Abstract 17892: Strain Rate is Affected by Heart Rate in Younger Heart: A Simultaneous Invasive and Noninvasive in vivo Piglet Model
Introduction: In adult human and pig hearts, left ventricular (LV) systolic strain rate (SR) has been shown to be independent of heart rate (HR) in atrial tachycardia. It has been hypothesized that any increase in contractility related to the force-frequency relationship is balanced by a decrease in contractility due to reduced filling time and preload at higher HRs. In this study, we explore the impact of atrial tachycardia on SR of the young infant heart using a simultaneous invasive and noninvasive piglet model to determine whether SR of the immature heart is similarly not influenced by increasing HR.
Methods: Under general anesthesia (propofol, isoflurane), 1 - 15 day old piglets were instrumented intravascularly with Millar high-fidelity and pacing catheters in the left ventricle and right atrium, respectively. After stabilization, invasive hemodynamic and echocardiography parameters were acquired at baseline, and at 200, 230 and 260bpm. Basal circumferential SR was analyzed off-line by speckle tracking (frame rates 247±7 Hz). Each animal was its own control and repeated measure ANOVA was used for comparison, data is expressed as mean ± SE.
Results: Fourteen piglets of mean age 8.5±1.8 days, weight 3.6±0.5kg and baseline heart rate of 152±5bpm were assessed. Baseline LV systolic SR was -1.53±0.13 1/s and dP/dt 1656±115mmHg/s. With pacing, LV SR increased significantly (p = 0.002). The increase in SR mirrored the increase in contractility assessed invasively by dP/dt (p<0.001). M-mode LV end diastolic dimension decreased from baseline to 260bpm (73±9.9% of baseline value, p < 0.001) consistent with reduced preload with tachycardia.
Conclusion: Our study suggests that in the younger heart, SR is augmented by atrial tachycardia itself even in the presence of decreased preload. This is in keeping with preservation of the force frequency relationship. Given our findings, HR should be taken into account when assessing contractility using SR in young patients.
Author Disclosures: E. Fortin-Pellerin: None. L.K. Hornberger: None. J.Y. Coe: None. L. Mills: None. J. Serrano-Lomelin: None. P. Cheung: None. N.S. Khoo: None.
- © 2015 by American Heart Association, Inc.