Quantification of the atrial contribution to diastolic filling during radionuclide angiography.

To define exactly the onset of late diastolic filling with respect to atrial contraction, the atrial contribution (AC) to left ventricular filling was quantified in 34 patients with a variety of diseases using radionuclide angiography. From the time-activity curve and its first derivative, a flow-volume loop was constructed. Using the flow-volume loop, the period between minimal flow and the moment of maximal end-diastolic counts was defined as the AC-interval and correlated with the PQ-interval on the electrocardiogram. The relative filling volumes within these time periods were closely related in all patients (r = 0.99, P < 0.0001). The correlation between the PQ-interval and AC-interval was also statistically significant (r = 0.82, P < 0.0001). In a subset of patients, the PQ-interval and AC-interval were not exactly the same. In these patients, the AC-interval was always longer than the PQ-interval, indicating the existence of passive diastasis flow before the onset of atrial contraction. This was more apparent in patients with low heart rates than in those with high heart rates. Despite the close correlation between the PQ-interval on the electrocardiogram and the AC-interval of the flow-volume loop, they may represent different entities. We conclude that the PQ-interval is better than the AC-interval for determining the moment of onset of atrial activity during radionuclide angiography.