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Anatomy of the First Septal Perforating Artery: A Study with Implications for Ablation Therapy for Hypertrophic Cardiomyopathy
mandrp singh, MD; william D. edwards, MD; dav.d R. holmes, jr, MD;
A. jamil tajik, MD; AND rick A. nishimura, MD

• Objective: To determine the variability in the size and distribution of the first septal perforating-artery (FSPA).
« Material and Methods: In this pilot study, 10 fresh autopsy hearts from patients who did not have hypertrophic cardioniyopathy (HCM) or clinical evidence of coronary artery disease were evaluated for the variability in the size of the FSPA. The size of the FSPA was also measured during coronary angiography in 8 patients with HCM who were undergoing alcohol septal ablation.
• Results: Of the 10 autopsy hearts, 2 had a large FSPA (>1.0 mm in maximal diameter) with prominent septal myocardial distribution, 2 had a medium-sized FSPA (0.5-0.9 mm), 2 had a small FSPA (0.1-0.4 mm), 3 had a tiny FSPA (<0.1 mm), and I had an indiscernible ostium. In 2 patients the FSPA supplied (he right ventricular free wall. In 4 patients the basal ventricular septum was incompletely supplied by the FSPA. Of the 8 patients with HCM, the FSPA was larger than 2 mm in diameter in 2 patients, 1 to 2 mm in 4, and smaller than 1 mm in 2. The distance between the left anterior descending coronary artery ostiuni and the origin of the FSPA ranged between 13.1 and 37.4 mm, indicating a large variation in the size and distribution nl the FSPA.
• Conclusions: Variability in the size and distribution of the FSPA in patients without HCM was substantial. Areas of the heart other than the basal septum were supplied in some patients by the FSPA. In other patients the FSPA did not supply the entire basal septum. Similar findings were noted in patients with HCM. A detailed evaluation uf the distribution of the FSPA may be necessary in all patients with HCM who are undergoing alcohol septal ablation.

Patients with hypertrophic cardiomyopathy (HCM) can present with disabling symptoms of dyspnea, angina, or exertional syncope due in part to obstruction of the left ventricular outflow tract.1-3 Despite optimal medical therapy, some patients have persistent severe symptoms caused by outflow tract obstruction. Septal myeclomy has been considered the treatment of choice in these patients.4-6 As an alternative, dual-chamber pacing has been advocated, but only a small percentage of patients have a modest reduc­tion in gradient and sustained symptomatic improvement.7-9
Recently, catheter-based infarction of the ventricular septum supplied by the first septal perforating artery (FSPA) of the left anterior descending coronary artery was proposed as a nonsurgical method to treat patients with severely symptomatic HCM.10-13 Because the FSPA suplies the portion of the ventricular septum that contributes to subaortic stenosis in most patients with the obstructive form of MCM, knowledge of the size and distribution of this artery is important. The purpose of this pilot study was to determine the variability in the size and distribution of the FSPA. Initially, the distribution of the FSPA was stud­ied in 10 fresh autopsy hearts with use of an injection of barium sulfate and gelatin. Subsequenlly, the distribution of the FSPA was evaluated in 8 patients with HCM who were undergoing alcohol septal ablation.
MATERIAL AND METHODS
We studied 10 fresh autopsy hearts from patients who did not have HCM or clinical evidence of coronary artery disease. This study was approved by the Mayo Foundation Institutional Review Board. The ascending aorta was transected, and the left main coronary ostium was identified. Next, the left main and left anterior descending coro­nary arteries were opened longitudinally from above. The origin of the FSPA was the first discernible ostium in the left anterior descending coronary artery along its septal aspect. A solution of diluted barium sulfate and gelatin was manually injected into the ostium of the FSPA through a 26-gauge needle attached to a 10-mL syringe.14 Radio­graphs were taken in a right anterior oblique projection to delineate the size and distribution of the FSPA in the intact heart. Hearts were fixed in formalin for 24 hours. Short-axis ventricular sections, 1 cm thick, were. obtained, and radiographs of all slices were prepared to show the distribu­tion of the FSPA.
The distribution of the FSPA was then evaluated clini­cally in 8 consecutive patients with HCM who were undergoing alcohol septal ablation. In each of these patients, selective coronary angiography was performed by using a right anterior oblique view with cranial angulation to delin­eate the FSPA. A quantitative computer analysis program with automatic border detection was used to measure the following: (1) the mean diameter of the left anterior de­scending coronary artery proximal to the FSPA, (2) the distance from the ostium of the left anterior descending coronary artery to the FSPA, (3) the maximal diameter of the FSPA, (4) the distance from the FSPA to the second septal perforating artery, and (5) the maximal diameter of the second septal perforating artery.


Table 1, Variability in the Size and Distribution of the First Septal Perforating Artery
in 10 Autopsy Hearts*


*FSPA = first septal perforating artery; NA = not available.

RESULTS
Of the 10 autopsy hearts, 2 had a large FSPA (>1.0 mm in maximal diameter) with prominent seplal myocardial dis­tribution, 2 had a medium-sized FSPA (0.5-0.9 mm), 2 had a small FSPA (0.1 - 0.4 mm), 3 had a tiny FSPA (<0.1 mm), and 1 had an indiscernible ostium (Table 1, Figures I and 2). In the 7 hearts with arterial measurements, the diameter of the FSPA at its origin ranged from 0.05 to 1.8 mm (mean, 0.6 mm). Based on body weight and heart weight, FSPA diameters ranged from 0.0005 to 0.020 mm/g (mean, 0.009 mm/g) and 0.00012 to 0.004 mm/g (mean, 0.0016 mm/g), respectively.
In 2 patients, the FSPA also supplied the anterior wall of the right ventricle. In the 4 patients with an FSPA less than 0,1 mm in diameter, the basal septum was incompletely supplied by the FSPA.
Of the 8 patients with HCM, 2 palienis had an FSPA larger than 2.0 mm in diameter, 4 had an FSPA between 1.0 and 2.0 mm in diameter, and 2 had an FSPA smaller than 1.0 mm in diameter. In 2 patients, the first and the second seplal perforating arteries arose from a common ostium. The distance between the ostium of the left anterior de­scending coronary artery and the origin of the second per­forating artery varied between 13.1 and 37.4 mm, indicat­ing a large variation in the length of the septum supplied by the FSPA (Table 2, Figure 3).
DISCUSSION
The pathophysiology of HCM is complex and includes abnormalities of rhythm, diastolic function, and systolic function.2,3 In a subset of patients, symptoms are due to a dynamic left ventricular outflow tract obstruction from a hypertrophic septum and systolic anterior motion of the mitral valve. Therapy for patients with severe obstruction has been directed at reducing the obstruction of the dynamic left ventricular outflow tract. 2,4,7 Surgical myotomy or myectomy alleviates symptoms in more than 90% of patients.4-6
In most people the FSPA supplies the basal portion of the ventricular septum. Investigators have reported the use of catheter-based alcohol-induced thrombosis of the FSPA 111 the treatment of the patients with HCM.10-13 Sigwart10 found that transient occlusion of the FSPA caused akinesis of the basal ventricular septum and reduction in the outflow gra­dient. With use of a catheter-based technique, alcohol was instilled into the FSPA, creating an arterial occlusion and an infarct of the basal ventricular septum. This resulted in a lowering of the degree of outflow tract obstruction and a reduction in symptoms. A postinfarction remodeling effect also occurs to the point that the size of the outflow tract increases with time after successful ablation.
Although an increasing number of patients are rcceiving catheter-based septal ablalion, the long-term outcome is unknown, and the ultimate role of this procedure is not defined.10-12,15,16 Our findings indicate that the FSPA varies widely in size and distribution from patient to patient. It is important to understand the distribution and variation of the FSPA when septal ablation is being performed. Some patients had an FSPA that perfused only a smoll portion basal septum, whereas in others it not only perfused the septum but also perfused the entire right ventricular wall. Thus, occlusion of the FSPA may have a minimal effect in one patient but may cause transmural infarction, right ventricular infarction, or septal rupture in another patienl. This wide variation in the size and takeoff was also seen in patients with HCM. Our findings are consistent with the clinical observation that other seplal perforators may be necessary for ablation, depending on the size of the FSPA and the site of obstruction.
The current pilot study found a substantial variability in the size, distribution, and perfusion regions of the FSPA in patients without HCM. A large variation in the size and takeoff of the FSPA was also identified in patients with HCM. These findings indicate that successful septal ablation may not be possible in all patients if only the FSPA is injected. Also, alcohol injection into the FSPA has the potential to create large infarctions of the septum and right ventricle. Meticulous evaluation of the distribution and perfusion of the septal arteries before ablation may be necessary for optimal patient care.

Figure 1. Postmortem radiographs of a heart with a large first septai perforating artery. Left, Intact heart has a prominent branching artery (right anterior oblique view). Right, Ventricular slices show extensive distribution within the basal septum (short-axis view).
Figure 2. Postmortem radiographs of a heart with a diminutive first septal perforating artery. Left, Intact heart has a small arterial twig (right anterior oblique view). Right, Ventricular slices show mini­mal distribution within the basal septum (short-axis view).

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