© 2002 by European Society of Cardiology
Copyright © 2002, European Society of Cardiology
Relation between local myocardial growth and blood flow during chronic ventricular pacing*
aDepartment of Physiology, Cardiovascular Research Institute Maastricht, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands
bDepartment of Biophysics, Cardiovascular Research Institute Maastricht, Maastricht University, 6200 MD Maastricht, The Netherlands
cDepartment of Bioengineering, University of Washington, Seattle, WA, USA
frits.prinzen{at}fys.unimaas.nl
* Corresponding author. Tel.: +31-43-388-1200; fax: +31-43-388-4166
Several studies have shown that, per unit mass, myocardial blood flow (MBF) and oxygen consumption are similar in hypertrophic and non-hypertrophic ventricles. This observation may be explained by the degree of myocardial growth matching the increase in oxygen demand. Such matching may, however, not be perfect at the local level, because substantial heterogeneity of MBF exists within the ventricular wall. We investigated to what extent local growth and MBF are matched after redistribution of workload within the left ventricular (LV) wall. Redistribution of workload was established by ventricular pacing at physiological heart rate, which induces asynchronous activation and contraction. Local wall mass (2D-echocardiography) and MBF (fluorescent microspheres) were determined in the canine LV wall before (t=0) and after 6 months of normal sinus rhythm (SHAM group, n=5) or 6 months of pacing at the LV free wall (PACE group, n=8). During acute pacing MBF (ml/min/g) increased with increasing distance to the pacing site. Local relative MBF (rMBF, local MBF normalized to mean MBF in the LV wall) varied from 0.8 adjacent to the pacing site to 1.2 in remote regions. After 6 months of pacing these regional differences had disappeared, probably due to changes in wall mass, which increased with increasing distance to the pacing site (by up to 39±13%). In SHAM animals rMBF at t=0 correlated well with rMBF 6 months later (r=0.71). In PACE animals, however, this correlation was poor (r=0.33), because rMBF increased in regions close to the pacing site with initial rMBF<1 and rMBF decreased in regions remote from the pacing site with initial rMBF>1. Conclusions: After redistribution of workload within the LV wall as induced by ventricular pacing, local load-regulated growth tends to equalize MBF distribution, but local adaptation of MBF also depends on initial MBF.
KEYWORDS Hypertrophy; Regional blood flow; Ventricular function
* Supported by: The Bakken Research Center, Medtronic, Endepolsdomein 5, 6229 GW Maastricht, The Netherlands
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