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Beat-to-beat left ventricular performance in atrial fibrillation: radionuclide assessment with the computerized
Insights
Left ventricular ejection fraction varies significantly beat-to-beat in atrial fibrillation patients. A single ejection fraction measurement may underestimate true cardiac performance in these individuals.
Area of Science:
- Cardiology
- Nuclear Cardiology
- Cardiac Physiology
Background:
- Atrial fibrillation (AF) is associated with significant beat-to-beat variability in cardiac cycle length and left ventricular (LV) performance.
- Assessing LV function in AF patients requires methods capable of capturing this dynamic variability.
Purpose of the Study:
- To evaluate beat-to-beat LV ejection fraction (LVEF) and volumes in patients with atrial fibrillation using a nuclear probe.
- To determine the relationship between LV function, cycle length, and ventricular volumes in AF.
Main Methods:
- Utilized a computerized nuclear probe for continuous, beat-to-beat assessment of radionuclide time-activity curves.
- Analyzed 50 consecutive cardiac cycles in 18 AF patients with varying underlying conditions (mitral stenosis, regurgitation, coronary artery disease).
- Correlated nuclear probe-derived LVEF with multiple-gated cardiac blood pool imaging (MGCBP) in 14 patients.
Main Results:
- Demonstrated substantial beat-to-beat variation in cycle length and LVEF across all AF patients, irrespective of LV dysfunction severity.
- Found LV function was dependent on relative end-diastolic volume and preceding cycle lengths, but not preceding end-systolic volumes.
- Achieved excellent correlation (r=0.90) between beat-to-beat nuclear probe LVEF and MGCBP-derived LVEF.
Conclusions:
- A single LVEF value is insufficient to characterize LV function in patients with atrial fibrillation.
- Beat-to-beat analysis reveals dynamic LV performance influenced by filling volumes and preceding cycle lengths.
- Standard LVEF measurements may underestimate resting LV performance in AF patients.
Abstract:
There is wide beat-to-beat variability in cycle length and left ventricular performance in patients with atrial fibrillation. In this study, left ventricular ejection fraction and relative left ventricular volumes were evaluated on a beat-to-beat basis with the computerized nuclear probe, an instrument with sufficiently high sensitivity to allow continuous evaluation of the radionuclide time-activity curve. Of 18 patients with atrial fibrillation, 5 had mitral stenosis, 6 had mitral regurgitation, and 7 had coronary artery disease. Fifty consecutive beats were analyzed in each patient. The mean left ventricular ejection fraction ranged from 17 to 51%. There was substantial beat-to-beat variation in cycle length and left ventricular ejection fraction in all patients, including those with marked left ventricular dysfunction. In 14 patients who also underwent multiple gated cardiac blood pool imaging, there was an excellent correlation between mean ejection fraction derived from the nuclear probe and gated ejection fraction obtained by gamma camera imaging (r = 0.90). Based on beat-to-beat analysis, left ventricular function was dependent on relative end-diastolic volume and multiple preceding cycle lengths, but not preceding end-systolic volumes. This study demonstrates that a single value for left ventricular ejection fraction does not adequately characterize left ventricular function in patients with atrial fibrillation. Furthermore, both the mean beat-to-beat and the gated ejection fraction may underestimate left ventricular performance at rest in such patients.