The First Heart Sound in Complete Heart Block

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Abstract
Eight subjects with complete atrioventricular heart block were studied with simultaneous echocardiography and phonocardiography to investigate the role of the mitral and tricuspid valves in the genesis of the first heart sound (S 1 ). Mitral valve motion was studied in all cases and tricuspid patterns in three. At P-R intervals less than 0.20 sec, mitral leaflet closure was completed by ventricular systole. Below P-R values of 0.20 sec there was an inverse relationship between P-R and S 1 amplitude. With P-R between 0.20 and 0.50 sec atrial systole closed the mitral valve without recordable sound. Beyond P-R intervals of 0.50 sec there was reopening of the mitral valve and secondary closure initiated by ventricular systole which was coincident with S 1 . The extent of mitral leaflet separation at the onset of ventricular systole correlated with S 1 amplitude. Pre-ejection period was not related to S 1 intensity. Over a wide range of P-R intervals in two subjects with a split S 1 , tricuspid valve closure was simultaneous with the second S 1 component. It was concluded that atrioventricular valve closure is a necessary event in the production of S 1 and that at least in some individuals tricuspid valve closure is related to its second high frequency component.