The effects of increased heart rate upon the physical and metabolic determinants of coronary blood flow in coronary heart disease provide a physiologic basis for the use of this investigative tool in cardiovascular studies. Heart rate increased by electrical pacing has minimal effects upon other hemodynamic indexes and arterial substrate concentrations, thus providing a considerable advantage over exercise and isoproterenol as a relatively uncomplicated myocardial stress. Atrial pacing represents a significant myocardial stress. Pressure-time per minute (PTM) increases with a nearly linear increase in myocardial oxygen consumption (MV̇O2). This probably represents a balance between 2 unmeasured determinants of myocardial oxygen consumption, left ventricular size and contractility. If left ventricular failure supervenes, MV̇O2/PTM may rise rapidly. Although total coronary blood flow increases in a manner adequate to meet oxygen demand even in coronary heart disease, the presence of regional lactate production implies that this vasodilating capacity is exceeded in some areas or depths of the coronary vascular bed.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine