Pulmonary artery banding in a cat with a perimembranous ventricular septal defect and left-sided congestive heart failure

Brandy N. Cichocki Department of Veterinary Clinical Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078.

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Danielle R. Dugat Department of Veterinary Clinical Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078.

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Ryan D. Baumwart Department of Veterinary Clinical Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078.

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Abstract

CASE DESCRIPTION A 6-month-old sexually intact male domestic shorthair cat was referred for evaluation of a heart murmur and ventricular septal defect (VSD).

CLINICAL FINDINGS Physical examination revealed a grade 5/6 right apical systolic heart murmur. Findings on thoracic radiography were consistent with moderate right and left ventricular enlargement, left atrial enlargement, and enlargement of the pulmonary arteries and veins; an interstitial pulmonary pattern was also evident. Echocardiography revealed a perimembranous VSD with left-to-right shunting combined with trace mitral valve regurgitation. The cat later developed a dry cough, the intensity of the heart murmur increased to grade 6/6, and signs of left-sided congestive heart failure developed.

TREATMENT AND OUTCOME Medical treatment included enalapril maleate and furosemide. When the cat's condition worsened despite medical treatment, palliative pulmonary artery banding was performed. During surgery, blood pressure in the pulmonary artery was measured with a pulmonary artery catheter, and pulmonary artery banding was successfully achieved with a polytetrafluoroethylene band and hemoclips. The pulmonary-to-systemic blood flow ratio was reduced from 3 to 1.5, and signs of congestive heart failure resolved within 2 weeks after surgery.

CLINICAL RELEVANCE Findings suggested that cats with a VSD and pulmonary-to-systemic flow ratio > 3 or with congestive heart failure attributable to a VSD could be considered candidates for palliative pulmonary artery banding to alleviate clinical signs. However, further investigation into long-term prognosis with objective outcome measurements and with multiple cases is needed. (J Am Vet Med Assoc 2019;254:723–727)

Abstract

CASE DESCRIPTION A 6-month-old sexually intact male domestic shorthair cat was referred for evaluation of a heart murmur and ventricular septal defect (VSD).

CLINICAL FINDINGS Physical examination revealed a grade 5/6 right apical systolic heart murmur. Findings on thoracic radiography were consistent with moderate right and left ventricular enlargement, left atrial enlargement, and enlargement of the pulmonary arteries and veins; an interstitial pulmonary pattern was also evident. Echocardiography revealed a perimembranous VSD with left-to-right shunting combined with trace mitral valve regurgitation. The cat later developed a dry cough, the intensity of the heart murmur increased to grade 6/6, and signs of left-sided congestive heart failure developed.

TREATMENT AND OUTCOME Medical treatment included enalapril maleate and furosemide. When the cat's condition worsened despite medical treatment, palliative pulmonary artery banding was performed. During surgery, blood pressure in the pulmonary artery was measured with a pulmonary artery catheter, and pulmonary artery banding was successfully achieved with a polytetrafluoroethylene band and hemoclips. The pulmonary-to-systemic blood flow ratio was reduced from 3 to 1.5, and signs of congestive heart failure resolved within 2 weeks after surgery.

CLINICAL RELEVANCE Findings suggested that cats with a VSD and pulmonary-to-systemic flow ratio > 3 or with congestive heart failure attributable to a VSD could be considered candidates for palliative pulmonary artery banding to alleviate clinical signs. However, further investigation into long-term prognosis with objective outcome measurements and with multiple cases is needed. (J Am Vet Med Assoc 2019;254:723–727)

A 6-month-old 2.92-kg (6.42-lb) sexually intact male domestic shorthair cat was referred to the Boren Veterinary Medical Teaching Hospital of the Oklahoma State University for evaluation of a grade 5 (on a scale of 1 to 6) right apical systolic heart murmur. In the 2 weeks prior to this initial evaluation, the cat's heart murmur had been detected by the referring veterinarian during a routine wellness examination for vaccination; however, no abnormal clinical signs had been reported by the owner. Because of the heart murmur, the referring veterinarian performed thoracic radiography, which revealed mild left-sided heart enlargement and a diffuse interstitial lung pattern. Echocardiography was also performed by the referring veterinarian and revealed a defect in the ventricular septum. At that point, treatment with enalapril maleate (0.85 mg/kg [0.39 mg/lb], PO, q 24 h) and amlodipine besylate (0.85 mg/kg, PO, q 24 h) was initiated even though no hypertension was found, and the cat was referred for further evaluation.

On initial examination by a cardiologist at the veterinary teaching hospital, the cat had a body condition score of 3 (on a scale of 1 to 5), a heart rate of 150 beats/min (reference range, 140 to 220 beats/min), mild tachypnea (45 breaths/min; reference range, 20 to 30 breaths/min), a grade 5/6 right apical systolic heart murmur, and good, synchronous femoral pulses. Thoracic radiography was performed, and findings were consistent with moderate right and left ventricular enlargement, moderate left atrial enlargement, and enlargement of the pulmonary vasculature. In addition, an improved interstitial lung pattern was identified, compared with the pattern identified on radiographs obtained by the referring veterinarian. Echocardiography performed by the cardiologist revealed a perimembranous VSD (Figure 1) with a maximum shunt velocity of 5.31 m/s as well as trace mitral valve regurgitation. Left ventricular systolic function, as estimated by the percentage of fractional shortening (39%; reference range, 25% to 40%1), was normal; however, the cat did have mild to moderate left atrial dilation (diameter, 1.79 cm; reference range, 1.09 to 1.37 cm) and left ventricular dilation (left ventricular internal dimension at diastole, 1.9 cm [reference range, 1.40 to 1.78 cm]; left ventricular internal dimension at systole, 1.2 cm [reference range, 0.64 to 0.96 cm]).2 The Qp:Qs, calculated from the aortic and pulmonic 2-D and spectral Doppler ultrasonic mode tracings, was 3, indicating a large left-to-right shunt.3 In addition, given the radiographic findings, left-sided congestive heart failure was suspected; however, pneumonia had not yet been ruled out. Amoxicillin–clavulanate potassium (15 mg/kg [6.8 mg/lb], PO, q 12 h for 2 weeks) was prescribed, amlodipine was discontinued because no systemic hypertension was noted, and the enalapril dosage was reduced (0.43 mg/kg [0.20 mg/lb], PO, q 24 h).

Figure 1—
Figure 1—

Long-axis 2-D (A) and color-flow Doppler mode (B) echocardiographic images obtained from the right parasternal transducer location in a 2.92-kg (6.42-lb) sexually intact male domestic shorthair cat with a grade 5/6 right apical systolic heart murmur and a perimembranous VSD (arrow) through which blood shunted from the left ventricle to the right ventricle. LV = Left ventricle. RV = Right ventricle.

Citation: Journal of the American Veterinary Medical Association 254, 6; 10.2460/javma.254.6.723

Six weeks later, a recheck examination was performed by the cardiologist. Since the last appointment, the cat had developed a dry cough with episodes that occurred > 2 times/wk. However, no signs of exercise intolerance were reported by the owner, and the cat's body weight had increased to 4.16 kg (9.15 lb). The cat's heart rate was 180 beats/min, but the cat was tachypneic (80 breaths/min). Thoracic auscultation also revealed an unchanged grade 5/6 right apical systolic heart murmur. Given the cat's change in respiratory rate combined with its previous medical history, left-sided congestive heart failure was suspected. Diagnostic imaging was not performed at this visit so as to not stress the cat; however, furosemide (1.2 mg/kg [0.55 mg/lb], PO, q 12 h for 3 days, then q 24 h) was initiated.

A week later (7 weeks after initial evaluation), the cat was returned for thoracic radiography and serum biochemical analyses. Medical treatment at the time included the previously prescribed once-daily enalapril and furosemide. On examination, the cat's respiratory rate was improved (52 breaths/min), compared with that of the previous visit, and the cat's heart rate was 160 beats/min. Thoracic auscultation revealed a change in the intensity of the right apical systolic heart murmur from grade 5/6 noted previously to grade 6/6. Femoral pulses were fair and synchronous. Thoracic radiography revealed left atrial enlargement, moderate right ventricular enlargement, mild to moderate enlargement of the pulmonary vasculature, a mild interstitial pattern in the cranial lung lobes, and a bronchointerstitial lung pattern in the perihilar region and caudodorsal lung fields. Results of the serum biochemical analyses were within reference limits. Consultation with the surgery department for pulmonary artery banding was recommended.

The next week (8 weeks after the initial cardiac consultation), the cat was evaluated by the surgical team. Results of the physical examination, including thoracic auscultation, were unchanged from the previous week. Thoracic radiography was repeated and revealed resolution of the mild pulmonary vascular distention and improvement of the bronchointerstitial pattern at the perihilar region but continued left atrial enlargement and moderate right ventricular enlargement. Surgical treatment with pulmonary artery banding as a palliative procedure to reduce the recurrence of clinical signs related to left-sided congestive heart failure was discussed and scheduled for a month later.

Twelve weeks after the initial cardiac consultation, the cat was admitted for surgical treatment. Results of the physical examination the day before surgery indicated no change to the intensity of the cat's heart murmur or femoral pulses. On the day of surgery, the cat was premedicated with tiletaminezolazepam (2.0 mg/kg [0.91 mg/lb], IM) and hydromorphone (0.05 mg/kg [0.023 mg/lb], IM), and anesthesia was induced with alfaxalone (2.0 mg/kg, IM). Endotracheal intubation was performed, and a surgical plane of anesthesia was maintained with isoflurane in oxygen delivered through the endotracheal tube combined with a constant rate infusion of fentanyl citrate (1.5 μg/kg/h [0.68 μg/lb/h]), midazolam (1.0 mg/kg/h [0.45 mg/lb/h]), and ketamine (0.05 mg/kg/h). Intravenous isotonic crystalloid fluidsa were provided at a rate of 3.0 to 5.0 mL/kg/h (1.36 to 2.27 mL/lb/h). Heart rate, continuous direct arterial blood pressure, ventilation, pulse oximetry, and end-tidal CO2 were monitored. Cefazolin sodium (22.0 mg/kg [10 mg/lb], IV, q 90 min) was administered perioperatively, with the first dose being administered just after anesthetic induction.

Briefly, a left fifth intercostal thoracotomy was performed to assess the main pulmonary artery. The pericardium was opened ventral to the phrenic nerve, which was retracted dorsally. A right-angle forceps was used to bluntly dissect the main pulmonary artery from the aorta cranially. Once the surrounding adventitia was completely dissected, a right-angle forceps was used to pass a 2- to 3-mm-wide × 0.5-mm-thick × 90-mm-long band of expanded PTFEb medial to the pulmonary artery, approximately 0.5 cm dorsal to the pulmonic valve. Just distal to that, 5-0 polydioxanone on a tapered needle was used to place a mattress suture incorporating PTFE felt pledgetsc on the main pulmonary artery. Once the pledgets were in place, a 25-gauge IV catheter with a stylet was placed through the center of the mattress suture and into the main pulmonary artery. The stylet was removed, and the catheter was connected to an anesthetic machine capable of directly measuring blood pressure.d The initial blood pressure in the pulmonary artery was 30 mm Hg (reference range, 12 to 17 mm Hg4). Next, the diameter of the pulmonary artery was slowly reduced by tightening the expanded PTFE band, while simultaneously monitoring the pressure in the pulmonary artery. The pulmonary artery diameter was reduced by 15% to 20% with no change in pressure detected. Intraoperative transcardiac echocardiography was then performed to evaluate the shunt velocity and provide a better indicator of optimal artery diameter reduction. The PTFE band was initially secured with a hemostatic clip and was tightened further by securing each new clip in an alternating pattern, where each new clip (total of 4) was placed on alternating sides of the PTFE to ultimately achieve a 40% reduction in diameter of the main pulmonary artery. As a result, the shunt velocity decreased from 5.31 to 3.23 m/s. The catheter was removed from the pulmonary artery while the horizontal mattress suture at the catheter site was tightened. The thoracic wall was closed, and before the cat was recovered from anesthesia, residual free air in the thoracic cavity was removed by thoracocentesis with a 19-gauge butterfly catheter attached to a 3-way stopcock that was connected to a 35-mL syringe.

Total surgery time was 129 minutes. No intraoperative complications related to placement of the pulmonary artery band occurred, and hypotension was the only anesthetic complication encountered. The mean arterial pressure at its lowest point was 55 mm Hg, and dobutamine (2.0 to 4.0 μg/kg/h [0.91 to 1.82 μg/lb/h]) was administered to correct the hypotension.

Postoperative care consisted of placement of the cat in an oxygen cage set at 40% oxygen until the cat was completely awake and oxygen saturation as determined by pulse oximetry was > 95%. Pain was controlled with methadone (0.3 mg/kg [0.14 mg/lb], IV, q 6 h). After extubation, the cat developed signs of dysphoria; therefore, dexmedetomidine (1 μg/kg, IV, once) was administered to provide sedation and alleviate the abnormal signs. In addition, enalapril (0.27 mg/kg [0.12 mg/lb], PO, q 24 h), furosemide (1 mg/kg, PO, q 12 h), and amoxicillin–clavulanate potassium (13.29 mg/kg [6.04 mg/lb], PO, q 12 h) were continued, but oxygen supplementation was discontinued 8 hours after surgery. The cat remained hospitalized for 3 days, and prior to discharge, pain control treatment was switched to buprenorphine (0.02 mg/kg [0.009 mg/lb], sublingual, q 8 h) and robenacoxib (1.2 mg/kg, PO, q 24 h for 3 days).

Two weeks after surgery (14 weeks after initial evaluation), the cat was returned for a recheck examination with the cardiologist. The owner reported that the cat was doing well at home and was no longer coughing. On examination, the cat's heart rate (192 beats/min) was within reference limits; however, the cat was mildly tachypneic (36 breaths/min). A grade 5/6 right apical systolic heart murmur was auscultated, and an indirect systolic blood pressure of 167 mm Hg was measured with a Doppler ultrasonic flow detector. Echocardiography was performed and revealed mild pulmonic stenosis (pulmonic valve peak velocity, 2.94 m/s; pressure gradient, 34.6 mm Hg); however, the maximum shunt velocity (5.48 m/s) had returned to near preoperative velocity (5.31 m/s). Therefore, dosages were lowered for both enalapril (0.19 mg/kg [0.086 mg/lb], PO, q 24 h) and furosemide (0.75 mg/kg [0.34 mg/lb], PO, q 48 h).

A month later (18 weeks after the initial evaluation), general anesthesia and orchiectomy were performed on the cat at the veterinary teaching hospital. No complications occurred, and medical treatment continued without change to the dosages of enalapril and furosemide.

At 14 months after pulmonary artery banding, the cat was returned for a recheck examination with the cardiologist. The owners reported that the cat was doing well at home and had no clinical signs related to congestive heart failure. Echocardiography revealed a Qp:Qs of 1.5, indicating a hemodynamically insignificant shunt, compared with the preoperative Qp:Qs value of 3. Medical treatment continued with enalapril (0.19 mg/kg, PO, q 24 h), and a plan was made to reduce the dosage of and eventually discontinue furosemide over the following 4 weeks.

Discussion

Ventricular septal defect is the most common congenital heart abnormality in cats.5 The defect can be located in the muscular septum, near or involving the ostium primum, in the membranous septum, or beneath the aortic valve,6 with perimembranous VSDs located within the membranous septum beneath the aortic valve being most common.7 Further, the defect most commonly results in left-to-right shunting of blood that increases the risk for overload of the pulmonary vasculature that could subsequently result in pulmonary hypertension and left ventricular enlargement.7 Ventricular septal defects can be categorized as restrictive or nonrestrictive. The term nonrestrictive implies that a substantial amount of blood flows from the left ventricle to the right ventricle, increasing venous return to the left side of the heart and potentially causing pulmonary hypertension.7 This overcirculation of the pulmonary vasculature tree and left side of the heart also increases the risk for left-sided congestive heart failure. Clinical signs suggestive of congestive heart failure include cough, dyspnea, tachypnea, signs of exercise intolerance, and a systolic heart murmur with a point of maximum intensity just right of the sternum.8 The term restrictive implies that the right ventricular systolic pressure is the same as the systolic pressure of the left ventricle. When pressures in both ventricles are the same, the left side of the heart is not at risk for overcirculation of the pulmonary vasculature.

Surgical treatment of VSD in humans and veterinary patients can be accomplished in multiple ways. In human medicine, definitive correction of a VSD can be accomplished by means of an open-heart surgical procedure, for which cardiopulmonary bypass is required; with a transcatheter closure procedure, which is technically challenging; or through percutaneous placement of an occluder device, which has more recently been described.9,10 Open-heart surgery has been linked to high patient morbidity rates, long durations of hospitalization, and high risks for the need of blood transfusions.9 In veterinary medicine, definitive correction of a VSD with open-heart surgery can be performed; however, this treatment option is rare because of the required cardiopulmonary bypass. More frequently, patients are treated medically or with palliative surgery involving pulmonary artery banding.6,8 During the banding procedure, the pulmonary artery trunk diameter is reduced by approximately 30%, increasing the blood pressure in the right ventricle and decreasing the systolic left-to-right pressure gradient and the amount of blood shunting between vetricles.11,12 Percutaneous transcatheter coil embolization of a VSD in a dog has been reported, and 3 months after placement of the coil, the patient was clinically normal.13 That technique has not been reported in a cat.

Case selection criteria for palliative pulmonary artery banding are largely undetermined; however, the decision to perform the procedure is generally reserved for cases in which the patient has clinical signs of left-sided heart failure that develop or persist despite treatment with diuretics and an angiotensin-converting enzyme inhibitor.7 The procedure can be performed in patients with large VSDs, but is contraindicated in patients with right-to-left shunting (Eisenmenger complex).7 Veterinary medicine does not have specific parameters for when to perform the surgery in veterinary patients; however, in human medicine, it is suggested that a patient with a Qp:Qs > 2.5 is a surgical candidate. Further, a Qp:Qs < 2 is reported as hemodynamically insignificant, meaning that it is unlikely to affect systemic oxygenation, whereas a Qp:Qs > 2 is reported as hemodynamically significant, meaning that it is likely to affect systemic oxygenation.14

We identified a lack of veterinary literature discussing palliative pulmonary artery banding for treatment of VSDs. Although use of the procedure was reported to have successfully treated a perimembranous VSD and patent ductus arteriosus in an 8-week-old kitten, banding was performed with a polymeric silicone band, and the role of pulmonary artery banding in the patient's clinical improvement could not fully be assessed because the kitten's patent ductus arteriosus was ligated at the same time.15 Success of the treatment in the kitten was identified by an increase in left ventricular fractional shortening (a measurement of left ventricular function) and an increase in transventricular pressure 12 months after surgery.15 An older study11 reported successful pulmonary banding with umbilical tape in 4 dogs and 1 cat, for which follow-up time ranged from 5 to 7 years, but lacked objective echocardiographic data supporting improvement. Success in those patients was defined by improvement in their coughs.

To our knowledge, the present report was the first to document long-term follow-up (14 months) and a direct association between pulmonary artery banding and cardiovascular improvement for a cat with a VSD. The Qp:Qs conferred important physiologic information about the magnitude of a left-to-right shunt, and in the cat of this report, the Qp:Qs decreased from 3 (indicating a hemodynamically significant shunt) before surgery to 1.5 (indicating a hemodynamically significant shunt) after surgery. Given the outcome of the cat in the present report, combined with our review of the human medical literature, we think that the pulmonary artery banding procedure could be considered as a treatment option for cats with a VSD and Qp:Qs > 3 or that have congestive heart failure as a result of the VSD.

The intraoperative decrease in VSD shunt velocity was likely related to the effects of anesthesia in that isoflurane could have been responsible for systemic hypotension and thus could have confounded direct blood pressure measurements obtained from the pulmonary artery during surgery. In addition, malalignment of the transducer probe during transcardiac echocardiography could have resulted in falsely low measurements of velocity; however, efforts for accurate alignment were made.

Although at 2 weeks after surgery, the shunt velocity had not decreased from the velocity recorded before surgery, the cat had developed mild pulmonic stenosis, which is a goal of pulmonary artery banding because pulmonic stenosis helps raise the pressure in the right ventricle and lower the pressure gradient across the ventricles. Therefore, cats with a VSD and a Qp:Qs > 3 or congestive heart failure should be considered as candidates for palliative pulmonary artery banding to alleviate clinical signs. Further veterinary medical investigation into long-term prognosis with objective outcome measurements and with multiple cases is needed.

ABBREVIATIONS

PTFE

Polytetrafluoroethylene

Qp:Qs

Pulmonary blood flow-to-systemic blood flow ratio

VSD

Ventricular septal defect

Footnotes

a

Plasma-Lyte, Baxter Healthcare, Deerfield, Ill.

b

Gore-Tex Soft Tissue Patch, W. L. Gore & Associates Inc, Flagstaff, Ariz.

c

Bard PFTE felt pledgets, Medline Industries Inc, Mundelein, Ill.

d

VetTrends V plus vital signs monitor, VetTrends, Tampa, Fla.

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