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Right bundle branch block (RBBB) is frequently observed in congenital, valvular and ischemic heart diseases in addition to chronic obstructive pulmonary disease. However, RBBB in young generation is m...ainly based on the physiologic right ventricular volume overload leading to stretch of right bundle branch. This indicates that RBBB may be periodic in some cases depending on respiratory phase, because intrathoracic pressure and systemic venous return vary periodicaly due to respiration. Here, we present four cases of university students showing cyclic RBBB in standard electrocardiogram (ECG) recorded in the annual health check-up program. ECG in the first three male students demonstrated remarkable respiratory sinus arrhythmia and RBBB limited under tachycardia presumably due to inspiration. Because cardiac vagal nerve activity is known to be inhibited by lung inflation. ECG in the fourth male student showed transient RBBB independent of heart rate. ECG in all these students commonly showed vertical or mild right QRS axis. They were all slender and physically active. Physiologic respiratory splitting was heard in their second heart sounds, suggesting that congenital cardiac anomalies are unlikely. So far, functional RBBB has been reported during tachyarrhythmia, and vagaly mediated negative dromotropism is well known. Respiratory RBBB is considered to be attributable mainly to cyclic right ventricular expansion in addition to rate-dependent functional block of right bundle branch synchronized by inspiration (first three cases) or negative dromotropic actions based on juvenile vagotony without macroscopic heart rate variability (fourth case). Therefore, intermittent RBBB depending on respiration is concluded to be a normal variant.show more
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