Normalized peak filling rate (PFR), as derived from the radionuclide angiographic time-activity curve, is widely utilized in the investigation of diastolic performance of the intact heart. Because the nuclear technique reveals only relative and not absolute volume changes, the raw value of PFR, derived in counts per second, must be """"""""normalized"""""""", or expressed in terms of a volume parameter obtained from the time activity curve. Most commonly, this is expressed as end-diastolic volumes per second. However, this makes the determination of PFR dependent on both end-diastolic volume as well as ejection fraction. The purpose of our investigation was to study the impact of alternative normalization parameters on results of previous studies which had used PFR normalized by end-diastolic volume. For intergroup comparisons between normal subjects and patients with hypertrophic cardiomyopathy, alternative normalization parameters importantly affected the group comparisons, owing to the large differences in the parameters between the groups (i.e. end-diastolic or end-systolic volume). For serial comparison of patients before and after an intervention, the direction, magnitude and statistical significance of the changes in PFR were almost always maintained with different normalization parameters. Our results indicate the importance of evaluating changes in the normalization parameter itself between groups or during an intervention, before changes in the normalized PFR may be ascribed to changes in diastolic performance.
