The Role of Collateral Circulation in Preserving Myocardial Function

Th e coronary collateral circulation is an alternative source of blood supply to the myocardium jeopardized by the failure of the original stenotic or occluded vessel to provide adequate blood fl ow to this region. One hundred coronary angiograms and left ventriculograms of patients with coronary artery disease from the Cardiology Department of University Clinics Centre in Sarajevo were reviewed. Th e role of collateral circulation in preserving myocardial function was assessed by comparing regional left ventricular contractility in  instances of total arterial occlusion and adequate colateral circulation with that in  instances of total arterial occlusion and inadequate collateral circulation. Among the group with adequate collaterals, regional left ventricular contraction was normal in , hypokinetic in  and akinetic or dyskinetic in only . Among the group with inadequate collaterals, regional contraction was normal in , hypokinetic in   and akinetic or dyskinetic in . Th ese data indicate that collateral circulation plays an important role in preserving myocardial contractility in patients with coronary artery disease.


Introduction
Th e normal human heart has been found to contain a profusion of small, anastomotic vessels classifi ed as "homocoronary"anastomoses if they connect segments of the same artery and "intercoronary" anastomoses if they connect branches of diff erent arteries.Althought the anastomoses can be identifi ed in autopsy specimens, they cannot be demonstrated angiographically when normal or only mildly impaired circulation is present because they carry only minimal fl ow and their small size is beyond the limits of resolution of presently available imaging systems for coronary arteriography.If obstruction of a major artery occurs, however, a transanastomotic pressure gradient is created in those anastomoses connecting the distal segment of the involved artery with either the proximal segment of the same artery or nearby segments of other arteries.Because of this gradient, an increased volume of blood is propelled through the anastomoses, which progressively dilate and eventually become visible angiographically as collateral channels (,) Th e collateral circulation has been studied in experimental animal models with certain limitations on their applicability to humans.Th e in vivo assessment of collateral function in humans developed from a qualitative anatomic evaluation by angiography to a physiological assessment by microsensors recording coronary fl ow velocity and pressure during cardiac catheterization.Most of these studied were done in selected patients with single vessel disease, nonocclusive lesions, and normal ventricular function (,,,).Little is known of the prominent role of collaterals in chronic total coronary occlusions.In chronic total occlusions, the collaterals are capable of complete preservation of myocardial function or of providing a minimum perfusion for hibernating myocardium.Both the extent of preserved regional function and the duration of the occlusion would be likely determinants of collateral function (,,,,,) Th e purpose of this study is to defi ne the specifi c pathways of the coronary collateral circulation, and second, to determinate the effect of this collateral circulation upon left myocardial function.

Material and Methods
Coronary angiograms and left ventriculograms of hundred patients with signifi cant coronary artery disease were analyzed.Coronary arteriography was performed by the percutaneous transfemoral approach originally described by Judkins.Serial radiographs of the coronary arteries were obtained in the right and left anterior oblique projections.For all patients we applied left ventriculography for the evaluation of its function, ejective fraction and kinetics.Left ventriculography was performed in the right anterior oblique projection.Th e eff ect of collaterals upon myocardial function was studied in  instances with occlusion of the left anterior descending artery (LAD) and right coronary (RC) artery.On the angiograms we analyzed collaterals as "good" (average calibar greater than , mm) and "bed" (average calibar mm and less).Based on value of ejection fraction (EF) we analyzed the role of collateral circulation in preserving of left myocardial function.Th e performance of the various regions of the left ventricle was evaluated by studyng contractility of the chamber as seen at ventriculography.Regional function was considered normal, if there was uniform, forceful and nearly concentric contraction of the endocardial surface.It was cosidered mildly impaired if hypokinsia was present, and severely impaired if akinesia or dyskinesia occurred.Regional contractility of the aff ected myocardial segments in the groups with adequate and inadequate collateral circulation was then compared.Th e investigations were done with respect to ethical standards regulated by Helsinki Declaration.

Results
Among the  angiograms with norrowing greater then  or complete occlusion of the coronary arteries, adequate collateral circulation was visualized in  instances (Figure  and ).We established equal number of instances with inadequate collateral circulation.Th e diff erent collateral pathways were noted in patients with right and left coronary obstruction.Homocoronary and intercoronary pathways, a network of very small and short channels is frequently seen bridging a localized obstruction of a major coronary artery. .Our results showed the diff erences in associated regional left ventricular function contractility into groups with adequate and inadequate collateral circulation.It was found that in the group with adequate collateral circulation ( instances), regional left ventricular function was normal in  cases (), mildly impaired, (hypokinetic) in  ().In only  instances () were akinesia or dyskinesia seen.(severely impaired).On the other hand, in the group with inadequate collateral circulation, normal regional contractility was present in only  (), and hypokinesia in ().Th e vast majority,  cases or , demonstrated akinesia or dyskinesia of the corresponding myocardial segment.Using Student-t-test the diff erences between the groups were signifi cant at the , level.In the group with adequate collaterals and good left ventricular function the values of ejective fraction (EF) was about , in the second one was about .

Discussion
Th is study indicates that collateral circulation plays a major role in preserving myocardial function in patients with coronary artery disease, a view which has been substantiated in material presented recently by several other groups.Invetigators (,,) found that contraction abnormalities were slightly more prevalent among the group with collaterals and concluded, therefore, that collateral circulation did not protect againist development of an abnormal left ventricular contraction pat-tern.Although the present study and recent work of other groups (,,,) have indicated that eff ective collateral circulation helps preserve myocardial function in patients withcoronary artery disease, several additional aspects may require further clarifi cation.First, it must be determined whether the existence of a well-developed collateral circulation can prevent future infarction or death.Authors (,) have investigated this point and concluded that it does not provide such protection.On the other hand (,) has stated that patients with adequate collateral circulation emanating from nonstenotic arteries have a significantly better prognosis than patients with poorly developed collaterals.A recent study by (,) has confi rmed that an improved long term prognosis is associated with good collateralization in patients with angiographically documented single and double vessel coronary disease.Th e surgical signifi cance of collateral circulation likewise has not yet been properly evaluated.On the one hand, by preserving both left ventricular contractility and patency of the distal segments of obstructed arteries, collateral circulation maintains conditions which are favorable for the construction of successful coronary bypass grafts.On the other hand, there may be cases in which the autorevascularization of collateral circulation is sufficient to obviate the necessity of surgical revascularization.

Conclusion
Collateral circulation was better in patients with coronary occlusion and normal regional function than in those with impaired regional function.Th e present study have indicated that eff ective collateral circulation helps preserve myocardial function in patients with coronary artery disease.Th e eff ective collaterals with diameter more than mm have importance role in protection of left ventricle function (EF-).On the other hand, collaterals with diameter less than mm can not preserve left ventricular function.(EF-).