Cardiovascular topics 36 AFRICA A Comparison of Stimulation Frequency and Electro-Augmentation on Myocardial Function, Extensibility, Coronary Flow Rate, Oxygen Consumption and Glucose Metabolism

Abstract. The effects of increased heart rate on the function and metabolism of the isolated perfused rat heart were studied. Single stimuli as well as paired and coupled stimuli were used to increase the heart rate from 80 to 200 beats/min. Heartblock was produced in the rat heart to give a preparation with a heart rate of 80 beats/min. For measurements of mechanical activity a modified Langendorf perfusion system with a myographic force transducer was used. Results indicate that tension development was greater with paired than with single stimuli at frequency rates of 100−160 beats/min. At higher frequency rates there wa.s no difference between single and paired stimuli. However, paired stimuli increased the tension developed per min. (TTM) for all rates studied, whereas they reduced the time to peak height of developed tension for rates up to 160 beats/min. Relationships or length to tension a