Influence of sequence of atrial and ventricular systoles on closure of mitral valve.

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Abstract
A concentric catheter assembly was passed into the left heart through the fossa ovalis. The inner catheter for ECG-synchronized injections of indocyanine green into the left ventricle was positioned so that its spray tip was 0.5-2.0 cm downstream to the mitral valve. The outer catheter for sampling of dilution curves was positioned so that its tip was 0.5-1.0 cm upstream to the valve. Slight retrograde flow of indicator was detected uniformly in dogs with normal sinus rhythm with these catheter positions, but not when the positions were separated appreciably farther. The atria and ventricles were driven by coupled pacemakers in any desired temporal sequence. Varying the sequence of atrial and ventricular contractions from normal to synchronous, or reverse sequence, while the heart rate ranged from 60 to 200 beats/min. caused increases in atrial pressure''s and decreases in cardiac output. However, a systematic effect on the efficiency of mitral valve closure could not be demonstrated. Similarly, when the atria were fibrillating no increase in retrograde flow was detected.