacemake r activity had only smaller slow inward and transient outward and larger pa cemaker currents. Conclusions-PVs contain multiple cardiomyocytes with distinct electrophysio logical characteristics. RAP changes the electrophysiological characteristi cs and arrhythmogenic activity of PVs.