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Early postoperative flow rates after internal thoracic artery grafting for the left coronary artery system
J Cremer1, W Harringer, G Hermann
1Division of Thoracic and Cardiovascular Surgery, Hannover Medical School, Germany.
Insights
Internal thoracic artery (ITA) grafts provide adequate blood flow for myocardial demands, even in critical coronary situations. Early postoperative flow rates in ITA grafts are sufficient, challenging previous limitations.
Area of Science:
- Cardiovascular Surgery
- Vascular Physiology
- Coronary Artery Bypass Grafting
Background:
- Internal thoracic artery (ITA) conduits are crucial for coronary artery bypass grafting (CABG).
- Concerns exist regarding the adequacy of ITA graft flow rates in high myocardial demand scenarios.
- This study investigates early postoperative flow characteristics of ITA grafts.
Purpose of the Study:
- To determine early postoperative flow rates and capacities of internal thoracic artery (ITA) grafts.
- To assess the impact of vasodilatory stimulation on ITA graft hemodynamics.
- To evaluate the suitability of ITA grafts for high myocardial demand.
Main Methods:
- Intravascular Doppler and quantitative angiography were used in 20 patients post-CABG.
- Flow rates, peak velocities, and diastolic-systolic velocity ratios were measured in ITA grafts (LAD and CX).
- Graft response to nitroglycerin and papaverine stimulation was assessed.
Main Results:
- Resting flow rates for ITA-LAD and ITA-CX grafts were comparable (51.0 +/- 34.2 ml/min and 44.7 +/- 16.4 ml/min, respectively).
- Both nitroglycerin and papaverine significantly increased flow velocities and diastolic-systolic ratios.
- Papaverine induced significant graft diameter dilatation, particularly in ITA-LAD conduits.
Conclusions:
- Functioning ITA grafts demonstrate adequate resting blood flow (50-60 ml/min) for myocardial supply.
- Increased flow is primarily achieved through enhanced flow velocity and diastolic proportion.
- Graft diameter augmentation, especially with papaverine, may further improve flow capacity.
Objective:
The low perioperative flow rates of internal thoracic artery (ITA) conduits have been regarded as a limitation of their use in critical coronary situations with a high myocardial blood demand. To clarify whether these restrictions are justified, early postoperative flow rates were determined.
Methods:
Following bilateral ITA grafting, 48 of 106 patients (April 1993-September 1994) underwent recatheterization. Subsequent to control angiography between days 8 and 12, 20 of these patients were studied by intravascular Doppler techniques applied for ITA grafts supplying the left anterior descending artery (LAD) and branches of the circumflex system (CX) (n = 20). Doppler spectral analysis allowed for determination of the average peak velocity and diastolic-systolic velocity ratio. Vascular diameters were assessed by simultaneously performed quantitative angiography and mean flow rates were calculated. All parameters were recorded at rest and following selective stimulation with nitroglycerin (0.2 mg) and papaverine (12.5 mg) to evaluate the graft flow capacity.
Results:
Baseline values of average peak velocity at rest were 24.6 +/- 11.5 cm/s for ITA-LAD conduits and 21.9 +/- 6.8 cm/s for ITA-CX pedicles. Following dilative stimulation with papaverine, a significant increase in average peak velocities were obtained for both locations (ITA-LAD: 47.3 +/- 17.1 cm/s, ITA-CX: 42.3 +/- 11.8 cm/s). The application of nitroglycerin had a similar effect (ITA-LAD: 42.6 +/- 15.3 cm/s, ITA-CX: 40.3 +/- 10.7 cm/s). The vascular diameters of ITA conduits remained unchanged on nitroglycerin stimulation, whereas papaverine effected significant dilatation in both locations. Flow rates at rest were not significantly different (ITA-LAD: 51.0 +/- 34.2 ml/min, ITA-CX: 44.7 +/- 16.4 ml/min) and maximal flow increase was observed following papaverine stimulation of the LAD conduits (116.1 +/- 90.6 ml/min). Dilative stimulation effected an increase in diastolic-systolic velocity ratios from average values at rest in a range between 34% and 41.7% for both groups and substances.
Conclusions:
The basic blood flow in functioning ITA grafts appears to be similar in conduits supplying the LAD and marginal branches. Flow rates between 50 and 60 ml/min at rest should meet myocardial demands, even in the LAD position. Increased flow rates were predominantly based on higher flow velocities with an increased diastolic flow proportion. Enlargement of the graft diameter may exert additional effects, at least following papaverine stimulation at a particular concentration.