Kones, Richard J.
May 1974
Angiology;May1974, Vol. 25 Issue 5, p317
Academic Journal
Altered LV performance in cardiogenic shock (CS) may be describe by considering 5 variables: preload, after load, contractility, heart rate, and synergy of contraction. In addition, two fundamental relations of importance are (i) the function cardiac output (CO) vs. preload—the length-tension or Starling curve—and (ii) CO vs. afterload—the force-velocity relation. Increases in the first four of the above variables and dysynergy are all associated with augmented myocardial oxygen (O2) consumption (MVO2), but to different extents. Hemodynamic patterns in CS are heterogeneous, but ↓ coronary blood flow (CBF), stroke volume and CO, ↑ myocardial O2 extraction (A-CSO2) and ↑ peripheral vascular resistance are relatively constant findings. LV compliance is reduced and hence LV end-diastolic pressure (LVKDP) may be elevated without other evidence of poor LV function. Such an augmented LV filling pressure in fact defends the CO via ‘Starling compensation.’ O2 available to the myocardium is given by the product of CBF and A-CSO2. A-CSO2 is in turn directly proportional to arterial O2 content. The difference in alveolar-arterial O2 tension is proportional to both LV mass infarcted and resultant elevation in LVEDP. In the coronary arterial bed, blood flow is negligible below the ‘critical closing pressure,’ increases rapidly as the pressure bead rises, then levels. Undue rises in mean arterial pressure are not matched by meaningful increases in CBF beyond a given value of arterial pressure. Survival of marginally viable myocardium in an ischemic zone depends upon the balance between O2 available and O2 demand. Maneuvers which inordinately increase intramyocardial tension, contractility or heart rate further the imbalance between (CBF × A-CSO2) and MVO2 and may result in further cell death. Hence although CO may be enhanced short-term during the therapy of CS, the O2 cost may extract an unacceptable metabolic price. The management of CS—medical and surgical—should be primarily directed al restoration of myocellular oxygenation and nutrition. To this end, unnecessary elevations in heart rate and contractility are to be avoided. The heart may be unloaded during diastole by intra-aortic balloon counterpulsation, a technique which also improves coronary blood flow. The use of other agents, such as glucose-insulin-potassium, corticosteroids, hyaluronidase, and the beta-blockers, are currently being investigated.


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