This is not a simple surgical procedure. It is a complete and complex medical-surgical procedure from the preoperative phase to the hospital discharge 7 days later, where a team of 10 veterinarians intervenes for a single dog. Each veterinarian has a specific role, either medical or surgical. The procedure requires 2 surgeons (surgeon and one assistant surgeon), 3 sterile instrumentalists, 3 non-sterile assistants, 1 perfusionist, 1 anesthetist-resuscitator, and 1 cardiologist sonographer.
“The success of this intervention is due to the perfect harmony of a team that is united and perfectly in sync where everyone has his or her role and no technical or biological details are left to chance. Absolutely everything is under control.” -- Dr. Sabine Bozon
The “master machine” that makes open heart surgery possible is called the Cardio-Pulmonary Bypass (CPB) Machine. In addition to this machine, the intervention requires 2 anesthetic machines - one with assisted ventilation (isoflurane or sevoflurane), a monitor to show live vital statistics, a thermal generator which cools or reheats the animal’s body on request at a precise temperature, a surgical table inclinable in all directions, an echograph with color doppler and a pediatric transesophageal probe, 4 syringe pumps and 2 infusion pumps, a coagulation time measuring device, a blood gas analyzer, a blood-biochemical analyzer, an electrolyte analyzer, an internal pediatric pallet defibrillator, a pace-maker, fresh blood compatible for transfusion (a machine called “cell-saver” in order to recycle the lost blood and carry out autotransfusions), a cardioplegic solution (which stops the heart), frozen sterile physiological serum, a large number of consumables and injectable medicines, conventional surgical aspirator equipment, a fine-tuned electric scalpel, microsurgical instruments, customized equipment (catheter, tubing, etc…) and more.
“This is one of the biggest constraints of the intervention for small breeds,” says Dr. Sabine Bozon. She continues, “we are able to operate on chihuahuas weighing 2kg or less. Instead, extracorporeal circulation techniques have been attempted in some medium or large sized dogs where traditional techniques used in pediatric surgery may possible be reproduced in dogs.”
In dogs of any small size, difficulties are encountered given the low initial circulating blood volume. Dr. Uechi has succeeded in developing an extracorporeal circulation procedure that does not use traditional techniques, and allows the operation of miniature dogs and even cats. The use of extra-corporeal circulation can induce cardiac arrest and therefore work freely for the time required during the surgical open heart repair.
The CPB machine allows the heart and lungs to be taken over during surgery and requires: 3 pumps (one of which is equivalent to the heart pump), a system for mixing and exchanging blood cases (oxygenator, equivalent to the lungs), a system for controlling blood and body temperature (thermal generator), a tubing system adapted to the conformation of the dog. The mastery of extracorporeal circulation by the perfusionist is crucial to the success of the intervention.
Dr. Sabine Bozon and her husband, Dr. Jean-Hugues Bozon are currently the only vets in Europe with a degree in extracorporeal circulation sciences. Their goal is to teach this brand new topic in veterinary medicine in different countries to improve the way we treat dogs. Mastering extracorporeal circulation is the future in terms of treatment of heart disease in dogs.
Steps of the Surgery
Prior to the induction of general anesthesia, the maximum number of steps is performed on animal vigil: insertion of 2 intravenous catheters (typically in anterior limbs), insertion of a urinary catheter (Foley catheter), shaving the left cervical area, the entire left chest wall, and the medial right posterior limb. The operating room is also prepared during this phase.
Surgical placement of an arterial catheter and venous catheter to measure invasive arterial blood pressure and central venous pressure throughout the procedure and especially during cardiotomy (heart stopping phase, approximately 2 hours).
Surgical opening of the rib cage, reclination of the lungs, pericardiectomy and access to the heart.
Dissection of the base of the aorta and minimal separation of the aorta and the pulmonary artery.
Administration of intravenous bolus heparin to induce a non-coagulable state. For this purpose, measurements of the activated partial thromboplastin time (ACT) are carried out until a minimum value of 300 seconds is obtained.
Laying of extracorporeal circulation cannulas. The left carotid artery and jugular vein are surgically isolated and a cannula is inserted into each vessel, their size depending on the type of cannulated vessel and the body weight of the dog.
Implementation of the partial and then total extracorporeal circulation. The cannulas are connected to the extracorporeal circulation circuit after carefully evacuating the air bubbles from the tubing. The arterial and venous lines are unclamped and the CPB starts at the adapted rate.
Transesophageal ultrasound: a pediatric transesophageal tube connected to an echocardiograph equipped with color flow doppler is inserted delicately in order to successfully obtain the median transverse and longitudinal views. The movement of the mitral leaflets and regurgitation are examined by the surgeon.
Catheterization of the ascending aorta (installation of the cardioplegia cannula): a catheter is gently inserted on the left lateral face of the ascending aorta.
Decreased body temperature: the body temperature is gradually decreased up to 28 degrees and maintained thanks to the thermal generator integrated in the extracorporeal circulation machine.
Injection of cardioplegic solution (via blood cardioplegia) in the coronary arteries via the aortic catheter and induction of cardiac arrest.
Incision of the left atrium and placement of the aspirations cannulas.
- Pre-placement of artificial cordages: replacement of mitral tendon cords is the best technique for repairing broken cords. Double sutures of expanded polytetrafluoroethylene (e-PTFE or Gore-Tex) are placed between the papillary muscles (reinforced by pledgets to avoid tearing of the papillary muscle) and the mitral leaflets. Depending on the dog, a total of 4 to 6 new cords are laid.
- Mitral annuloplasty: tightens the mitral ring in order to decrease or even cancel the mitral regurgitation and thus to maintain a good systolic coaptation. The same material as the cords is used (ePTFE) in the form of two sutures reinforced by pledgets at the level of each commissure of the mitral ring.
Tightening of the replacement cords: the main challenge here is the difficulty in adjusting the cords, in length and tension, in order to obtain the optimum coaptation when closing the mitral valve. This phase is highly dependent on the surgeon’s experience and the mitral valve leaflets echostructure. The result is then tested with physiological serum under pressure in the left ventricular chamber by tilting the table.
Suture of the left atrium, evacuation of the intra-atrial air under transesophageal ultrasound control and declamping of the aorta.
Restarting the heartbeat: upon cessation of intracoronary administration of the cardioplegic solution, heartbeats are expected to resume spontaneously. A direct cardiac massage is performed systematically and if the heart does not restart on its own, a temporary pacemaker is placed or ventricular defibrillation is undertaken.
Transesophageal ultrasound recheck: the coaptation of the mitral leaflets and the mitral regurgitation are appreciated, which has usually decreased by at least 80%.
- Progressive temperature rise in the body of the animal and gradual decrease in the flow rate of the arterial pump.
Removal of the carotid and jugular cannulas and termination of the CPB.
Continuous perfusion of protamine (heparin antagonist) over a 20-minute period. Simultaneous administration of continuous dobutamine infusion if invasive blood pressure is too low and unstable. Indeed, protamine can cause severe hypotension, bronchospasm and increased pulmonary vascular resistance. Ventilation and blood pressure should therefore be perfectly controlled at this time.
Closure of the thorax plane by plane (the pericardium is not sutured).
Chest tube placement.
Progressive waking over 2-3 hours: During this crucial phase, all the vital parameters and ventilation are closely controlled and their return to normal are obtained very gradually. Femoral catheters will be removed just before the actual wake-up (isoflurane stop) once invasive systolic blood pressure remains stable. The dog is then placed in an intensive care cage with oxygen supply and regulation of the ambient temperature as well as hygrometry.
Postoperative Care and Prognosis
Once the mitral valve is repaired and the new cords are laid, the mitral prolapse improves, the coaptation of the leaflets are almost normalized and the mitral regurgitation is decreased by at least 80% in most dogs. There is incredible plasticity of the left atrium which has the ability to shrink back to its normal size in less than a week if the quality of the muscle allows. On the other hand, the treatment for heart failure is either stopped the day after the intervention or gradually over a month. Some dogs require treatment if the repair has been difficult, however most only require blood thinners prescribed for 3 months. This is to prevent thromboembolism (blood clotting), the most frequent complication seen postoperatively, the maximal risk being between the 1st and 4th days after surgery but can last longer especially in Cavalier King Charles Spaniels. Some cases of acute pancreatitis are also seen postoperatively, follow-up of specific pancreatic lipase is recommended during the week of hospitalization. A systemic inflammatory syndrome is more or less always present and must be managed, as best as possible.
After the procedure, “the vast majority of dogs recover a life of an asymptomatic dog in B1 stage heart failure requiring almost no treatment for congestive heart failure, including furosemide for most of them, even if they were in stage D before surgery.”
Consequently, dogs who have received surgical intervention no longer suffer from respiratory problems, regain the possibility of exerting effort, regain appetite, regrow, or no longer suffer from kidney failure. If treatment persists, it is sildenafil which is still necessary in half of the dogs who had pulmonary arterial hypertension prior to surgery.
Dr. Sabine Bozon says that it is possible to operate at any age, but before 13 years is ideal. A complete medical and biological check-up must be carried out before each intervention so that no concomitant illness will cloud the prognosis. The surgical procedure (induction of anesthesia until closure of the thorax) lasts from 4 to 8 hours depending on the complexity of the case. Then, in addition, 2 hours of preparation of the materials and the dog before anesthesia and 3 hours of progressive awakening after the thorax is closed. The entire procedure end-to-end lasts 9 to 13 hours, depending on the case.
Hospitalization is required for 1 week after surgery. A thoracic drain is placed at the end of surgery and removed the next day. The dog can stand the day after surgery and can take water and eat a little. A continuous infusion of Fentanyl (pain medication similar to Morphine) is administered the day of and the day after surgery unless needed longer. The surgery is not painful. During the week of hospitalization, dogs are monitored hourly and vital parameters are tracked, solid food is administered, echocardiogram and doppler are performed at least once daily. Ventricular arrhythmias are frequent in the first postoperative days. They very rarely require treatment and disappear spontaneously and gradually during the first week.
The dog regains a normal life a week after surgery, is only allowed to go out for brief, slow walks for a month, and modified resumption of physical exercise is allowed after 3 months. Please see this article posted about post-operative physical activity recommendations for more information.
Mitral Valve Surgical Treatment Corrects a Mechanical Defect
Surgical treatment represents a life-long curative treatment since it corrects the mechanical defect while medical treatment can only mitigate the negative consequences of mitral regurgitation. The surgical technique was developed over 10 years ago at the Tokyo Veterinary University by Dr. Masami Uechi. This technique reduces the diameter of the mitral ring, called annuloplasty, to significantly reduce mitral regurgitation and replaces cords to avoid mitral valve prolapse. This surgery is still carried out to date with a success rate of about 90%.
“Dr. Uechi is the most experienced in the world today, and has already operated on over 600 dogs. His strength is his ability to be both a doctor and a surgeon. He began his career as a professor of internal medicine in cardiology and nephrology. Then, seeing that many of the dogs dying from kidney failure were in fact dogs suffering from heart failure under high doses of furosemide (a diuretic commonly known as Lasix in the United States), he directed his research towards surgical cardiology. Frustrated with so few results with medical treatments, he decided to tackle this cause relentlessly: repair the degenerative mitral valve and broken tendon cords. The goal is to wean the dogs from their medical treatment and lengthen their lifespan to their life expectancy inherent to their breed.” -- Dr. Sabine Bozon
Still surrounded by a few students who were part of his initial team, Dr. Uechi, an internist, has gradually become a surgeon and succeeded in finalizing this procedure in 7 years before publishing in The Journal of Veterinary Cardiology in 2012, once he obtained a satisfactory rate of success. As the leader of the medical and surgical procedure, he has built and educated a team of veterinarians performing well where each performs his role to perfection. Its great strength is the mastery of each specialty: extracorporeal circulation (crucial point), anesthesia and resuscitation techniques, monitoring and postoperative intensive care, cardiology, doppler echocardiography, and finally the surgical technique.
Faced with the success of his new procedure, Dr. Uechi has now left university and is practicing in Japan exclusively in a private hospital with his team of veterinarians, in a referral structure specifically dedicated to cardiac surgery under extracorporeal circulation. All of this progress has been made by one man.
In a Decade, a “Routine” Intervention
For now, the help and presence of the Japanese is essential for at least 6 years for this intervention, it is not experimentation. Dr. Jean-Hugues Bozon (surgeon) and Dr. Sabine Bozon (cardiologist) have been learning this surgical technique from Dr. Uechi himself since 2012. They both hold a medical degree in Cardio-Pulmonary Bypass Sciences, which is essential to be able to perform this procedure. Many topics within this degree have to be covered: cardiology, extracorporeal circulation, surgery as an instrumentalist, surgery as a 1st assistant, anesthesiology, intensive care, and internal medicine, among others. The surgical technique itself also takes a long time to learn.
Dr. Uechi is currently the only one to be able to successfully make a hand-made repair of the mitral valve during the crucial phase of cardiac arrest. Dr. Jean-Hughes and Dr. Sabine are both training in human cardiac surgery as well to witness the procedure. Not many human cardiac surgeons use the repair technique which is the gold-standard treatment as it lasts for life. They would rather use the mitral valve replacement technique, which lasts for only approximately 10 years, by suturing a pre-prepared annulus which is much easier and faster to perform than the made-to-measure repair. In small breed dogs, it is even more difficult technically speaking and, unfortunately, a replacement is impossible in dogs because they do not have the same coagulation system as humans and such a small size artificial annulus does not exist.
Dr. Sabine Bozon highlights the importance is selection criteria. All dogs are “technically” operable, but many criteria must be taken into account before proposing the intervention to an owner and to advise him what percentage of success that he may have before accepting or not. It is also important to leave time for reflection, as it is a significant psychological and financial investment. Nevertheless, this new procedure is a real revolution in the treatment of canine heart disease which will certainly be carried out routinely in the next 10 years in some specialized centers. All means must be implemented to achieve the highest possible success rate. For this, the conditions must be optimal at the human and technical level. Nothing should be left to chance.
All information and photos provided by and with the express permission of Dr. Sabine Bozon, Clinique Veterinaire Bozon.