Echocardiography-based selection of quiescent heart phases: implications for cardiac imaging

We compared the potential effectiveness of echocardiography with electrocardiography (ECG) for the selection of phases within the cardiac cycle during which there is relatively little motion. Determination of such phases may be important for triggering other modalities such as computed tomography and magnetic resonance imaging.

In a preliminary study in 2 volunteers, simultaneous ECG and cardiac echocardiographic data were obtained and analyzed. Various phases of the echocardiographic data were cross-correlated from beat to beat. Time point pairs from different cardiac cycles with correlation of 0.8 were selected.

Beat-to-beat correlation values peaked at around 80% of the R-R' interval near the cardiac apex and around 30% of the R-R' interval near the cardiac base for 1 subject. For the other subject, the correlation values peaked at around 75% of the R-R' interval near the cardiac apex.

The cardiac cycle phase having maximum spatial cross-correlation for the longest period varied from subject to subject and also on the portion of the heart that was being imaged. Echocardiography may be superior to ECG in determining points in the cardiac cycle when the heart is relatively stationary and can potentially provide more optimal triggering information for cardiac computed tomography or magnetic resonance imaging.