DPTI/STTI--an index of the myocardial oxygen supply/demand ratio?

The DPTI/STTI (diastolic pressure-time index/tension-time index) ratio is applied as an indicator of myocardial ischemia particularly in cardiovascular and anesthesiologic care units. The validity of the DPTI/STTI ratio was examined in intact dogs with large variations of oxygen supply and demand. The correlation of DPTI/STTI to the directly measured oxygen supply/demand ratio was poor even under maximal coronary vasodilation. Many data points were far below the critical DPTI/STTI values (reported previously) without occurrence of myocardial ischemia, failure, or edema. Therefore caution is necessary if the DPTI/STTI ratio is to applied to humans.