Hypothesis 1) Myocardial function deteriorates due to a sudden increase in afterload following PDA ligation. 2) Myocardial Performance Index (MPI) is a load-dependent measure of cardiac function and therefore MPI would significantly change with ligation of the PDA.
Objective To test these hypotheses by evaluating the changes in systolic and diastolic function following PDA ligation.
Methods In this retrospective study all subjects were referred to the Center for Newborn and Infant Critical Care at Childrens Hospital Los Angeles for PDA ligation during a 9-month period in 2004. We reviewed the clinical data and the echocardiograms performed on each neonate within 6 hours before and immediately after PDA ligation. Assessment of myocardial function included load-dependent measures of contractility such as shortening fraction (SF) and heart-rate corrected velocity of circumferential fiber shortening (VCFc), a load-independent measure of contractility (relation of wall stress [WS] to VCFc), left and right cardiac output (CO), mitral and tricuspid in-flow Doppler, left ventricular tissue Doppler and MPI. Changes in afterload were assessed by measuring wall WS and calculating systemic vascular resistance (SVR).
Results Complete set of data was available in 8 patients that comprised the study group. All data are given as mean±SD. Birth wt 579±16 g, GA 25.6±1 wks, age at ligation 23±13 days. SF decreased from 39±8 to 30±7% (p= 0.01). SVR increased from 109±35 to 206±69 mmHg/ml/kg/min (p= 0.002). There was no change in VCFc (1.35±0.29 vs 1.33±0.42 circ/sec, p=0.4) and WS (17±6 vs 17±10 g/cm2, p=0.4). Left CO decreased from 361±103 to 199±62 ml/kg/min (p=0.001) while right CO did not change (from 395±159 vs 370±140 ml/kg/min (p=0.6). MPI increased from 0.22±0.09 to 0.65±0.27 (p=0.001).
Conclusions 1) There was an acute deterioration in both systolic and diastolic myocardial function immediately following ligation of the PDA. 2) There was a significant change in MPI suggesting load-dependency of this index of myocardial function.
Speculation The right CO did not change secondary to the presence of left to right shunt at the patent foramen ovale.