Characteristics of Subsidiary Pacemaker in Complete Heartblock with Narrow QRS Complex

ABSTRACT

BACKGROUND: The stability of A-V junctional rhythm is the most important clinical interest in the patients with the complete heart block with narrow QRS complex. The QRS morphology, the basal heart rate & the reponse of subsidiary pacemaker to drugs may be helpful to assess the stability. But it can not be assessed exactly. The recording of the His-bundle was thought to be a means of predicting the clinical course of the patients and the necessity of the artificial pacemaker insertion;also it can assess the A-V block site. But it is invasive study cannot assessed exactly the stability of subsidiary pacemaker. To investigate the characteristics of subsidiary pacemaker, we studied the responses of the artificial pacemaker to ventricular overdrive suppression and the drugs by used the artificial pacemaker in the patient with the complete heart block with the narrow QRS complex, which can be accepted as "stabli" in general. METHOD: There was total of 11 patients diagnosed with the complete AV block with the narrow QRS complex(the escape junctional rhythm was less than 0.10sec) at the Yeungnam University Hospital from May 1988 to June 1989. To investigate the ventricular overdrive suppression of subsidiary pacemaker, the response of the subsidiary pacemaker after IV administatin of drugs (atropine, isoproterenol, lidocaine) and the junctional recovery time were measured. RESULTS: Thtee patterns were obtained in the overdrive suppression test (fig.1). The recovery time of the subsidiary pacemaker was 364.5+/-212.15% of the basal R-R interval. Among seven of the eight patients who showed syncoped, the JRTmax were 3 times higher than the basal R-R interval. In one of eight, CJRT which represent the absolute time, was prolonged to 560 msec. In one case, we examined overdrive suppression test serially was which shows gradual decrement of junctional recovery time, and normal sinus rhythm was recovered at the 14th after the development of complete heart block. After VOS, the junctional recovery time of the subsidiary pacemaker was 364.5+/-212.1% of basal R-R interval in complete heart block group. After injection of atropine, the decrement of R-R interval was 5.51+/-3.88% of basal R-R interval. After injection of isoproterenol, the decrement of R-R interval was 32.76+/-8.09% of basal R-R interval. Marked increase of the basal heart rate was observed. After injection of lidocaine, the increment of R-R interval was 1.72+/-1.82% of basal R-R inteval. CONCLUSION: The results suggest that measurement of the junctional recovery time following overdrive suppression is useful for evaluation of stability of subsidiary pacemaker. And also the subsidiary pacemaker shows the better response to sympathomimetic agent than to parasympathetic blocker.