A comparison of stimulation frequency and electro-augmentation on myocardial function, extensibility, coronary flow rate, oxygen consumption and glucose metabolism.

Abstract

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 was 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 of length to tension at different rates of stimulation were also determined. Myocardial oxygen consumption and coronary flow rates increased with increasing heart rate, with both single and paired stimuli. Paired stimulation caused significantly greater oxygen consumption at all frequency rates, while the increase in coronary flow rate was similar with paired and single stimuli. The effects of increasing heart rate by single and paired stimuli on the metabolism of [U‐14C] glucose were studied. Glucose uptake and lactate production were significantly higher with paired than with single stimuli at a constant heart rate. Paired and single stimuli had a similar effect on the pattern of glucose metabolism with increased heart rate.The results suggest, in agreement with the suggestion made by other workers, that the potentiating effects of paired stimuli dependent on the interval‐strength relationship of the impulses and are probably related to the optimal availability of Ca++ at the contractile sites. Furthermore, the increased oxygen consumption, the limited increase in coronary flow rate and the reduced effect of paired stimulation on tension development at higher rates of stimulation make it doubtful whether this procedure can be used for therapeutic purposes in the failing heart.