Prediction of myocardial blood flow by DPTI and prediction of the adequacy of myocardial O2 supply by the DPTI/STTI ratio under maximal coronary dilation

Abstract

The DPTI/STTI ratio as an estimate of the myocardial 02 supply/demand ratio and the prediction of myocardial blood flow (MBF) by the diastolic pressure time index (DPTD and other indices have been examined in intact anesthetized dogs. We analyzed 89 steady states including maximal alterations of the variables determining DPTI and STI~I. Myocardial blood flow was directly measured in the coronary sinus with a differential pressure catheter. An experiments were carried out under maximal coronary dilation obtained by application of dipyridamol. Hemodynamics and MBF were varied by use of pressure loading, (3-stimulation and ~-blockade, hypo-and hypervolemia, electrical stimulation and hemodilution. Hemodynamic variations included clinically significant situations such as tachycardiac heart failure based on exhausted coronary vascular reserve and severe anemia. Parameters of sufficient myocardial 02 supply were coronary venous 02 saturation, precordial Ecg, hemodynamic evaluation of myocardial performance, result of autopsy and determination of the wet and dry weight ratio.All tested parameters show a poor correlation for prediction of MBF. Correlation coefficient for DPTI is r = 0.60. Using the primary data of Buckberg(1) we obtained similar results for the correlation of DPTI to subendocardial blood flow measured with microspheres (r = 0.65). The highest r (0.66) was found in our data for the difference between mean diastolic aortic pressure and mean left ventricular diastolic pressure without regard to diastolic duration. Therefore, in contrast to theoretical expectation, diastolic duration is not a practically important determinant of MBF. A number of DPTI/STrI ratios fell far below the critical values *) Supported by the Deutsche Forschungsgemeinschaft, SFB 89, Kardiologie, GSttingen. 811

Effect of vasopressin on phasic coronary blood flow

“…This result seems to be contradictory with the observed decrease in diastolic coronary flow induced by vasopressin. The more important increase in the DPTI than in SPTI did not take into account the change in the critical closing pressure and may explain the increase in D PTI/SPTI ratio (2,3,4,5). When a drug has a direct effect on the coronary circulation, the DPTI/SPTI ratio becomes a bad indicator of the oxygen demand-oxygen supply balance because of the role of the change in the critical closing pressure as a determinant of the coronary flow driving pressure (3,4).…”

Improvement in Coronary Flow Reserve Determined by Positron Emission Tomography After 6 Months of Cholesterol-Lowering Therapy in Patients With Early Stages of Coronary Atherosclerosis

“…With regard to noninvasive calculation of MCR, aortic perfusion pressure was not subtracted from diastolic left ventricular opposing pressure because the quantitative influence of the myocardial or extravascular component of resistance can largely be neglected when left ventricular function and end-diastolic pressures are within normal limits. 20 …”

A critical look at currently used indirect indices of myocardial oxygen consumption

“…The tension-time index is better called systolic pressure-time index (13), since it does not evaluate systolic wall tension due to neglect of ventricular dimensions. In the last years "TTI" won further importance as a predictor of MVO2 in connection with a diastolic pressure-time index (DPTD as a predictor of myocardial oxygen supply forming together the myocardial supply/demand ratio (DPTI/TTI) (23,24), which has been critically examined in recent works (25,26).…”