Septal perforator arteries: From angiographic-morphologic characteristics to related revascularization options

EDITORIALS

Septal perforator arteries: From angiographic-morphologic characteristics related revascularization options On Topaz, MD,a German0 St. Paul, Minn.,

DiSciascio,

and Richmond,

MD,b and George W. Vetrovec, MDb

Vu.

The interventricular septum, a structure that plays an essential role in left and right ventricular function,l contains important elements of the conduction system and is considered the most densely vascularized area of the heart.2 Significant obstructions of the septal arteries can cause ischemia, arrhythmias, angina, depression of ventricular function, and jeopardy of a large mass of myocardium.3 As septal arteries differ from the major epicardial coronary arteries in their size and intramural course, a direct surgical bypass of a diseased septal artery is rarely considered a realistic means of revascularization. The purpose of this communication is to delineate the unique morphologic characteristics and angiographic features of the septal perforator arteries and to discuss emerging options for their revascularization. Anatomy and morphology Anterior septal perforator

arteries. The anterior septal arteries are tributaries of the left anterior descending artery, supplying two thirds of the upper portion of the interventricular septum and perfusing almost the entire inferior third of the septum. Varying in number (usually from 4 to 13) with an average of eight branches,4 these vessels arise at a right angle to the epicardium, penetrate perpendicularly into the septal tissue, and traverse caudally in the septum from its anterior toward its posterior portion. Septal branches arising from the proximal segments of the left anterior descending artery are of greater caliber and length, move little during arteriography, and as a result are angiographically better demonstrated (in From Qwdiac Catheterization Laboratories of the St. Paul-Ramsey ical Center, University of Minnesota Medical School; and “the Medical lege of Virginia, Virginia Commonwealth University Received

for publication

Jan.

20, 1992;

accepted

March

MedCol-

2, 1992.

Reprint requests: On Topaz, MD, Cardiac Catheterization Laboratories, Section of Cardiology, St. Paul-Ramsey Medical Center, 640 Jackson St., St. Paul, MN 55101. 4/l/39275

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the right anterior oblique view) than are the distal septal branches, which are usually short and infrequently arborize.5 These unique characteristics are also helpful in angiographically distinguishing the proximal septal vessels from the diagonal and marginal arteries. The first anterior septal branch is usually the largest and longest (4 to 6 cm) and provides the most important collateral channels2 among all the septal arteries. This branch supplies a large portion of the septum as well as the bundle of His and the bundle branches of the conduction system. In many cases it also provides blood supply to the atrioventricular node. In some patients it supplies the anterior papillary muscle (Lancisi’s muscle) of the tricuspid valve as well. For the angiographer and the cardiovascular surgeon this septal vessel serves as a landmark for transition from the proximal to the middle segment of the left anterior descending artery, and the location of atherosclerotic lesions at the left anterior descending artery is described in relation to this artery. Anatomically there are several variations of anterior septal arteries4: 30% of normal angiograms demonstrate a large (1.5 mm in diameter or larger) first septal artery distally arborizing into at least four branches ramifying throughout the septum. In contradistinction, 28 % of normal coronary arteriograms show a small first septal artery. A further 24PG of normal coronary angiograms demonstrate two or three major proximal septal arteries, all of which are comparable in size, while in 18% there are multiple, small septal arteries. An unusually large, single septal artery is rarely encountered6 traversing deeper than and parallel to the left anterior descending artery, giving rise to the rest of the septal arteries, which then supply the proximal and middle portions of the septum. In cases of significantly diseased major epicardial arteries7,s the anterior septal arteries support the

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circulation by serving as anastomoses to posterior septal branches of the posterior descending artery. At times they can also act as bridge collaterals, communicating proximal septal branches to distal septal branches across a total occlusion of the left anterior descending artery. Specific attention to the angiographic appearance of certain morphologic features of the anterior septal arteries can be clinically useful. Compression on the anterior septal perforator arteries has been proposed as a marker of idiopathic hypertrophic subaortic stenosis.Y Kostis et all” reported that systolic obliteration and disappearance of the anterior septal branches with diastolic reappearance can also occur in aortic stenosis, severe proximal stenosis of the left anterior descending artery, and in association with myocardial bridges. The mechanism has been attributed to compression of the septal arteries by the myocardium through which they travel. Recent physiologic studies” indicate that such a compression may result in a retrograde flow in the proximal septal arteries, even under normal physiologic conditions. Detection of the anterior septal arteries’ angiographic pattern of motion can also be helpful in distinguishing patients with constrictive pericarditis from those with restrictive cardiomyopathy. Utilizing t.he cranial left anterior oblique angulation, Soto et aLI2 measured the maximal displacement between the most prominent anterior septal artery and the left anterior descending artery during diastole and systole. They found that the displacement of the anterior septal artery is abnormally exaggerated in patients with constrictive pericarditis compared with patients with restrictive cardiomyopathy and compared with normal populations. Soto et a1.12 attributed this phenomenon to the fact that in constrictive pericarditis the interventricular septum is not involved in the constrictive process, thus the septum acts in abnormal displacement to compensate for the limitation in diastolic ventricular filling. In contradistinction, the septal movement in restrictive cardiomyopathy is restricted as a result of septal tissue involvement in the primary disease. Posterior septal perforator arteries. The posterior septal perforator arteries are relatively short branches, seldom more than 15 mm in length,13 with a small caliber (1 mm on average). These branches arise at a right angle from the posterior interventricular descending branch of the right coronary artery. They vary in number from 6 to 20 and supply the posterior-superior third of the interventricular septum. These vessels are useful in angiographically distinguishing (in the right anterior oblique view) the posterior descending artery from acute marginal

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branches of the right coronary artery and distal branches of the left coronary artery.14 James and Burch13 proposed that the ultimate value of these posteriorly penetrating branches may be as a source of potential collateral circulation. In patients with a dominant circumflex artery, the posterior septal branches are derived from the posterior descending branch of the circumflex artery; thus the entire interventricular septum is solely perfused by the left coronary system. In such patients concomitant occlusions of the anterior descending and circumflex arteries often deprive the septum of nearly all effective circulation. Anomalous septal perforator arteries. An anomalous septal artery may arise directly from the aorta15 or originate from the left main, the first diagonal, the first obtuse marginal, or the circumflex artery.14 In addition, a septal artery may originate from the right aortic sinus or from the very proximal portion of the right coronary artery, l6 traverse the crista supraventricularis, ascend into the superior interventricular septum and then descend toward its distal portion. Such an anomalous septal branch can become important in patients with severe obstructive disease of the major coronary arteries by serving as an essential source of collateral circulation to proximal and distal segments of obstructed vessels, resulting in certain preservation of left ventricular function.17, l8 The incidence of anomalous septal perforator arteries varies considerably among angiographic reports. Bream et al.lg reported an incidence as high as 2.25 7; , while Rath et a1.17 reported an incidence of only 0.5%. Clearly, an anomalous septal artery can easily be missed if not specifically sought. Rarely, a normally arising septal perforator artery serves as a source for an anomalous coronary artery. Meyers et a1.20 described a patient with a single coronary ostium and a right coronary artery arising as a branch of the first septal perforator; the right coronary artery coursed through the interventricular septum before reaching the right atrioventricular groove. Erichetti et al. 21 described a patient with anomalous origin of the posterior descending artery from the first septal perforator. The left anterior descending artery was a short tapering vessel and the posterior descending artery coursed along the posterior interventricular sulcus to the left ventricular apex. In such an anomaly a proximal stenosis of the left anterior descending artery could not only result in anterior-septal wall ischemia and infarction, but also in inferior-posterior wall damage. Pathologic findings and clinical manifestations of diseased septal arteries. Pathologic22 and clinical23

studies have shown that coronary artery disease is

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frequent in the proximal portion of the major epicardial coronary vessels, with a progressive decrease in distal segments. Similarly, coronary atherosclerosis has a strong predilection for narrowing the ostium or the proximal portion of the large septal arteries. Pathologically and angiographically lesions are virtually absent from the distal portion of any septal artery. We suggest that forces caused by turbulent flow at the origin of the septal arteries, combined with the pressure of the interventricular septal tissue on its intramural vessels, are responsible for the concentration of atherosclerotic lesions at the proximal segment of the septal arteries. Significantly obstructive lesions of the septal arteries can lead to the development of chest pain, septal ischemia, and conduction disturbances including bundle branch block and complete heart block.3* l3 Ischemia resulting in septal tissue infarction may be clinically manifested by depression of right ventricular function and right, ventricular failure or by impairment of the function of both ventric1es.l Interventricular septal necrosis can be accompanied by rupture, a clinically catastrophic complication.“” Options for revascularization of the septal arteries Surgery. The unique anatomic characteristics of

the septal arteries render their surgical revascularization technically challenging and as a result this is rarely attempted. The penetrating course and the relatively small size of these vessels account for certain surgical difficulties. Among patients with atherosclerotic disease of the first (large) septal perforator, less than 305 have a vessel of sufficient size to receive a bypass graft. Since surgical exposure of this artery involves more dissection than is required for bypass of a major epicardial artery, there is increased probability of injury to the left anterior descending artery and its adjacent tributaries. Special care during bypass of septal arteries is needed to protect the right ventricular wall, since the first septal perforator often courses close to the right ventricular endocardium. The most feared complication of bypass grafting of the first septal artery is a rupture of the right ventricular wall. 25 Leakage at the anastomotic site also presents a challenging management problem, as it is difficult to apply sutures to the anastomotic site after cardiopulmonary bypass has been concluded.2” Indirect surgical revascularization of the first septal perforator can be performed by either bypass grafting or endarterectomy of the left anterior descending artery. Palomo et a1.15proposed that an anomalous septal artery could be bypassed more easily than a normally arising septal artery as the initial course of the anomolous artery may well be epicardial.

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Angioplasty. Considering the significant technical difficulties involving a surgical approach to diseased septal arteries, coronary angioplasty emerges as a reasonable mode for revascularization. We26 recently reported a series of 11 patients who underwent angioplasty of the anterior septal arteries. Seven patients had angioplasty of the first septal artery, three patients underwent dilatation of a second septal perforator, and another patient had angioplasty of the fourth septal artery. In each casethe nondiseased lumen of the septal artery was at least 2 mm in diameter. In seven, angioplasty was initially applied to a major epicardial vessel and angioplasty of the septal artery was performed to complete revascularization. Complications occurred in one patient only who developed acute closure of the septal artery following a successful dilatation. The situation was successfully managed by a repeat balloon inflation. All lesions were successfully dilated and the patients improved clinically. Four of these patients underwent repeat coronary arteriography for recurrence of chest pain a mean of 5 months after t,he initial angioplasty. In three (27 “; ) patients the septal perforator artery exhibited restenosis and was redilated successfully. A review of the literatureZ7-“* reveals at least five additional casesof successful angioplasty of a septal perforator art.ery. To judge from these cumulative results, the overall successrate of septal perforator angioplasty is similar to that for the major epicardial coronary arteries, and the complication rate does not exceed that of the latter group. We recommend angioplasty of the septal arteries in the following situations: (I) In patients with severely depressed left ventricular function whose symptoms are attributed to major coronary obstructions as well as to septal artery disease. These patients are poor candidates for coronary bypass surgery, and an infarction of the septum may further reduce their ventricular function; conversely, reduction of septal ischemia may benefit left, and right ventricular function. (2) In patients undergoing bypass grafting but presenting with angina related to septal artery disease (Fig. l), thereby facing a risk of septal ischemia and infarction resulting in reduction of right and left ventricular function. (3) In patients with an isolated, significant stenosis of a major septal artery with symptoms related to ischemia, cardiac dysfunction, or impaired conduction (Fig. 2). (4) In patients having concomitant significant narrowing of the septal artery and the left anterior descending artery. In such cases septal angioplasty can be performed as an adjunct to angioplasty of the epicardial artery. It should be emphasized that the septal branches are accessible for angioplasty provided the equip-

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Fig. 1. A, A Patient status post coronary artery bypasssurgery (CABGS) with significant angina attributed to a 99“0 proximal tubular stenosis(arrow) of a large septal perforator artery that provides collaterals

to the distal right coronary artery (RCA). The left anterior descendingartery (LAD) is totally occludedafter the origin of the septal artery. Cranial left anterior oblique projection. B, An LPS 2.0 (USC1 Division of C. R. Bard, Billerica, Mass.) balloon inflated. Caudal right anterior oblique projection. C, Final angiogram revealing (arrow) 25 5%residual narrowing. Left anterior oblique projection.

ment is carefully selected. Either steerable or flexible-steerable wires can be used to cross the stenotic lesions. Difficulties in traversing a severe ostial or proximal narrowing can be managed by accentuation of the J tip of the guide wire and utilization of more rigid, steerable wires. Deep engagement of the guiding catheter and advancement of the balloon catheter toward the septal artery can facilitate the passage of the guiding wire into the septal perforator artery. An over-the-wire balloon system, as well as a standard balloon catheter can be successfully applied. We3i have found ultralow profile balloon over-thewire catheter systems especially useful, as they maintain adequate lumen-wire fit and the necessary conformation for the curvature of the septal anatomy. Conclusions. A significant obstruction of a major septal artery can result in severe clinical manifestations including angina, infarction of the interventric-

ular septum, conduction abnormalities, and impairment of function of both ventricles. Because of their unique anatomic characteristics, these vessels are usually inaccessible to coronary bypass surgery. It is suggested that if medical treatment fails to treat clinical manifestations attributed to septal artery disease, then angioplasty of those vessels should be considered. Angioplasty can be applied to the involved septal vessel alone or as an adjunct to angioplasty of the left anterior descending artery. Based on a limited, initial experience, it appears that the overall successand the complication rate of septal artery angioplasty is similar to that of the major coronary arteries. In summary, the septal perforator arteries provide blood supply to the interventricular septum, which is considered the most densely vascularized area of the heart and a structure whose integrity is essential for

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Fig. 2. A, A patient with severe angina caused by single-vessel coronary artery disease; view demonstrates 90°; stenosis of the proximal first septal perforator (arrow). Left anterior oblique projection. 6, An 0.014 inch steerable wire (USCI) across the lesion. C, Balloon inflated to 7 atm (25 to 20 LPS, USCI). D, The balloon is fully expanded in a caudal right anterior oblique projection. E, Final angiographic results: no residual stenosis (arrow). Left anterior oblique projection. F, Final results (arrow) in right anterior oblique projection.

left and right ventricular function. Atherosclerotic coronary artery disease of the septal arteries can cause ischemia, arrhythmias, angina, as well as decrease the ventricular function and endanger a large

portion of the myocardium. Septal arteries differ from major coronary arteries in their size, intramural route, and pattern of distal ramification. Certain anatomic characteristics render bypass surgery of

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diseased septal arteries technically challenging, and as a result the technique is rarely applied. Recently, septal artery angioplasty has emerged as a promising means of revascularization. Based on a limited, initial experience, the overall success and complication rate of septal artery angioplasty is similar to that of major epicardial coronary arteries. This communication describes the morphologic characteristic of the septal perforator arteries and their influence on revascularization options and delineates indications and technical aspects of angioplasty of these vessels. We thank Laurie Topaz, Robin Appleton, and Shirley Crawford for their invaluable assistance in the preparation of the manuscript. REFERENCES

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