An EPIC Change in the Management of Mitral Valve Disease in Dogs
Sarah Clay Bell, DVM, MS, DACVIM-Cardiology
For years, there has been great controversy about the management of canine degenerative mitral valve disease (DMVD). Data from the SVEP and VETPROOF trials offered insight but also conflicting results in regards to the use of ACE inhibitor therapy for dogs with DMVD. Even within the ACVIM consensus statement, no consensus could be found in the treatment of patients with stage B2 disease. Some clinicians argued for treatment with vasodilator therapy while some did not recommend any treatment until a patient would go into congestive heart failure.
|Stage A||Patients at high risk for developing heart disease but without current identifiable structural disorders (e.g. cavalier King Charles spaniel without a heart murmur).|
|Stage B||Patients with structural heart disease that have not developed clinical signs caused by heart failure.|
|Stage C||Patients with past or current clinical signs of heart failure associated with structural heart disease. May or may not require hospitalization and aggressive anti-congestive therapy.|
|Stage D||Patients with end-stage disease with clinical signs of heart failure caused by CVHD that are refractory to “standard therapy” (defined later). Such patients may require advanced or specialized treatment strategies in order to remain clinically comfortable (quality of life). May or may not require hospitalization and aggressive anti-congestive therapy|
At the 2016 ACVIM Forum in Denver Colorado, the results of the EPIC trial (Evaluation of Pimobendan In Cardiomegaly) were presented. The dogs in this study were small breeds with confirmed DMVD. The patient population had signs of significant cardiomegaly based on the results of radiographs and echocardiographic data, specifically the following criteria:
- Left atrial:aortic ratio>1.6
- LVEDDN >1.7 (left ventricular dimension in diastole normalized to body weight)
Results of the study demonstrated that pimobendan delayed the onset of congestive heart failure by about 15 months as compared to placebo. The results of this study demonstrated that pimobendan had great monotherapy benefit to delay the onset of heart failure in small dogs with stage B2 DMVD.
Questions still remain as to how pimobendan would perform as compared to an ACE inhibitor like enalapril or benazepril or whether a combination of pimobendan with an ACE inhibitor would be superior. There is also some question on what influence pimobendan has on the risk of sudden cardiac death. In the EPIC study group, the incidence of sudden death was greater in the pimobendan treated group vs. the placebo group. This may, however, have been a function of the longer asymptomatic period. A small study in the past has shown progressive histopathologic changes to the mitral valve in dogs with experimentally induced mitral valve regurgitation when treated with pimobendan. Thus, very early use of this agent in patients with valve disease can have the potential for detrimental effects as well.
Based on the data from this landmark study, it appears that pimobendan should be utilized in the treatment of patients with advanced stage B2 degenerative mitral valve disease prior to the onset of heart failure. Treatment is not recommended until a complete physical examination, blood profiles, blood pressures, chest radiographs and thorough echocardiographic studies are performed to confirm that significant enough disease is present to warrant treatment. The EPIC data supports the use of pimobendan once signs of significant left atrial and left ventricular dilation are present, but not when the heart size is normal or even mildly enlarged. Whether better results are possible with pimobendan used in combination with other medications is still a question. The EPIC trial was a well-designed study and will change the way we treat patients with degenerative valve disease.
Our Louisville hospital now offers cardiology services provided by CVCA Cardiac Care for Pets. If you have any questions, you can reach Dr. Bell at 502.410.0034
Patient Monitoring: Temperature
Despite all the technology, there are patient parameters that still be need to closely monitored. The simplest one is the patient’s temperature. How harmful can a low temperature be? After all, the patient will warm up after the procedure. Well not so fast. Body temperature is very important.
Most chemical reactions that occur in the body require an optimum temperature. To survive, the body relies on these chemical reactions, such as those responsible for ensuring nerve conduction as well as those required to maintain muscular and respiratory function, cell membrane health and even blood clotting. As the body temperature drops, metabolic processes in the body slow down. Cardiovascular function is adversely affected resulting in a drop in blood pressure and a slowing of the heart rate. Cardiac output and blood perfusion to the tissues becomes compromised depriving internal organs of the nutrients and oxygen they require to function properly. Gastrointestinal motility slows. The metabolism and excretion of anesthetic agents becomes delayed, prolonging the sedation. A low body temperature is a common reason for excessively prolonged recovery in anesthetized patients. As the body temperature continues to drop it becomes more difficult to reverse the trend as metabolic processes start shutting down.
Why does the body temperature drop in anesthetized patients?
There are numerous reasons for a drop in body temperature. Anesthetics inhibit muscular activity, especially the shivering reflex, and metabolic processes which are primarily responsible for heat production within the body. Furthermore, many anesthetics cause vasodilation increasing blood flow to the body surface where heat can be more rapidly lost from the body. Anesthetized patients can’t seek out a warmer environment or assume a curled posture to stay warm. Heat is also lost when a body cavity, such as the abdomen, is surgically opened exposing the warmer internal organs to room temperatures. Lavaging the abdomen with cool fluids only worsens the heat loss.
Optimum body temperature for our patients approximates 101o F whereas room temperature approximates 74o F. When we interfere with processes responsible for heat production and heat conservation, the body temperature will immediately start dropping toward 74o F. Studies have demonstrated that an anesthetized patient can lose up to 10o F (6 o C) during a 120 minute procedure. The smaller the patient the more rapidly the temperature drops. The longer the anesthetic procedure the more body heat is lost.
Keeping Them Warm
It is a lot easier to maintain the patient’s body temperature than try to raise it after it has dropped. This is because a drop in body temperature causes the body to shunt its blood supply to the internal organs away from skin to conserve heat. The application of external heat is therefore not initially transferred to the blood stream where it will be delivered to the rest of the body. With the continued application of external heat, peripheral vasodilation will start to occur. Blood will start to flow to the peripheral tissues of the body which are still much colder than tissues within the body core. Cooler blood flowing from the peripheral tissues will cause the core body temperature to drop further until these peripheral tissues can be more thoroughly warmed.
It is advantageous to not let the patient’s body temperature drop. Numerous tools and techniques are available to help maintain a satisfactory body temperature in anesthetized and postanesthetic patients. These include:
- Placing a warm water circulating blanket under the patient
- Wrapping the body in warmed radiant fabrics (HotDog˚® warming device)
- Using devices which blow warmed air into an air blanket that has been wrapped around the patient (Bair Hugger™)
- Covering with towels and blankets parts of the body which don’t need to be exposed
- Wrapping the extremities with plastic wrap or fabric
- Warming the IV fluids
- Using only warmed fluids for abdominal lavages
Caution should be taken if you are using warm water bottles, electric heating blankets, solar lamps and microwaved rice bags. These items are more likely to cause accidental thermal burns to the skin if they are too hot and not buffered by the presence of a towel placed between the heat source and the skin. Skin burns are more likely to occur in anesthetized patients because they cannot move away from excessive heat. In addition, peripheral vasoconstriction present in patients with low body temperatures does not allow for blood flow to the area to wick away the local heat. Burns are more likely to occur in areas of thin skin and those that lack insulation from hair.
It is also important not to overheat the patient. External warming steps should be reduced once the body temperature reaches the low normal range. The body temperature in these patients should continue to be monitored to make certain it does not drop again. If the patient’s temperature begins to fall during or after the recovery period the veterinarian should be alerted.
Leptospirosis: A Growing Concern for Urban and Suburban Dogs
No longer primarily a concern for country and hunting dogs, leptospirosis is a now a big threat for suburban and urban canine populations as well. Factors such as wildlife adaptability to our urban landscapes and a dog’s uncanny ability to find a puddle of standing water to drink from, have dramatically increased the rate of confirmed cases in the US in recent years. Leptospirosis (lepto for short) is a deadly bacterial disease spread via the urine of infected wildlife, and it can persist in standing water or wet grass for long periods of time. If diagnosed early, this bacterial infection is easily treated with a course of antibiotics. Unfortunately, the initial symptoms of lepto can be vague, and by the time the patient is noticeably ill, the bacteria may have already begun to damage the patient’s liver and kidneys. Treatment for the later stages of disease is possible, but can be costly. Lepto is not discriminatory to canine size or breed and is also zoonotic. Any dog that steps outside is at risk for contracting this disease. It can be as simple as sniffing wet grass, licking a puddle or wading in standing water.
The prevalence of leptospirosis in the urban and suburban environments has greatly increased in the past five years. Some risks include:
- Wildlife such as squirrels, skunks and deer are potential vectors of leptospirosis, with raccoons and rats being the main threat to our urban canine population.
- Infected wildlife can appear healthy, though actively shedding the bacteria through their urine, as symptoms are often subclinical.
- Lepto can persist in wet soil and stagnant water for long periods of time.
- Common routes of transmission are mucous membranes, open skin or ingestion.
- Lepto is zoonotic: Increase risk to our canine patients = increased risk to owners
- Increased risk in areas of floods
- There is a greater risk associated with the changing of seasons, such as the beginning and end of winter, when wildlife activity increases.
- Any dog that goes outside is at risk of contracting lepto.
- Once contracted, the lepto bacteria will begin multiplying within the blood ~ 1 day
- Rapid replication occurs within the next few consecutive days
- Symptoms occur within 3-7 days after infection.
- Target organs of the lepto bacteria include (but are not limited to) liver, kidneys, lungs, endothelium, central nervous system, eyes, reproductive organs
- Clinical symptoms are usually vague and non-specific, such as fever, lethargy, generalized pain, icteric, pu/pd, anorexia, vomiting, coughing, uveitis and dehydration
- Clinicopathologic findings can include:
- Azotemia, liver enzyme abnormalities, hyperbilirubinemia
- Leukocytosis, thrombocytopenia
- Coagulation defects
- Imaging such as thoracic radiographs and abdominal ultrasound
- Referral to your local BluePearl internal medicine team
- Supportive care
- Organ specific treatment
- Penicillin-derivatives and doxycycline both terminate bacteremic stage and sterilize urine. Penicillins are the treatment of choice in the acute stage of infection. Doxycyline terminates carrier states.
- Fluid therapy (sometimes in high rates due to polyuric state) with electrolytes
- Referral to your local BluePearl internal medicine team, if necessary
Veterinarians and staff should always wear gloves, mask and protective eye wear when handling the suspected or confirmed cases. Infected patients will actively shed live bacteria for up to two days after antibiotic treatment has begun. Place a urinary catheter if urine is contaminating hospital and use bleach for cleaning. For outside voiding, do so away from other dogs and in a bright, sunny spot.
There is an effective vaccination for lepto available. Our specialists at BluePearl Veterinary Partners highly recommend annual vaccination by the primary care clinician. It is the most affordable way to protect your clients’ pets from a disease that can be very costly to treat. Inform clients on the risks of lepto and how to take certain precautions, such as minimizing wildlife activity in yards and discouraging pets from drinking from or wading in stagnant water.
Negative Pressure Wound Therapy (NPWT):
A Better Solution for Complex Wounds
Wounds are a common cause of morbidity in our patients, and management of complex wounds can be prolonged and debilitating, leading to long hospital stays, painful and labor-intensive bandaging, and significant financial hardship. The most successful wound care plan takes into consideration all of the components of a wound (depth, degree of contamination, size, location, chronicity) as well as the clinical presentation of the patient (systemic health, personality, age). We have come a long way from the time of the wet-to-dry bandage, and today there are a number of moist wound care products to choose from that follow the typical course of healing through inflammation, proliferation, and finally maturation.
Negative pressure wound therapy (NPWT) is a wound healing modality that intervenes at the proliferation stage of healing and has some pretty amazing results. Functionally, NPWT is the application of subatmospheric pressure to a wound bed, open or closed, through foam dressing. This results in decreased interstitial edema, reduced bacterial load, the creation of a closed environment, improved circulation and enhanced granulation bed formation. While there’s never only one way to treat a wound, I have found that in some cases NPWT is the most efficient path to resolution. Faster granulation bed formation means fewer trips to the hospital, fewer bandage changes and often sets the stage for earlier delayed primary closure.
Nuts and bolts of bandage application
NPWT bandages have to be applied at the right time to the right wounds. They have no part in the debridement phase of a dirty, devitalized or infected wound. After adequate debridement (that may take several days), the bandage is applied. This consists of open cell foam covered by adaptic dressing placed within the wound bed. Skin edges can be advanced to the foam edges as determined by the wound configuration. Adhesive drape material covers the entire dressing and tubing that connects the foam to a vacuum pump and collection reservoir. Negative 125 mmHg is an adequate setting for most applications, and the bandage can stay in place for up to 72 hours. Most commonly, NPWT therapy is used for 3 to 6 days, but the bandage is often only changed once under moderate sedation. This results in a hospitalized patient who needs less sedation or anesthesia, gets more consistent nutrition, and is more comfortable and amenable to treatment.
Photo 1: Placement of foam dressing within a septic incisional dehiscence wound
Photo 2: After placement of tubing and adhesive dressing
Photo 3: After 6 days of NPWT
Photo 4: Closure
Photo 1: Multiple wounds, such as these bite wounds, can be treated in one bandage.
Photo 2: Foam bridges connect wound dressings.
Photo 3: After placement of the adhesive
Photo 4: Patients are comfortable with the NPWT bandage in place.
How does it work?
The application of uniform negative pressure to a wound bed removes from the area interstitial fluid that contains high levels of inflammatory cytokines and proteases in chronic wounds. It also helps to decrease the local pressure which can increase perfusion pressure and restore blood flow to previously collapsed capillaries and lymphatics.1 Negative pressure also has a direct effect on blood vessels by increasing vascular diameter and blood velocity and by initiating earlier angiogenesis – within the first hours of the application of negative pressure.2,3 Negative pressure also deforms tissue by deforming the skin edges and limiting the loss of domain that happens when wound edges naturally retract. On a microscopic level, the mechanical force of microdeformation has a fundamental role in regulating tissue growth by placing traction on the extracellular matrix and thereby turning on growth factors that regulate cellular proliferation.4 This is similar to the Ilizarov technique of distraction osteogenesis, which is based on the principal that tissue, in this case bone, responds to mechanical tension. Finally, NPWT stabilizes the wound environment by creating a semipermeable membrane that keeps ongoing contamination out, provides an appropriate electrolyte balance, and maintains body temperature. Under these conditions and through these mechanisms, granulation tissue forms more quickly.
NPWT was developed for humans to treat diabetic ulcers and open fractures. Since its inception over 500 peer-reviewed articles have been published in the human literature reporting its efficacy. Veterinarians have adapted the use of NPWT to our patients over the past 15 or so years, but evidence of efficacy is sporadic. Excellent evidence supports the use of NPWT in early treatment of distal extremity shearing wounds5 and to stabilize full thickness skin grafts.6 It was confirmed to speed the formation of smooth, nonexuberant granulation tissue in acute wounds7 and as an acceptable modality in treating traumatic wounds.8 Veterinarians at the University of Florida have reported its successful use in other applications including skin avulsions, degloving injuries, abdominal and thoracic wounds, surgical dehiscence, chronic nonhealing wounds, to prevent postoperative edema, and myofascial compartment syndrome.9 NPWT is contraindicated in a few cases in which cancer cells or overexposed vessels are present in the wound bed, in the face of active bleeding, or in devitalized tissue beds.
Complications are few and are usually technical issues related to the application or use of the system. Mild skin irritation of surrounding skin can develop from the tissue adhesive and drape. In my experience, as with any wound care tool, NPWT works best in carefully selected wounds. It has proven significantly effective in our patients in many traumatic wounds resulting in more comfortable and earlier wound closure. Let us help you to determine if NPWT may be helpful in your complicated wound cases.
Thanks to Jennifer Weh, DVM, DACVS-SA, from BluePearl in Washington for writing this article for Companion.
Meet Dr. Hannah Fore
After receiving her DVM from the University of Illinois, Dr. Fore completed a one-year, rotating internship with BluePearl Veterinary Partners at their hospitals in suburban Chicago. Get to know Dr. Fore…
“Throughout school, emergency clinicians Dr. McMichael and Dr. O’Brien inspired my passion for emergency medicine, and they encouraged me to pursue it as a career. Doing what I love every day makes me happy, and that’s what practicing emergency medicine does! After school, I pursued a small animal rotating internship. During that year I discovered that emergency medicine was what I wanted to practice for the rest of my life. I get to meet a variety of clients every day and see a wide variety of cases, some of my favorites being wound management. Just recently a small dog presented who had been attacked by a coyote. I was able to clean his wounds, stabilize and surgically place multiple drains. We were able to release him later that week, and he’s doing great!”
What aspects of emergency do you like the most?
I really enjoy working with the primary care veterinarian and providing exceptional after-hours care for their clients by keeping their patients stable through the weekend and facilitating a smooth transfer back to their clinic as needed.
What keeps you interested in cases day after day?
I enjoy the overall variety of cases that I get to see each day in addition to not having a set case schedule when I walk in the door. There is something very exciting about not knowing what the day will hold.