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(Circulation. 1998;98:377-378.)
© 1998 American Heart Association, Inc.

Correspondence

Clinical Significance of Obstruction of the First Major Septal Branch

Mareomi Hamada, MD; Koji Kodama, MD; ; Kunio Hiwada, MD

The Second Department of Internal Medicine, Ehime University School of Medicine, Ehime, Japan

To the Editor:

The first major septal branch of the left anterior descending coronary artery seems to be closely related to disorder of the conduction system. Blood supply to the anterosuperior fascicle of the left bundle branch originates exclusively from the septal branches.¹ During myocardial ischemic attack due to stenosis of the proximal left anterior descending coronary artery, from the ostium of the left coronary artery to just before the first major septal branch, left-axis deviation often appears.^{2 3 4} Very recently, we reported⁵ that transient leftward QRS-axis shift during treadmill exercise testing or PTCA was a highly specific marker of proximal left anterior descending coronary artery disease. However, no one has confirmed that this left-axis deviation associated with myocardial ischemia is due to ischemia of the first septal branch.

Recently, Knight et al⁶ reported that nonsurgical septal reduction due to selective intracoronary alcohol injection into the first major septal branch reduced left ventricular outflow tract obstruction and improved symptoms in patients with hypertrophic obstructive cardiomyopathy. They also reported the ECG changes associated with this procedure. The most common ECG change was the development of right bundle-branch block (11 of 13 patients). Right bundle-branch block was accompanied by anterior ST-segment elevation in 3 patients and by the development of anterior Q waves in another 2. Two patients developed ventricular arrhythmias and 4 experienced transient complete heart block after injection of alcohol. We are very interested in the occurrence of right bundle-branch block and transient complete heart block.

The procedure performed by Knight et al provides an ideal opportunity to confirm the influence of the first septal branch on the ECG. Thus, we would like to ask Knight et al whether or not left-axis deviation occurred during the administration of alcohol into the first septal branch, and if it occurred, did left-axis deviation continue or not. In addition, we would like to ask why right bundle-branch block occurs during obstruction of the first septal branch of the left anterior descending artery.

View larger version (137K): [in this window] [in a new window]   Figure 1.

References

1. Milliken JA. Isolated and complicated left anterior fascicular block: a review of suggested electrocardiographic criteria. J Electrocardiol. 1983;16:199–211.[Medline] [Order article via Infotrieve]

2. Kulbertus HE, Humblet L. Transient hemiblock: an abnormal type of response to the Master two-step test. Am Heart J. 1972;83:574–576.[Medline] [Order article via Infotrieve]

3. Boran KJ, Oliveros RA, Boucher CA, Beckmann CH, Seaworth JF. Ischemia-associated intraventricular conduction disturbances during exercise testing as a predictor of proximal left anterior descending coronary artery disease. Am J Cardiol. 1983;51:1098–1102.[Medline] [Order article via Infotrieve]

4. Hamada M, Shigematsu Y, Kodama K, Hara Y, Kuwahara T, Hashida H, Ikeda S, Ohtsuka T, Sasaki O, Hiwada K. Systolic time intervals can detect patients with angina pectoris at high risk. Jpn J Appl Physiol. 1997;27:51–60.

5. Kodama K, Hamada M, Hiwada K. Transient leftward QRS axis shift during treadmill exercise testing or percutaneous transluminal coronary angioplasty is a highly specific marker of proximal left anterior descending coronary artery disease. Am J Cardiol. 1997;79:1530–1534.[Medline] [Order article via Infotrieve]

6. Knight C, Kurbaan AS, Seggewiss H, Henein M, Gunning M, Harrington D, Fassbender D, Gleichmann U, Sigwart U. Nonsurgical septal reduction for hypertrophic obstructive cardiomyopathy: outcome in the first series of patients. Circulation. 1997;95:2075–2081.[Abstract/Free Full Text]

Response

Ulrich Sigwart, MD, FRCP, FESC; Derek Gibson, MD, FRCP, FESC; Michael Henein, MD; ; Robert Anderson, MD, FRCP, FESC

Royal Brompton Hospital, Department of Invasive Cardiology, London, England

We thank Dr Hamada and his colleagues for their interest in our article on nonsurgical septal reduction in patients with hypertrophic obstructive cardiomyopathy¹ and entirely agree with them that the procedure provides a unique opportunity to observe the electrophysiological consequences of occlusion of the first septal branch of the left anterior descending coronary artery.¹

In answer to their questions, we noted that an axis shift to the left of -30° occurred in 3 of our patients and that this was still present 6 months after the procedure. The most common ECG consequence of occlusion of the first septal branch was the development of complete right bundle-branch block, which immediately appeared in 11 patients and persisted at 6 months. The anatomic basis for this is demonstrated in the dissection of 2 normal hearts (Figure ). These are orientated to match the bodily coordinates and show the relationship between the first septal perforating artery (arrow in a, double dotted lines in b) relative to the septal structures. In both hearts, the freestanding pulmonary infundibulum has been removed, and further dissection has revealed the site of the membranous septum in b. The single dotted line shows the course of the right bundle-branch block, with the crosshatches showing the branching component of the ventricular conduction axis.

The variations of blood supply through septal perforators to the conduction system are the basis for the occurrence of conduction disorders. Alcohol injection into the first septal perforator seems to affect the right bundle most frequently.

References

1. Knight C, Kurbaan AS, Seggewiss H, Henein M, Gunning M, Harrington D, Fassbender D, Gleichmann U, Sigwart U. Nonsurgical septal reduction for hypertrophic obstructive cardiomyopathy: outcome in the first series of patients. Circulation. 1997;95:2075–2081.

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