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A 70-year-old Japanese woman was admitted to our hospital because of transient second degree atrioventricular (AV) block. An electrophysiologic study (EPS) was performed, and Mobitz type II infra-Hisian block during atrial pacing at a rate of 130/min was noted. An AV nodal reentrant tachycardia (AVNRT) was induced by ventricular pacing at a rate of 180/min, and 2:1-3:1 infra-Hisian block during AVNRT was observed. The AV block and AVNRT rarely occurred in the clinical setting, and the patient did not complain of any symptoms related to these arrhythmias. Therefore, the patient refused permanent pacemaker implantation, although she continued to be followed in our outpatient clinic. However, the patient was re-admitted one year later because of palpitations and dyspnea upon exertion related to the AV block. The 12-lead ECG showed high degree AV block with narrow QRS complexes. The patient underwent pacemaker implantation during the subsequent hospitalization, and her symptoms improved postoperation. AV block during AVNRT is sometimes observed, and it has been considered as a functional AV block. In the present case, a pathologic conduction disturbance in the His-Purkinje system caused the high degree AV block during AVNRT. The high degree AV block during AVNRT may indicate the existence of a conduction disturbance in the His-Purkinje system in some of these types of cases.

Unlabelled: The purpose of this study was to examine the long-term course of conductivity in patients with second- or third-degree atrioventricular (AV) block after pacemaker implantation. Fifty-four patients (30 males and 24 females, mean age 59.5 years) had a 12-lead electrocardiogram (ECG) recorded prior to pacemaker implantation and again after a follow-up of more than 5 years (mean 108 months). The degree of AV block and the morphology of the QRS complex in the two ECGs were compared. Twenty-eight (85%) of the 33 patients with complete AV block and 15 (71%) of the 21 patients with second-degree AV block before implantation showed complete AV block after the follow-up period. The progression of AV block was recognized only in patients with intra-His (BH) or infra-His (H-V) block. In 29 patients, escape QRS complexes were recorded in both ECGs. A change in the QRS complex was noted in 6 patients (21%), including 2 with new bundle branch block (BBB), 2 with wider BBB, 1 with new left axis deviation, and 1 with a change to another BBB. This change was particularly notable in the H-V block group (44%)., In Conclusion: (1) Most patients with complete AV block did not recover AV conductivity after the long-term follow-up. (2) Second-degree BH and H-V block tended to progress to complete AV block.

Three patients who had undergone implantation of a rate modulated, atrial sensitive RS4 pacemaker, with a single orthogonal lead underwent replacement of a depleted unit with a DDD pulse generator, reusing the original lead with an adapter that allowed conversion of the bipolar atrial electrode into unipolar configuration. The mean atrial electrogram amplitude was 1.8 mV and no significant atrial sensing defects were found during Holter monitoring. As the RS4 pulse generator is no longer available, continued VDD pacing is possible by replacing it with a DDD pulse generator using the previously implanted single lead system.

To clarify the clinical significance of an abnormally prolonged paced QRS duration, we studied 114 patients who had undergone pacing for atrioventricular block (AVB). Patients were divided into two groups: group I consisted of 29 patients with at least one paced QRS duration greater than or equal to 180 msec during the follow-up period; group II consisted of 85 patients with paced QRS durations less than 180 msec. The clinical background, QRS complexes before pacing, and the echocardiographic findings were assessed. Males (P less than 0.05), those with H-V block (P less than 0.05) and a wider QRS complex of conducted and escape beats (both P less than 0.01) were dominant in group I. The incidence of underlying heart disease was greater in group I than in group II (83% vs 32%, P less than 0.01). Reduced left ventricular ejection fraction (LVEF) and increased left ventricular end-diastolic dimension (LVDd) were more prominent in group I than in group II (LVEF 0.49 +/- 0.17 vs 0.68 +/- 0.10, P less than 0.01, LVDd 57.1 +/- 7.9 mm vs 48.5 +/- 5.6 mm, P less than 0.01). The paced QRS duration correlated with LVEF (r = -0.61) and LVDd (r = 0.81). A paced QRS duration greater than or equal to 180 msec was sensitive and specific for a LVEF less than 0.5 (83.3% and 85.2%) and LVDd greater than or equal to 60 mm (100% and 81.4%). We conclude that patients with a prolonged paced QRS duration have more serious heart disease, and the paced QRS duration can be a useful indicator of impaired LV function.