Cardiac Function and Peripheral Circulatory Adjustments in Patients with Acute Myocardial Infarction

Observations during the Early Stage of AMI

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Since little is known concerning the effect of different types of cardiac dysfunction on the peripheral circulation in acute myocardial infarction, cardiac and peripheral circulatory hemodynamics were measured simultaneously and sequentially in the Coronary Care Unit in 40 patients with acute myocardial infarction (AMI) using a Swan-Ganz catheter and venous occlusion plethysmography.
Patients were classified by clinical assessment (Killip) and into four hemodynamic subsets (HS) according to pulmonary capillary wedge pressure (PCWP) and cardiac index (CI) measures obtained by invasive central hemodynamic monitoring (Forrester): uncomplicated AMI, HS-I (PCWP≤18mmHg, CI>2.2L/min/m²) 15; pulmonary congestion, HS-II (PCWP>18mmHg, CI>2.2L/min/m²) 15; peripheral hypoperfusion, HS-III (PCWP≤18mmHg, CI≤2.2L/min/m²) 4; cardiogenic shock, HS-IV (PCWP>18mmHg, CI≤2.2L/min/m²) 6.
Measurements taken within 48 hours after the onset of AMI showed significantly lower calf blood flow (p<0.05) and calf venous capacitance (p<0.01) and higher calf vascular resistance (p<0.05) in all AMI classifications compared to 10 normal subjects.
In uncomplicated AMI group (Killip I and HS-I) calf blood flow and venous capacitance were significantly reduced while calf vascular resistance remained unchanged from normal. In AMI complicated by pulmonary congestion (Killip II and HS-II), in addition to reduced calf venous capacitance, calf blood flow was further significantly reduced (p<0.05) due, in part, to a rise in calf vascular resistance (p<0.05). In AMI complicated by severe heart failure and shock (Killip III, VI and HS-IV), mean changes in the periphery were not statistically different from those seen in patients with pulmonary congestion alone. In patients with AMI complicated by poor peripheral perfusion (HS-III), the peripheral changes did not show significant differences from those seen in uncomplicated AMI (HS-I).
Significant correlations were found between calf blood flow and PCWP (r=-0.37, p<0.05) and CVP (r=-0.31, p<0.05); calf vascular resistance and PCWP (r=+0.36, p<0.05) and systemic vascular resistance (r=+0.43, p<0.01).
Sequential daily peripheral hemodynamic changes in 14 H-I patients not requiring specific therapy showed that calf blood flow took 5 days, calf vascular resistance 3 days and calf venous capacitance 7 days to return to within normal levels.
Our results show that 1) resistance vessel constriction is greater with higher PCWP and CVP, 2) maximum constriction of capacitance vessels occurs even in the absence of forward or backward failure, and 3) the constriction of capacitance vessels is more prolonged than that of resistance vessels in uncomplicated AMI.