We retrospectively analysed nine dogs that had been treated consecutively at the Nihon University Animal Medical Center between 2006 and 2009. Data were retrospectively collected by reviewing the medical records, including clinical signs and postoperative course.
A diagnosis of pulmonic stenosis had been established in all nine dogs by physical examination, ECG, radiography, and two-dimensional and Doppler echocardiography. Doppler measurement of the systolic pressure gradient across the pulmonary valve was assessed by the modified Bernoulli equation. According to the pressure gradient, dogs were classified into the following categories: mild stenosis, 10 to 49 mmHg; moderate stenosis, 50 to 80 mmHg; and severe stenosis, more than 80 mmHg (Bussadori and others 2001). The decision to apply surgical palliation for pulmonic stenosis was made based on the severity of the pressure gradient, the presence of moderate to severe right ventricular hypertrophy and/or clinical signs.
The type of valvular stenosis (type A or B) was classified based on the results of echocardiography, as well as direct visual observation of the valve leaflets during surgery. Type A was diagnosed when mild to moderately thickened leaflets was observed, with evidence of commissural fusion and systolic doming. Type B was diagnosed when severely thickened leaflets were observed (Locatelli and others 2011).
Doppler echocardiography studies were repeated at various times for each case at 1 to 7 days, 1 to 3 months and at 6 months to 3 years postoperatively. A single echocardiographer (MU) consistently performed all the measurements, thus precluding interobserver variability.
Anaesthesia and surgery
The dogs were anaesthetised using 0·025 mg/mL, im atropine sulphate premedication (atropine sulphate injection®; Mitsubishi Tanabe Pharma Corporation), 0·1 mg/kg, iv, fentanyl (Fentanyl®; Daiichi Sankyo Company), 0·2 mg/kg, iv, midazolam (Dormicum®; Astellas Pharma Inc.) and 20 mg/kg, iv, cefazolin sodium (Cefamezin®; Astellas Pharma Inc.). Anaesthesia was induced in each dog with 5 μg/kg, iv, fentanyl and 4 mg/kg, iv, propofol (Rapinovet®; Schering-Plough Corporation) and maintained by inhalation of 1·5 to 2·5% isoflurane and 100% oxygen (2·0 l/min). Respiration was maintained at 12 breaths/min with 100% O2 using a ventilator (7900 SmartVent™; GE Yokogawa Medical Systems Ltd).
During CPB, anaesthesia was maintained by 0·4 μg/kg/min, iv, fentanyl and 0·2 mg/kg/min, iv, propofol. During the operation, the left femoral artery and vein were catheterised for time-lapse measurements of arterial (systolic, diastolic and mean) and central venous pressures. Heart rate, arterial oxygen saturation, end-tidal CO2, isoflurane concentration, rectal temperature and oesophageal temperature were continuously monitored. The volume of urine was also monitored by a catheter in the bladder.
Cardiopulmonary bypass was provided by a heart-lung machine (NAPS-III®; Senko Medical Instrument), with a small extracorporeal circuit (Terumo), oxygenator and heat exchanger (Baby-RX®; Terumo). The CPB circuit was primed with 5 mL/kg d-mannitol (20% Mannitol®; Kowa Company), 2 mL/kg sodium bicarbonate (7% Meylon®; Otsuka Pharmaceutical Factory, Inc.), 500 U/head heparin sodium (Novo-Heparin®; Mochida Pharmaceutical Co.) and Ringer’s acetate solution (Veen-F®; Kowa Company). Fifty millilitres of whole blood was replaced with priming solution in dogs weighing less than 4 kg.
Thoracotomy was performed with a median sternotomy in case 1. In the other eight cases, thoracotomy was performed through the fourth intercostal space after an intercostal nerve block with bupivacaine hydrochloride (Marcain®; Astrazeneca).
A measure of 400 U/kg heparin sodium was administered, and the activated clotting time (ACT) was measured to confirm that it was ≥300 seconds prior to CPB cannulation. The CPB cannula was inserted into the carotid artery, and the jugular vein was cannulated for venous return in all cases. In cases 1 to 3, the vena cava was also cannulated through the right atrium. Then, partial CPB was initiated. The blood flow was set at 100 mL/kg/min by the extracorporeal circulation pump. Oesophageal and rectal temperatures were monitored. Each dog was cooled to a rectal temperature of 25 to 28°C.
In cases 1 to 3, after the aorta was occluded using an arterial clamp, 10 mg/kg cardioplegic solution (Miotecter®; Mochida Pharmaceutical Co.; cooled to ≤4°C, Na+: 120 mEq/L, K+: 20 mEq/L, Cl–: 160·4 mEq/L, Mg2+: 32·0 mEq/L, Ca2+: 2·4 mEq/L, HCO–: 10 mEq/L) was immediately and rapidly infused into the coronary artery via a catheter extended into the root of the aorta. A measure of 10 mL/kg cardioplegic solution was administered every 20 minutes.
In cases 4 to 9, intracardiac procedures were performed on the beating heart. The reservoir blood level was constantly maintained at a stable level during the pulmonary artery procedure to prevent “air block”.
In case 1, a polytetrafluoroethylene (PTFE) patch was placed along the atrial septal defect (ASD) and secured by a simple continuous suture with 6-0 Prolene sutures (Proline® 8725H; ETHICON). Immediately after the complete closure of the ASD, the right atrium was sutured. Since echocardiography confirmed that ASD was mild in case 2, it was not treated. Once the main pulmonary artery incision was made, the hypoplastic valve was identified and the thickened or fused leaflet was resected with scissors. The reduction in the stenosis was confirmed by passing an inflated tracheal tube, which had a diameter equivalent to that of the pulmonary artery, from the main pulmonary artery through the pulmonary valve.
In cases 2 and 3, a patch graft was affixed over the right ventricular outflow tract, using continuous 6-0 Prolene sutures, to dilate the lumen; for this purpose, we used biomaterial allografts, i.e., glutaraldehyde-fixed canine tunica vaginalis obtained at the time of castration. In the seven other cases, the pulmonary artery incision was sutured with continuous 6-0 Prolene sutures. When haemostasis was required during suturing on the pulmonary artery, bovine dermis-derived atelocollagen (Integran®; Nippon Zoki Pharmaceutical Co.), which is an absorbable local haemostat, was used.
In case 1, perioperative defibrillation was required (Defibrillator FC-1760, Fukuda Denshi), and resulted in the sinus rhythm returning immediately.
After the CPB pump was stopped, 6 mg/kg protamine sulphate (Novo-Protamine Sulfate®; Mochida Pharmaceutical) was administered by slow iv injection. After the ACT was reduced to less than 200 seconds, a thoracic tube was put in place prior to chest closure, and the cervical wound was closed routinely.
Postoperative management was conducted in the intensive care unit. Air and fluid in the thoracic cavity were removed through the thoracic tube. Antibiotics, 20 mg/kg, iv (Cefamezina®; Astellas Pharma Inc. ) every 8 hours were administered for 1 week. The dogs were discharged from the hospital 3 to 11 days postoperatively.
Friedman’s test was used to assess differences in the pressure gradient preoperatively and at 1 to 7 days, 1 to 3 months, and 6 months to 3 years postoperatively. A P-value of less than 0·05 was considered statistically significant.