Left Ventricular Fibromuscular Band Is Not a Specific Substrate for Idiopathic Left Ventricular Tachycardia
Background A fibromuscular band has been detected in patients with idiopathic left ventricular tachycardia, and this band has been suggested to be the anatomic substrate for the arrhythmia. Whether the fibromuscular band is a specific substrate for the tachycardia was systematically evaluated in a large group of consecutive patients with and without idiopathic left ventricular tachycardia.
Methods and Results Conventional transthoracic two-dimensional echocardiography and multiplane transesophageal echocardiography were performed in 18 patients with idiopathic left ventricular tachycardia that was responsive to calcium blockers (group 1, tachycardia patients) and 40 patients with paroxysmal supraventricular tachycardia (group 2, control patients). There were 17 men and 1 woman, with a mean age of 29±11 years, in group 1 patients, and 21 men and 19 women, with a mean age of 42±12 years, in group 2 patients. The QRS morphology during tachycardia in group 1 patients displayed a pattern of right bundle-branch block with superior axis in 15 patients, indeterminate axis in 2 patients, and inferior axis in 1 patient. Radiofrequency ablation successfully eliminated the tachycardia in all 18 patients; the successful ablation site was located at the inferior apical septum in 11 patients, at the midseptum in 6 patients, and at the anterior lateral wall in 1 patient. Transthoracic echocardiography detected the fibromuscular band in 11 of the 18 patients, whereas multiplane transesophageal echocardiography detected the band in 17 of 18 patients. The fibromuscular band extended from the interventricular septum to the apex of the left ventricle. In group 2 patients, transthoracic echocardiography detected the fibromuscular band in 22 and multiplane transesophageal echocardiography detected the band in 35 of the 40 patients. The presence of a fibromuscular band in these two groups of patients was not statistically different.
Conclusions The presence of a left ventricular fibromuscular band is not a specific anatomic substrate for idiopathic left ventricular tachycardia.
Idiopathic left ventricular tachycardia is a unique entity characterized by a QRS morphology of right bundle-branch block with superior axis and responsiveness to calcium blockers.1 2 Reentry appears to be the physiological substrate for this arrhythmia. However, the anatomic substrate is less clear. It has been shown that a fibromuscular band is frequently found in patients with idiopathic left ventricular tachycardia and that this fibromuscular band could be the anatomic substrate for this arrhythmia.3 4 In the present study, we used multiplane transesophageal echocardiography to prospectively examine a large group of patients with and without idiopathic left ventricular tachycardia to evaluate whether the left ventricular fibromuscular band is a specific substrate for idiopathic left ventricular tachycardia.
The study population consisted of 58 consecutive patients: 18 with (group 1) and 40 without (group 2) idiopathic left ventricular tachycardia. None of the 58 patients had evidence of structural heart disease as determined by cardiac examination, chest radiograph, resting ECG, and echocardiogram. The study protocol was reviewed and approved by the institutional review board and was in accordance with local ethical standards. Of the 18 patients with idiopathic left ventricular tachycardia, there were 17 men and 1 woman, with a mean age of 29±11 years. All 17 patients had clinical documentation of wide QRS tachycardia with a QRS morphology of right bundle-branch block that was responsive to verapamil; 15 displayed a superior axis, 2 an indeterminate axis, and 1 an inferior axis. All 18 patients underwent electrophysiological study that was followed by radiofrequency ablation therapy. Of the 40 patients without idiopathic left ventricular tachycardia, there were 21 men and 19 women, with a mean age of 42±12 years. All 40 patients had clinical documentation of paroxysmal supraventricular tachycardia, 23 with atrioventricular node reentry tachycardia and 17 with atrioventricular reentrant tachycardia incorporating an accessory pathway (left in 11 and right in 6), and all underwent radiofrequency ablation therapy because of troublesome tachycardias. Patients with idiopathic left ventricular tachycardia were significantly younger than the control patients, and there was a male dominance in patients with idiopathic left ventricular tachycardia.
All 56 patients received conventional transthoracic echocardiographic and multiplane transesophageal echocardiographic examinations in the left lateral decubitus position 2 to 3 days after radiofrequency ablation before discharge. The 18 patients with idiopathic left ventricular tachycardia also received two-dimensional transthoracic echocardiographic examinations immediately after radiographic recordings of the successful ablation site during the ablation session. The Hewlett-Packard Multiplane Sonos-1500 system (Hewlett Packard Co, Medical Products Group) was used in all patients. The insertion and operation of the transducer, the examination technique, and the imaging techniques are similar to those of conventional transesophageal echocardiography.5 6 7 The imaging notation and orientation were performed with the sector apex kept at the top of the monitor throughout the examination. The cardiac structure closer to the transducer was displayed at the top of the monitor, and the anatomic left-sided structure was displayed on the left side of the monitor.
The diagnosis of left ventricular fibromuscular bands was made when a stringlike linear structure with a free cavity course was observed.8 9 10 11 12 These bands are not related to the mitral valve and connect to the interventricular septum, the left ventricular apex, or the left ventricular free walls. In each patient, the length and the width of the fibromuscular band were measured carefully.
In all 18 group 1 patients with idiopathic left ventricular tachycardia, the tachycardia was successfully eliminated by radiofrequency ablation. The successful ablation site was located at the inferior apical septum in 11 patients, at the midseptum in 6 patients, and at the anterior lateral wall in 1 patient. In all 18 patients, the successful ablation site was documented by radiographic recordings as well as by conventional two-dimensional echocardiographic recordings during ablation. The predischarge conventional two-dimensional transthoracic echocardiographic examination detected the presence of a fibromuscular band in 11 of the 18 patients, whereas the multiplane transesophageal echocardiographic examination detected the fibromuscular band in 17 of the 18 patients (Fig 1⇓). Fifteen patients had a single band and two had two bands; thus, a total of 19 fibromuscular bands were noted. The fibromuscular band extended from the upper interventricular septum to the apex of the left ventricle in 11, from the upper septum to the lateral apical area of the left ventricle in 3, from the midseptum to the apex of the left ventricle in 3, from the midseptum to the lateral apical area of the left ventricle in 1, and from the low septum to the apex of the left ventricle in 1. The length of the fibromuscular band was 39.6±11.3 mm, and the width was 3.8±0.96 mm. In none of the patients was the successful ablation site located at the site of septal or apical insertion of the band. In the 40 control patients without idiopathic left ventricular tachycardia, conventional two-dimensional echocardiography detected the presence of the fibromuscular band similar to that seen in group 1 tachycardia patients in 22 of the 40 patients, whereas the multiplane transesophageal echocardiography detected the fibromuscular band in 35 of the 40 patients (Fig 2⇓). Patients without the fibromuscular band tended to be older than those with the band (48±6 versus 42±13 years, P=.09 by Mann-Whitney test); however, there was no sex difference between patients with or without the presence of the fibromuscular band (P=.45 by Fisher’s exact test). When patients with a right-sided accessory pathway or atrioventricular node reentry tachycardia, in whom electrode catheters were not inserted into the left ventricle, were compared with those with a left-sided accessory pathway, the presence of a fibromuscular band was not different in these patients (P=.22 by Fisher’s exact test). Thirty-three patients had a single band and two had two bands; thus, a total of 37 fibromuscular bands were noted. The fibromuscular band extended from the upper interventricular septum to the apex of the left ventricle in 17, from the upper septum to the lateral apical area of the left ventricle in 4, from the midseptum to the apex of the left ventricle in 11, from the midseptum to the lateral apical area of the left ventricle in 1, from the low septum to the apex of the left ventricle in 3, and from the low septum to the lateral apical area of the left ventricle in 1. The length of the fibromuscular band was 33.9±8.3 mm, and the width was 3.0±0.8 mm. The length of the fibromuscular band was longer in men (37.5±7.8 versus 30.1±7.2 mm, P=.006), but the width of the band was similar in male and female control patients (3.0±0.8 versus 3.0±0.8 mm, P=.63 by Mann-Whitney test). The presence of a fibromuscular band in group 1 and group 2 patients was not statistically different (P=.39 by Fisher’s exact test). However, the length of the band tended to be longer (P=.06) and the width of the band was wider (P=.002) in group 1 patients (Mann-Whitney test).
Idiopathic Left Ventricular Tachycardia
A unique type of left ventricular tachycardia displaying a QRS morphology of right bundle-branch block with superior axis and occurring in patients without obvious structural heart disease was designated as a specific entity by Lin et al in 1983.1 This tachycardia is inducible and terminable with programmed stimulation and can be entrained by overdrive pacing from the right ventricular outflow tract.1 2 12 It is responsive to calcium blockers but not to adenosine.13 Reentry involving slow-response tissue is likely to be the underlying operative mechanism. The exit site appears to be located at the inferoapical region of the left interventricular septum. Mapping at the exit site or near the exit site almost always reveals a sharp spike that precedes the ventricular electrogram.14 15 16 Radiofrequency ablation with application of currents to the exit site, where the spike is the earliest, occurring ≥30 milliseconds before the ventricular electrogram, and where the pace-map 12-lead ECG displays a QRS morphology resembling that during tachycardia, is very effective in eradicating the tachycardia.15 16 However, successful ablation has also been achieved with application of currents to sites where the pace-map 12-lead ECG shows a QRS morphology that is not identical to that during tachycardia.15 17 These observations suggest that the reentry circuit may be of considerable size and that the His-Purkinje system may be a part of the circuit (at least the exit site).
The etiology of this arrhythmia is unclear. Familial cluster of this arrhythmia has not been noted, and genetic transmission of this disease is unlikely. Cardiac examination, resting ECG, chest radiograph, and cardiac catheterization unanimously show no apparent abnormality in these patients. However, Nagao et al18 conducted endomyocardial biopsies in two patients with idiopathic left ventricular tachycardia and demonstrated nonspecific myocardial degeneration in both right and left ventricles. The significance of these findings is unclear. The male predominance and the younger age of the patients with idiopathic left ventricular tachycardia have not been discussed previously. However, in a total of 57 patients discussed previously in several reports,1 2 12 14 15 16 40 were men and 17 were women. The mean age of the patients in these reported series ranged from 26±10 to 31±14 years, and none were older than 50 years. This latter finding suggests that idiopathic left ventricular tachycardia may subside spontaneously with aging.
Fibromuscular bands have been observed in normal and abnormal hearts. Of patients undergoing echocardiographic examinations, Nishimura et al8 reported an incidence of 0.5% in 1000 patients; Perry et al9 reported an incidence of 0.8% in 3847 patients; Vered et al10 reported an incidence of 2% in 2079 patients; and Suwa et al11 reported an incidence of 2% in 1117 patients. In contrast, Okumura et al12 reported an incidence of 61% in 100 consecutive infants and children. The low incidence of left ventricular fibromuscular bands as defined by echocardiography in the series of Nishimura et al,8 Perry et al,9 Vered et al,10 and Suwa et al11 may be, in part, related to the retrospective nature of the study. In a subsequent prospective study by Suwa et al,19 the incidence was 71% in 187 healthy adults. However, there was only one retrospective study in which the accuracy of echocardiography in the diagnosis of left ventricular fibromuscular bands was assessed. Keren et al20 evaluated the reliability of two-dimensional echocardiography in 35 patients who underwent cardiac transplantation and pathological examination and showed an incidence of 37% with a sensitivity of 85%, a specificity of 82%, a positive predictive value of 73%, and a negative predictive value of 90%.
The presence of left ventricular fibromuscular bands is usually considered to be of no clinical significance. However, Suwa et al3 described a patient with idiopathic left ventricular tachycardia in whom a fibromuscular band was noted extending from the basal interventricular septum to the inferior endocardium near the apex. The earliest ventricular activation during ventricular tachycardia in this patient appeared to correspond to the apical insertion of the fibromuscular band. Surgical removal of this band along with the application of cryocoagulation around the apical insertion site of the band cured the tachycardia. Histopathological examination of this band revealed numerous Purkinje fibers and a few monocytes possibly related to degeneration. They suggested that this fibromuscular band was related to the genesis of ventricular tachycardia. Thakur et al4 prospectively performed transthoracic and transesophageal echocardiographic examinations in 8 patients undergoing radiofrequency ablation for idiopathic left ventricular tachycardia. A fibromuscular band extending from the posteroinferior apical region to the interventricular septum was observed in all 8 patients. They suggested that this fibromuscular band is the anatomic substrate for idiopathic left ventricular tachycardia. Similar to the study of Thakur et al,4 this study found that 17 of the 18 patients with idiopathic left ventricular tachycardia demonstrated left ventricular fibromuscular bands; however, the band was also observed in 35 of the 40 patients without idiopathic left ventricular tachycardia. Thus, the fibromuscular band is not a specific substrate for idiopathic left ventricular tachycardia. Nevertheless, the present study does not exclude the possibility that the fibromuscular band may be involved as a part of the circuit in the genesis of ventricular tachycardia. The finding of the fibromuscular band being longer and wider in patients with idiopathic left ventricular tachycardia may be, in part, explained on the basis of male dominance in these patients because the band was longer in the male control patients.
The present study has some limitations. Although the successful ablation sites were located away from the sites of septal or apical insertion of the fibromuscular band, the bands could have discrete connections with the septum that were not visualized by the echocardiographic techniques. Thus, it is possible that ablation at discrete points on the septum along the band would result in successful ablation. Also, the radiofrequency energy was not delivered to the site of insertion, and, therefore, the possibility that the band was a part of the circuit could not be excluded. Last, multiplane transesophageal echocardiography was not done at the time of radiofrequency ablation, and, thus, the distance between the successful ablation site and the insertion site of the band could not be accurately measured, although it was at least 1 cm as determined with both angiography and transthoracic echocardiography, which were performed at the time of ablation.
The left ventricular fibromuscular band as recognized with the use of multiplane transesophageal echocardiography is a common finding in the general population and probably has no special clinical significance. It is not a specific anatomic substrate for idiopathic left ventricular tachycardia, although it could be a potential substrate.
This work was supported in part by grants from the National Health Institutes (DOH 84-HR-205) and the National Science Council (NSC 84-2331-B-182-009 and NSC 84-2331-B-182-003) of the Republic of China, Taipei.
Reprint requests to Delon Wu, MD, Chang Gung Memorial Hospital, 199 Tung Hwa North Rd, Taipei, Taiwan.
- Received July 10, 1995.
- Revision received September 18, 1995.
- Accepted September 24, 1995.
- Copyright © 1996 by American Heart Association
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