Novel Coronary Artery Anomaly in an English Bulldog with Pulmonic Stenosis

Abstract

A 5-month-old female intact English Bulldog was referred for evaluation and management of congenital cardiac disease. On physical examination, body weight was 12.3 kg, body temperature was 101.8°F, and arterial pulse was 120 bpm. A 4/6 systolic ejection murmur was heard best over the left heart base, but radiated toward the sternum and also could be heard over the right hemi-thorax. An umbilical hernia was present, but the remainder of the physical examination was unremarkable. Thoracic radiographs were obtained. Based on subjective evaluation, the cardiac silhouette was enlarged. Breed-associated developmental abnormalities of the vertebrae were identified and therefore the size of the cardiac silhouette was not evaluated by calculation of a vertebral heart score. In the context of the phase of respiration during which the exposure was made, the pulmonary vessels and parenchyma were considered normal. Transthoracic echocardiography was performed. There was marked, diffuse right ventricular hypertrophy and, as a result, the infundibulum was narrow. Subjective evaluation disclosed moderate right atrial enlargement. Poststenotic dilatation of the main pulmonary artery was present. The distance between the hinge points of the pulmonary valve leaflets visible in a right parasternal short-axis image was 9 mm whereas the diameter of the aortic root in the same image plane was 17 mm. Thus, the diameter of the pulmonary valve annulus was small relative to that of the aorta (Ao : PA >1.2). The pulmonary valve leaflets were thick yet mobile. Pulsed wave Doppler interrogation of right ventricular outflow guided by a right parasternal short-axis image disclosed a discrete velocity step-up at the pulmonic valve. Examination by continuous wave Doppler provided a peak right ventricular outflow tract (RVOT) velocity of 5.5 m/s, a finding that corresponds to a pressure gradient of 120 mmHg across the RVOT. Mild tricuspid valve regurgitation was identified, but it was not possible to determine the peak velocity of this jet. Small end-diastolic and end-systolic left ventricular dimensions (19.2 and 10 mm, respectively) were attributed to decreased pulmonary venous return. The coronary sinus was dilated. Agitated saline was injected into the left cephalic vein during echocardiography and the resultant contrast echocardiogram provided evidence of a right-to-left interatrial shunt. The coronary sinus was opacified suggesting persistence of the left cranial vena cava. The diagnosis was severe pulmonic stenosis associated with patent foramen ovale and persistent left cranial vena cava. Echocardiographic correlates of a single coronary artery ostium were not identified.1 However, aortography was planned for the next day based on the reported association between pulmonic stenosis and the presence of a single coronary ostium in brachycephalic dogs.1, 2 Balloon dilatation of the RVOT was to be considered depending on the angiographically defined coronary configuration. After induction of general anesthesia, the left femoral artery was isolated and then exteriorized through a small inguinal incision. A short, 5 French (F) sheath-introducer system was placed through an arteriotomy and a 5 F pigtail angiographic catheter was advanced over a 0.035 in wire guide to the ascending aorta. A lateral, proximal aortogram was recorded after injection of 12 mL iodinated contrast medium. A coronary artery anomaly (CAA) was present (Fig 1). Specifically, all coronary arteries arose from a single cranial ostium. The vessel that followed the typical course of the left circumflex artery crossed the aortic sinus, but circumpulmonary coronary branches were not apparent. From the putative left cirumflex artery arose a caudal vessel that coursed caudoventrally in the region of the subsinuosal interventricular sulcus. A 6 F sheath-introducer system then was percutaneously placed in the right external jugular vein. A right ventriculogram was recorded after the tip of a 5 F flow-directed angiographic catheter was advanced to the body of the right ventricle. The noninvasive diagnosis of valvular pulmonic stenosis was confirmed; the systolic angiographic diameter of the annulus was approximately 9.8 mm (Fig 2). Contrast delineation of the RVOT and pulmonary artery provided confirmation that the coronary arteries did not encircle the infundibulum (Fig 3). Balloon dilatation of the PS then was performed. Briefly, the stenosis was crossed with a 6 F flow-directed end-hole catheter. This catheter ultimately was exchanged over a 260 cm (0.035 inch) wire guide for 3 different catheters that carried 10 mm × 3 cm, 12 mm × 2 cm, or 15 mm × 3 cm valvuloplasty balloons. Although the choice of balloon initially was conservative, balloons that had diameters that exceeded the diameter of the pulmonary artery ultimately were used. Each balloon was positioned across the stenosis using fluoroscopic guidance and multiple inflations were performed. Right ventricular pressures were evaluated after use of each balloon catheter but little change was evident. During the final inflation of the 15 mm × 3 cm balloon, a distinct “waist” developed, but the balloon ruptured immediately afterward. Complications were not seen. The obstructive gradient during an echocardiogram the day after the procedure was similar (136 mmHg) to that recorded the day before. Presumably, the change in gradient reflected measurement variability and not worsening of the stenosis. The fact that an “oversized balloon” (at least 150% of the pulmonary annulus) was inflated to burst pressure, but failed to dilate the stenosis, suggested that the lesion may not have been amenable to the procedure. It is possible, however, that a high-pressure balloon or a balloon of a different size might have been more effective. The dog has not been seen at our hospital since January 2011, but was reportedly alive as of May 2013 and had undergone ovariohysterectomy and umbilical hernia repair without complications. We identified a previously unreported canine CAA consisting of a single right ostium that gave rise to arteries that lacked circumpulmonary branches. The coronary circulation was right dominant. Benign variations of coronary anatomy in dogs and humans make the distinction between normal variants and anomalies difficult.3 For example, the presence of 2 coronary ostia within the left aortic sinus that give rise to the left paraconal and left circumflex arteries is identified in approximately 8% of dogs.4 This variation is considered to be benign as is the analogous coronary configuration in humans.3, 4 The normal coronary configuration, however, consists of 2 main coronary arteries that arise from the right and left aortic sinuses.4 Typically, the circumflex and paraconal interventricular arteries are branches of the left common coronary artery. The subsinuosal interventricular or caudal descending artery follows the subsinuosal interventricular sulcus. This artery is analogous to the caudal descending artery of humans and, in anatomically normal dogs, arises from the left circumflex artery.4 In humans, the origin of the caudal descending artery determines the “dominance” of the coronary circulation. In approximately 80% of humans the caudal descending artery arises from the right circumflex artery, and this configuration is said to be “right dominant”.5 Anatomically normal dogs have a left dominant coronary circulation.4 In humans, coronary artery anomalies have been categorized as follows: (1) anomalies of origination or course; (2) intrinsic abnormalities of coronary anatomy that include aneurysms and stenosis; (3) anomalies of coronary termination including fistulae; and (4) anomalous anastomotic vessels.3 A number of subtly different schemata have been proposed to categorize anomalies of origination or arterial course. The presence of a single right coronary ostium that gives rise to a circumpulmonary left coronary artery has been described as type IIB1, type R4A and, by Lipton, as an R2A anomaly.6-8 A modification of Lipton's scheme was used by Buchanan to describe this coronary anomaly identified in association with pulmonic stenosis in brachycephalic dogs and the use of the R2A descriptor is widespread in the veterinary literature.1 Canine CAAs have been described infrequently. The first appearance of CAA in the literature was in 1959; a single right coronary ostium associated with right dominant coronary circulation was detected incidentally during postmortem examination of a mongrel dog that reportedly had been in good health.9 A CAA consisting of a single right coronary ostium also was identified during an embryologic investigation of the pathogenesis of truncus arteriosus in a keeshond.10 In a recent retrospective study of congenital canine heart disease, an anomalous right coronary artery was present alone or in combination with other congenital defects in 9 of 1,132 (0.08%) dogs, and all that could be characterized were described as R2A. Two of 9 of these anomalies were isolated findings, and 7/9 were identified in conjunction with pulmonic stenosis, but the circumstances that led to the identification of the isolated coronary anomalies were not described.11 A CAA in a dog with PS was reported in 1965, but the clinical implications of the association between the R2A anomaly and canine pulmonic stenosis were first described in 1989.2, 12 In the latter case, as in 2 others reported in 1990, the anomaly was identified when a surgical patch graft procedure intended to palliate severe pulmonic stenosis resulted in intraoperative death because of transection of the circumpulmonary artery.1 The R2A anomaly also may pose a contraindication to balloon dilatation of associated pulmonic stenosis because coronary artery avulsion after transcatheter intervention has been reported.13 However, this complication did not occur in 4 English Bulldogs with PS and a single right coronary ostium that were subjected to valvuloplasty using balloons the diameter of which approximated that of the pulmonary valve.14 The R2A anomaly may have etiologic relevance because it has been hypothesized that the circumpulmonary branch compresses the conus arteriosus in utero resulting in a hypoplastic pulmonary annulus and valvular pulmonic stenosis.15 Associated echocardiographically evident abnormalities can include a hypoplastic right pulmonary leaflet, small left aortic sinus with small associated aortic leaflet, a disproportionately large right aortic leaflet, and a subvalvular linear structure that represents the circumpulmonary branch.1 All documented cases of the R2A anomaly identified in association with pulmonic stenosis have been in brachycephalic dogs, specifically English Bulldogs and Boxer dogs, a finding that suggests a genetic basis for the association.1, 2 For purposes of comparison to the anomaly described herein, examples of the R2A anomaly and of normal coronary artery configuration are angiographically shown (Fig 4 and 5). In humans, origination of the left main coronary artery from the right aortic sinus has clinical relevance particularly when the course of the left circumflex artery is between the aorta and right ventricular outflow tract because this arrangement is associated with a risk of sudden death and myocardial ischemia.16 Of the single right coronary ostium variants that have been described in people, it is not clear which was observed in our patient. Using the classification scheme that has been published in the veterinary literature, the anomaly was apparently an R2B or R2C. In the former, the left main coronary artery follows a course between the aorta and pulmonary artery and, in the latter, the left main coronary artery is to the right and caudal to the aorta. Oblique angiograms might have more precisely defined the anomaly but were not recorded. Perhaps more extensive imaging studies would have provided clarity. In general, ventrodorsal projections of aortiograms rarely provide diagnostically useful descriptions of canine coronary anatomy.17 It would have been interesting to evaluate the patient by cardiac magnetic resonance imaging, but this modality was not available to us. To our knowledge, this is the first description of a CAA other than R2A in a dog with pulmonic stenosis. Although there was a single right ostium, the coronary branches were not circumpulmonary. The diversity of anomalous coronary configurations that occur in association with canine PS apparently is greater than currently recognized, and this finding might have therapeutic implications. Conflict of Interest: Authors disclose no conflict of interest.