Introduction: 

It is not well known what the effect of changing heart rate on coronary flow is in isolated unloaded hearts. Thus, our aim was to investigate the relationship between heart rate and coronary flow in isolated guinea pig hearts, and to examine whether the relationship is affected by variability of heart rate.

Methods: 

We recorded the ECG and coronary flow in the last 30 seconds of a 30-minute long control perfusion in isolated, Langendorff perfused guinea pig hearts. The average heart rate was calculated. The beat-to-beat variability of heart rate was quantified by calculating the root mean square of the successive differences of the RR intervals (RMSSD). Hearts were retrospectively allocated to a "Low" heart rate variability group (RMSSD < 3, n = 50 hearts) or to a "High" heart rate variability group

(RMSSD > 3, n = 36 hearts) based on the measured RMSSD values of the individual hearts.

Results: 

There was no significant difference in average heart rates between the "Low" and "High" heart rate variability groups. However, coronary flow values were significantly greater in the "High" heart rate variability group than in the "Low" heart rate variability group. We found a linear correlation between the average heart rate and the coronary flow in the "Low" as well as the "High" heart rate variability group. However, the regression lines were significantly different between the "High" and "Low" heart rate variability groups. The slope of the regression line was significantly greater in the "High" heart rate variability group than in the "Low" heart rate variability group; which resulted in higher coronary flow values in the "High" heart rate variability group than in the "Low" heart rate variability group in the physiological heart rate range.

Conclusions: 

There is a linear correlation between the average heart rate and the coronary flow in the isolated guinea pig heart, but the variability of heart rate influences the correlation. These results show that in the physiological heart rate range, an autonomic-independent coronary flow autoregulation occurs in the Langendorff (ex vivo - denervated) heart, mediated in part by increases in heart rate and, to a greater extent, by heart rate irregularity.