DPTI-STTI RATIO AS AN ESTIMATE OF THE MYOCARDIAL OXYGEN SUPPLY-DEMAND RATIO

The DPTI/STTI ratio is applied to man, both in health and disease, for estimating the myocardial oxygen supply/demand ratio. The physiological concept and the divergent values reported for the critical DPTI/STTI ratio led the authors to examine this index under maximal variations of oxygen supply and demand. 247 steady states in 15 intact dogs with patent coronary arteries, including 89 points at maximal coronary vasodilatation were analyzed. Coronary blood flow was measured directly. Oxygen supply and demand were varied by use of an intra-aortic balloon catheter, hypo- and hypervolemia, inotropic stimulation, beta adrenergic blockade, cardiac pacing, hemodilution and Persantin® (dipyridamol). Adequate myocardial oxygen supply was evaluated by precordial ECG and cardiac performance. The authors' studies demonstrated that DPTI bears only a poor relationship to myocardial blood flow at maximal coronary vasodilation (r=0.60). The result for the STTI as an estimate of myocardial oxygen demand is even poorer (r=0.53). A number of their values were far below the reported critical DPTI/STTI ratios without occurrence of subendocardial ischemia, depressed cardiac function or myocardial edema. Therefore, great caution is necessary if the DPTI/STTI ratio is applied in the treatment of patients with heart disease.