Abstract 12779: Increased Diastolic Untwisting Velocity in Response to Tachycardia as Evidence of Diastolic Reserve in the Young Infant Heart: A Simultaneous Invasive and Noninvasive in vivo Swine Model
Introduction: In response to exercise, the healthy adult left ventricle (LV) augments its filling through early untwisting, creating suction even before the AV valve opens. The role of untwisting in the immature heart remains controversial. Older infants have delayed and decreased LV untwisting rates at baseline, suggesting untwisting may play less of a role in LV filling at least at rest. Although no in vivo data exists, one in vitro investigation of human infant myocardium has suggested relaxation may be augmented during tachycardia which could suggest an element of diastolic reserve. In the present study, we sought to explore the diastolic function response to atrial tachycardia in a young piglet model.
Methods: Under general anesthesia (propofol, isoflurane), 1-15 day old piglets were instrumented intravascularly with Millar high-fidelity and pacing catheters in the LV and right atrium (RA), respectively. After stabilization, invasive hemodynamic and echocardiography parameters were acquired at baseline and at 230bpm (30-40% above baseline). LV twist was analyzed off-line by speckle tracking (226 ± 55 frames/s). Subjects were their own control and paired t-tests were used for comparisons after confirmation of normal distribution for each variable. Values were expressed as mean ± SD.
Results: Eight piglets of mean age 8.6 ± 6.8 days and weight 3.6 ± 2.18kg, and baseline heart rate of 157 ± 18bpm were assessed. With tachycardia, Tau decreased from 28 ± 9ms to 23 ± 9ms (p = 0.03). Peak untwisting rate increased from -247 ± 83 to -412 ± 179 degrees/s (p = 0.04) and the change correlated with Tau (r=0.45, p=0.04). Untwisting rate during isovolumic relaxation also increased from -146 ± 74 deg/s to -335 ± 205 deg/s (p = 0.03). There was a trend towards reduction in LV end diastolic pressure from 13 ± 6 to 10 ± 5 mmHg (p = 0.067).
Conclusion: The early infant heart has the capacity to maintain normal LV filling pressures during atrial tachycardia, and this is associated with increased LV untwisting performance suggesting diastolic reserve. The boundaries of this diastolic reserve, and whether this knowledge can be exploited to augment LV filling in the critically ill infant is the subject of ongoing investigations.
Author Disclosures: E. Fortin-Pellerin: None. L. Mills: None. J.Y. Coe: None. N.S. Khoo: None. P.Y. Cheung: Research Grant; Significant; Grant from Canadian Institutes of Health Research (Grant title: The cardiovascular support for neonates with hypoxic and reoxygenation injury). L.K. Hornberger: None.
- © 2014 by American Heart Association, Inc.