Case Reports Sinus Node Function and Electrophysiologic Alteration Following Superior-Septal Incision

Electrophysiologic study was performed in two cases in sinus rhythm who had mitral valve repair using superior-septal approach, in order to evaluate sin us node function and sinoatrioventricular conduction. Corrected sinus node recovery time ( <200 msec), and H-V intervals (<50 msec) were found in normal limits. Long P-A intervals were recognised. Maximum chronotropic response of the sinus node was excellent (169-199/min) in both cases. These findings support the elinical impression that sinus node function is well preserved although the sinus node artery is severed due to the superior-septal incic sion. P-R lengthening and different P wave morphology appeared on surface ECG compared to preoperative ECG findings. Superior-septal incision causes such ECG alterations probably due to the intraatrial conduction delay rather than either impaired sinus or AV nodal function. Activation propagation originating from atrial pacemaker complex goes only through the posterior preferential pathway because the anterior and middle ones were cut off. This single path to reach the AV node changes the e1ectrical veeter so that the P wave morphology becomes different, and causes intraatrial conduction delay with consequent PR segment prolongation. These findings, although limited with only two cases, may help understand electrophysiologic alterations following superior-septal incision. Further elinical studies involving electrophysiologic evaluation may encourage liberal use of this incision in cases with sinus rhythm.