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Published on: November 24, 2014
Studies of blood flow in aorta-to-coronary venous bypass grafts in man
Insights
This study measured vein graft flow in bypass patients, finding it stable post-procedure. Pharmacological agents like isoproterenol and nitroglycerin altered flow, impacting coronary vascular resistance.
Area of Science:
- Cardiovascular Surgery
- Vascular Physiology
- Pharmacology
Background:
- Coronary artery bypass grafting (CABG) is a critical procedure for treating coronary artery disease.
- Understanding hemodynamics and pharmacological responses in vein grafts is essential for optimizing patient outcomes.
- Previous studies have explored graft performance, but detailed pressure-flow dynamics and drug effects require further investigation.
Purpose of the Study:
- To characterize pressure-flow dynamics in aorta-to-coronary vein grafts during and after bypass surgery.
- To evaluate the impact of vasoactive agents (isoproterenol, norepinephrine, phenylephrine, nitroglycerin) on graft flow and coronary vascular resistance.
- To investigate correlations between graft flow and anatomical factors or ventricular function.
Main Methods:
- Conducted pressure-flow measurements in 57 patients undergoing single aorta-to-coronary bypass.
- Administered vasoactive drugs (isoproterenol, norepinephrine, phenylephrine, nitroglycerin) via intravenous infusion or direct graft injection.
- Analyzed flow contours, graft flow stability, flow debt repayment after occlusion, and changes in hemodynamic parameters (e.g., LV dp/dt, LVEDP).
Main Results:
- Vein graft flow stabilized approximately 30 minutes post-bypass (mean 35 cm³/min).
- No correlations found between graft flow and graft laterality, collaterals, block severity, or ventricular dyskinesis.
- Isoproterenol transiently increased graft flow; norepinephrine and phenylephrine affected vascular resistance differently; nitroglycerin reduced coronary vascular resistance and increased graft flow.
Conclusions:
- Vein graft flow is hemodynamically stable post-reperfusion, independent of certain anatomical and functional factors.
- Pharmacological agents significantly modulate vein graft flow and coronary vascular resistance, highlighting their potential therapeutic roles.
- These findings provide insights into the physiological behavior of vein grafts and their response to vasoactive interventions.
Abstract:
Pressure-flow measurements were obtained from the vein graft of 57 patients undergoing a single aorta-to-coronary bypass procedure. The flow contour was similar to phasic left coronary artery flow in dogs except for a transient increase during systole possibly related to elongation of the graft. Flow was highest during bypass and decreased to a stable value 30 min after bypass. In 42 patients, flow at this time was 35+/-2 cm(3)/min (mean+/-sem).NO CORRELATIONS WERE DEMONSTRATED BETWEEN FLOW AND THE FOLLOWING: left vs. right grafts, presence or absence of collaterals, total vs. partial block, or the presence or absence of ventricular dyskinesis. In 32 patients, no correlation between these anatomic findings and the presence of reactive hyperemia was demonstrated. In 17 patients, occlusion of the graft for 10 sec resulted in a mean 51.5% flow debt repayment. In nine patients, injection of 0.3 mug of isoproterenol into the graft increased flow from 45+/-6 to 69+/-9 cm(3)/min within 4-7 sec without changes in rate, pressure, time derivative of left ventricular pressure (LV dp/dt), or left ventricular end diastolic pressure (LVEDP). Maximum increases to 87+/-10 cm(3)/min occurred 12-20 sec after injection with concomitant changes in these parameters. Intravenous infusion of norepinephrine did not change vascular resistance, whereas phenylephrine did. In six patients, injection of 0.2 mug of norepinephrine into the graft decreased flow from 49+/-6 to 25+/-5 cm(3)/min within 5-8 sec. Intravenous infusion of 0.15 mg of nitroglycerin decreased coronary vascular resistance from 2.7+/-0.4 to 2.3+/-0.3 mm Hg/cm(3) per min. In five patients, 0.12 mg of nitroglycerin injected into the graft increased flow from 46+/-7 to 71+/-13 cm(3)/min and lasted 20-40 sec.
