Significance of early angiographic follow-up after internal thoracic artery anastomosis in coronary surgery

Internal thoracic artery: anatomical and biological characteristics revisited

The left internal thoracic artery has become the conduit of choice for coronary artery bypass grafting, due to its superior patency rates at 10 or more years with little or no evidence of atherosclerotic changes. Recent evidence indicates that a second internal thoracic artery graft provides improved results relative to overall survival and major cardiac and cerebrovascular event-free survival, and reduces the need for repeat revascularization. However, the routine use of bilateral internal thoracic arteries is limited due to a perceived higher incidence of deep sternal wound infection. The surgical anatomy, collateral blood supply to the sternum, and biological characteristics of internal thoracic artery conduits are reviewed.

The alternative supply of the pectoralis major flap based medially in cases with previous surgical use of the internal thoracic artery: an anatomical study

In the present study we analyzed the anatomical basis for the use of the pectoralis major muscle based on alternative pedicles in order to evaluate its clinical applications in cases of potential lesion of the internal thoracic artery. The patterns of blood supply depending on the internal thoracic artery, previously dissected for coronary by-pass surgery, were studied in both sides of five embalmed cadavers and five anterior thoracic walls taken from autopsies. The secondary vascular pedicles depending on the internal thoracic artery for the pectoralis major muscle were dissected and injected with physiological saline stained solution in the embalmed cadavers. Moreover, studies of intravascular injection by means of radio-opaque contrast and physiological saline stained solution were carried out in the anterior thoracic walls obtained from clinical autopsies. The results showed that complete injection of the pectoralis major muscle was achieved depending exclusively on the two proximal perforating branches of the two first intercostal spaces, which represented the vascular pedicle for medial transposition of the pectoralis major flap, in cases with previous dissection of the internal thoracic artery for coronary by-pass.

Patent side branches do not affect coronary blood flow in internal thoracic artery-left anterior descending anastomosis: an experimental study

BACKGROUND

It has been reported that large side branches of internal thoracic artery grafts may steal flow from the coronary circulation. Material an.

METHODS

To assess the importance of the side branches, we measured the proximal and distal flow and pressures (mean subclavian artery pressure and mean arterial anastomotic pressure) at baseline and during infusion of adenosine (0.5 mg/kg/min) in 10 Landrace pigs in which an internal thoracic artery-left anterior descending anastomosis was constructed without interruption of the side branches. The difference between proximal and distal flow was considered to represent the blood flow of the internal thoracic artery side branches. Measurements were then repeated after surgical occlusion of all the side branches.

RESULTS

At baseline, blood flow of the side branches represented 18% of the total flow in the proximal internal thoracic artery, and this percentage remained constant under the infusion of adenosine, which caused a 220% increase of the cardiac index and a 368% increase of the proximal flow. The infusion reduced the gradient along the left internal thoracic artery (mean subclavian artery pressure-mean arterial anastomotic pressure) from 15 to 10 mm Hg (P =.02) as the result of a lower mean subclavian artery pressure, although the mean arterial anastomotic pressure remained constant. Interruption of all the side branches resulted in a small and not significant increase in distal flow even after adenosine infusion.

CONCLUSION

These observations suggest that blood flow in the side branches is minimal either at baseline and under combined systemic and coronary vasodilation. Clinically significant flow steal from the coronary circulation to the internal thoracic artery side branches seems then unlikely.

Steal phenomenon from mammary side branches: when does it occur?

BACKGROUND

The hemodynamic significance of patent mammary graft side branches is still controversial. This study was designed to evaluate the potential for flow steal of patent mammary side branches in different hemodynamic conditions.

METHODS

Echo-Doppler measurement of mammary graft flow was performed at rest and after dipyridamole-induced coronary vasodilatation in 10 patients with angiographic demonstration of evident mammary graft side branches (study group) and in 10 matched control patients (control group). Concomitant thallium-201 myocardial scintigraphy was performed to assess the adequacy of mammary flow to the myocardial oxygen demand. Patients of the study group were also submitted to flow evaluation in condition of selective muscular or combined systemic and coronary relaxation.

RESULTS

No difference in mammary flow and adequacy to myocardial oxygen demand was detected between patients of the study and control groups both at rest and after dipyridamole infusion. In patients with patent side branches the systolic-to-diastolic flow ratio was maintained in case of combined coronary and peripheral vasodilatation, whereas selective muscular relaxation led to an increase in the systolic and a reduction in the diastolic flow.

CONCLUSIONS

Flow steal from patent mammary graft side branches is possible only in case of selective muscular vasodilatation. As this situation is unlikely to occur in the clinical setting, the potential for flow steal of mammary side branches in cardiac surgery patients seems to be minimal.

Persistence of mammary artery branches and blood supply to the left anterior descending artery

BACKGROUND

Partial harvesting of the left internal mammary artery (LIMA) is a widespread technique used during minimally invasive coronary operations performed through a left anterior small thoracotomy. The influence of persisting LIMA branches was investigated to evaluate their effect on the blood flow of the left anterior descending artery.

METHODS

Thirty patients, 15 with totally (group A) and 15 with partially (group B) harvested LIMAs, were evaluated. All the patients underwent postoperative angiography, during which a flow map of the LIMA was performed. The average peak velocity and the diastolic-to-systolic peak velocity ratio were recorded. The LIMA graft flow pattern was recorded in the proximal and distal thirds of the artery. Intramammary adenosine (12 to 14 microg) was injected and the average peak velocities before and after injection were calculated.

RESULTS

The average peak velocity was similar in both groups in the proximal and distal thirds of the LIMA (25 +/- 7 and 26 +/- 5 cm/sec, respectively, in group A versus 27 +/- 5 and 25 +/- 5 cm/sec, respectively in group B; p = NS). The diastolic-to-systolic peak velocity ratio was similar proximally (0.78 +/- 0.3 in group A versus 0.69 +/- 0.3 cm/s in group B; p = NS), but not distally (1.72 +/- 0.1 in group A versus 0.97 +/- 0.3 in group B; p < 0.0005). The LIMA graft flow reserve was similar both proximally and distally (2.6 +/- 0.6 and 2.5 +/- 0.3 cm/s, respectively, in group A versus 2.6 +/- 0.5 and 2.6 +/- 0.3 cm/s, respectively, in group B; p = NS).

CONCLUSIONS

The persistence of LIMA branches does not influence the blood flow of the left anterior descending artery after acute adenosine-induced myocardial hyperemia. If a left anterior small thoracotomy is used in left anterior descending artery direct revascularization, complete LIMA harvesting is not mandatory and depends on the personal preference of the surgeon.

Microcoil embolization of large intercostal branches of internal mammary artery grafts

Coronary artery steal via a large unligated intercoastal side-branch of the internal mammary artery graft has been previously described in two case reports. We report a series of 7 patients with post-operative angina in whom microcoil embolization of such branch was performed. In 5 patients in whom complete occlusion of the branch was achieved, anginal symptoms were relieved; in contrast the 2 patients with persistent flow through the intercostal branch remained symptomatic despite all their grafts being widely patent. We conclude that large unligated intercostal branches of the IMA graft may be related with post-operative angina and their embolization is a simple, safe, and effective procedure.

Effects of internal mammary artery dissection on phrenic nerve perfusion and function

The effects of left internal mammary artery (LIMA) dissection and distal division on phrenic nerve perfusion and function were examined in an adult swine model. Phrenic nerve perfusion was determined by left atrial injection of radioactively labeled microspheres. Phrenic nerve function was determined by measuring nerve and diaphragm potentials evoked by bilateral phrenic nerve stimulation. In the first group of animals (n = 9), the LIMA was dissected with ligation of all its branches. Left phrenic nerve perfusion and function decreased after LIMA dissection in every animal studied, whereas only minimal changes were observed on the right. Sixty minutes after LIMA dissection, left phrenic nerve mean perfusion decreased 71%. Left phrenic nerve and left diaphragm mean action potential amplitudes decreased 54% and 80%, respectively. In the second group of animals (n = 4), the LIMA dissection was performed without division of the pericardiacophrenic artery, a small proximal branch of the internal mammary artery that supplies the phrenic nerve. Sixty minutes after LIMA dissection, left phrenic nerve perfusion had decreased by 21% from control values, with a corresponding decrease in left phrenic nerve and diaphragm mean action potential amplitudes of 19% and 23%, respectively. These results indicate that LIMA dissection with division of all its branches in this model is associated with a significant impairment in left phrenic nerve perfusion and function and suggests a causal relationship. These results may also explain the apparent increased phrenic nerve cold sensitivity and increased incidence of phrenic nerve dysfunction associated with LIMA grafting.(ABSTRACT TRUNCATED AT 250 WORDS)

Steal phenomenon caused by a parallel branch of the internal mammary artery

We report on a patient with postoperative mammary artery steal resulting from a parallel branch of the vessel as well as from a patent first left intercostal artery, both of which had not been divided. The patient was cured of angina pectoris after embolization of both vessels.