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Atrial systole enhances intraventricular filling flow propagation during increasing heart rate
Arvind Santhanakrishnan1, Ikechukwu Okafor2, Gautam Kumar3
1School of Mechanical and Aerospace Engineering, Oklahoma State University, 218 Engineering North, Stillwater, OK 74078, USA; Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology & Emory University, 315 Ferst Drive, Atlanta, GA 30332, USA.
Insights
Increasing heart rate (HR) diminishes early filling vortex propagation in the left ventricle (LV), elevating the role of atrial contraction for diastolic filling. This impacts understanding cardiac function and disease diagnostics.
Area of Science:
- Cardiovascular Physiology
- Fluid Dynamics
- Biomedical Engineering
Background:
- Diastolic left ventricular (LV) function is crucial for cardiac health and disease diagnosis.
- The effect of increasing heart rate (HR) on intraventricular vortex flow patterns remains unclear.
- Previous research noted a diminished E/A ratio with increasing HR, but vortex dynamics were not fully elucidated.
Purpose of the Study:
- To investigate how intraventricular vortex flow patterns change with increasing heart rate (HR) under constant transmitral E/A ratio.
- To test the hypothesis that increased HR diminishes the contribution of early filling (E-wave) to vortex propagation.
- To provide insights into diastolic fluid dynamics relevant to clinical conditions.
Main Methods:
- Utilized a physiologic in vitro flow phantom simulating the left ventricle (LV).
- Varied heart rate (HR) across 70, 100, and 120 beats per minute (bpm) with a constant E/A ratio (1.1-1.2).
- Employed 2D particle image velocimetry to analyze intraventricular flow patterns in longitudinal planes.
Main Results:
- Observed counter-rotating vortices during early filling (E-wave) across all tested heart rates (HRs).
- Found diminished vortex propagation during E-wave and amplified secondary vorticity production by atrial systole with increasing HR.
- Noted a delay in peak vortex circulation timing with increasing HR, occurring near the end of atrial systole (A-wave) at 120 bpm.
Conclusions:
- Elevated heart rates (HRs) reduce the contribution of early diastolic filling to vortex propagation in the left ventricle (LV).
- Atrial systole plays an increasingly significant role in LV filling at higher heart rates due to time constraints.
- The findings offer a foundation for studying diastolic dysfunction in conditions with impaired exercise tolerance.
Abstract:
Diastolic fluid dynamics in the left ventricle (LV) has been examined in multiple clinical studies for understanding cardiac function in healthy humans and developing diagnostic measures in disease conditions. The question of how intraventricular filling vortex flow pattern is affected by increasing heart rate (HR) is still unanswered. Previous studies on healthy subjects have shown a correlation between increasing HR and diminished E/A ratio of transmitral peak velocities during early filling (E-wave) to atrial systole (A-wave). We hypothesize that with increasing HR under constant E/A ratio, E-wave contribution to intraventricular vortex propagation is diminished. A physiologic in vitro flow phantom consisting of a LV physical model was used for this study. HR was varied across 70, 100 and 120 beats per minute (bpm) with E/A of 1.1-1.2. Intraventricular flow patterns were characterized using 2D particle image velocimetry measured across three parallel longitudinal (apical-basal) planes in the LV. A pair of counter-rotating vortices was observed during E-wave across all HRs. With increasing HR, diminished vortex propagation occurred during E-wave and atrial systole was found to amplify secondary vorticity production. The diastolic time point where peak vortex circulation occurred was delayed with increasing HR, with peak circulation for 120bpm occurring as late as 90% into diastole near the end of A-wave. The role of atrial systole is elevated for higher HR due to the limited time available for filling. Our baseline findings and analysis approach can be applied to studies of clinical conditions where impaired exercise tolerance is observed.
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