Introduction

With more veterinary cardiologists, radiologists and internal medicine specialists working in small animal practice and the increasing availability of traveling sonographers, many veterinary technicians may find themselves assisting with a cardiac ultrasound or echocardiogram on a dog or cat with confirmed heart disease or a newly diagnosed heart murmur. While chest radiographs can reveal the overall size of the heart from the outside, an echocardiogram (echo) uses sound waves to generate a real time two-dimensional image inside the atria, ventricles, and great vessels to aid in diagnosis and treatment. The room used to perform echoes should be a quiet zone, especially when handling a nervous dog or cat. Ultrasound supplies, adjustable lighting, the echo machine and a functional table to lay the patient on are needed. In addition, effective restraint and positioning of the animal by support staff is necessary to obtain diagnostic images in a timely manner. This will sometimes require the administration of intravenous (IV) or intramuscular (IM) sedatives to an overly anxious or aggressive patient. Some will be asymptomatic with mild heart disease, while others could be hemodynamically unstable or in heart failure. Sedation should be administered cautiously, using low doses of agents with the least adverse effects on cardiac and respiratory function. At NCSU, a low dose of the tranquilizer Acepromazine is used and often combined with the opiatesBuprenorphine or Butorphanol. Before proceeding with sedation, or if it is not an option, there are some distraction techniques that can be tried to avoid it. The goal is to have a stable animal cooperative enough to place a transducer on the thorax for ten to fifteen minutes of imaging.

Echo Supplies

Make sure the echo sonographer has everything needed within reach. This will include a set of clippers, a spray bottle of alcohol to part the hair-coat over the chest and plenty of ultrasound gel. Alcohol breaks down skin oils present in the dog and cat and allows for good contact of the gel. Gel is placed on the active end of the echo probe or transducer to enhance image quality by eliminating air that causes the sound waves to refract or scatter. In addition, a tap cart on wheels stocked with supplies should be nearby in case large volume pericardial, pleural or peritoneal effusion is discovered and needs to be removed.

Echo Room Lighting

A dimly lit room is optimal for viewing the black, white, and grays of echo video clips and stills. A combination of fluorescent overhead lights which can be turned off and recessed lighting in the ceiling that can be dimmed during the study seems to work best. A small lamp placed on a counter in the room and turned away from the echo screen will also provide dim lighting.

Echo Table Design

The echo table should be constructed of sturdy material such as fiberglass to support a heavy patient. A soft, non-slip pad placed on top can provide comfort for an older or frail patient. A hydraulic lift to raise and lower the table via a foot pedal allows for easier lifting and dismounting of large dogs. It also ensures a comfortable standing position for staff holding the patient during the study. A cut out section should be present in the middle of the echo table or at either end. This allows the operator to hold the transducer underneath the patient to obtain images from the down side lateral thorax. The table should be designed to slant downwards at a slight angle towards the echo sonographer to allow the heart to fall toward the transducer.

Echo Machine

The echo machine used for canine and feline studies should employ phased array transducers with varying degrees of penetration to create a fan shaped beam for adequate two dimensional images of the heart. The ability to perform motion-modes, color flow, and spectral Doppler studies is paramount to an accurate diagnosis by the veterinarian. Care and maintenance of ultrasound equipment is important. A cleaning with a mild soap solution should be compatible with most systems. Keep air filters, track balls, and control panels free of animal hair, dander and ultrasound gel. If air intake filters become clogged with hair, the machine can over heat and may shut down unexpectedly. The transducers must be handled carefully and never dropped as they contain piezoelectric crystals which send out and receive sound waves to generate images. Archiving patient studies onto storage media may also be the responsibility of veterinary staff. Use an ultrasound company with good customer support.

Restraining the Dog or Cat for an Echo

Most studies begin with the patient held in right lateral recumbence by one or two staff members to obtain the right parasternal long axis and short axis views of the heart. Placing the patient on its side allows the heart to lay closer to the chest wall and compresses the lungs to decrease air artifact. The person restraining the front end of the patient pulls the right down leg forward to facilitate placement of the transducer onto the chest wall at the level of the heart. The top leg is allowed to hang loosely down. If only one person is available to hold a large dog, an elongated sand bag or “sand snake” can be placed over the back end. Shaking or panting in dogs results in excessive chest motion interfering with image quality and can be minimized by either laying a hand gently but firmly on the “up” chest wall or by closing the mouth for a few seconds during image acquisition. Giant breed dogs may have to stand for echoes as the table may not be large or strong enough to support their weight. The staff member standing by the patient will have to pull the right or left foreleg forward and away from the chest for the echo sonographer to image the heart. Most echo views should be obtained with the patient attached to a corresponding electrocardiogram (ECG) tracing at the bottom or top of the screen to correlate stills and clips with either systole or diastole. Observation and treatment of a tachy or bradyarrhythmia at the beginning of the echo may need to be documented with a separate diagnostic ECG machine before switching to left apical views in left lateral recumbence.

Patient Demeanor and the Severity of Heart Disease

An echocardiogram is a non-invasive procedure and generally well-tolerated. Some patients that are challenging to work with in an exam room with their owners may be cooperative when taken for imaging. That said, the fear or anxiety experienced by some companion animals separated from their owners can result in shivering, shaking, excessive panting, or aggressive behavior such as biting, striking, or growling. Tachycardia caused by increased sympathetic tone in heart failure patients can become worse with stress. Older patients may be painful due to arthritis. Puppies and kittens can become frightened and struggle. Other patients may have trouble breathing due to congestive heart failure and be in need of chest radiographs or a brief initial standing echo until stabilized with oxygen, diuretics and anxiolytic medications. Complications obtaining echo views can occur and may include exacerbation of cardiac arrhythmias or formation of pulmonary edema. Some patients will respond to distraction while others may need to be muzzled or sedated. If intravenous sedation is to be administered, using a hind leg vein such as the medial saphenous in the cat and the lateral saphenous in the dog is recommended.

Distraction Techniques

Tactics used with uncooperative patients to avoid sedation for an echo include offering small amounts of food such as baby food, peanut butter, or dog and cat treats; having a third person by the head petting and talking to the animal; or having the owner present in the echo room during the exam.

Echo Sedatives Used at NCSU

1.  Acepromazine is an effective tranquilizer that does not provide analgesia. Low doses are recommended for animals with cardiac disease because of its adrenaline blocking effects on vascular smooth muscle resulting in vasodilatation. Lowering arterial blood pressure normally does not affect a patient with adequate systolic function; however, if cardiac output is already poor due to conditions such as dilated cardiomyopathy or pericardial effusion, acepromazine can cause hypotension and collapse. Acepromazine may also lower the seizure threshold in some canine breeds. At NCSU, it is used alone or combined with Buprenorphine or Butorphanol. The pharmacy dispenses it in a dilute form of 1 milligram (mg) per milliliter (ml), allowing small doses to be given accurately.

2.  Buprenorphine is a partial opiate agonist that blocks pain at the mu receptor in the central nervous system and is used primarily as an injectable long lasting analgesic in the dog and cat. It is compatible with acepromazine and can also be applied to the buccal mucosa. It is considered safe to give to patients with cardiac disease and is used frequently at NCSU. It comes in 1 ml vials at the strength of 0.3 mg/ml.

3.  Butorphanol is a partial opiate kappa agonist and antagonist at the mu receptor and is used as an analgesic for treating mild to moderate pain. It is compatible with acepromazine and comes in 1 mg and 2 mg per ml vials and at 10mg per ml in a 10 ml bottle.

4.  Ketamine inhibits NMDA or memory receptors in the CNS and is considered a dissociative anesthetic agent. It increases sympathetic tone, so effects on the cardiovascular system may include tachycardia and hypertension at higher doses. Ketamine is not recommended in cats with hypertrophic cardiomyopathy. At NCSU, ketamine is used in low doses on fractious cats that are not adequately sedated after receiving acepromazine combined with an opiate. Ketamine comes in 10 ml vials at 100 mg/ml. Many cats experience pain when injected IM; administering the agent slowly with a small gauge needle may alleviate this. Eyes will remain open after administration, so don’t forget to lubricate them.

Commonly Used Echo Sedation Protocols at NCSU

Dog

 Acepromazine 0.01–0.03 mg/kg used alone or mixed with Buprenorphine 0.0075 mg/kg IV or IM

 Acepromazine 0.01–0.03 mg/kg mixed with Butorphanol 0.1–0.2 mg/kg IV or IM

Cat

 Acepromazine 0.01–0.02 mg/kg used alone or mixed with Buprenorphine 0.01 mg/kg IV or IM

 Acepromazine 0.01–0.02 mg/kg mixed with Butorphanol 0.2 mg/kg IV or IM

Contraindicated Sedative

Dexmedetomidine is an alpha2 agonist that depresses sympathetic tone, reducing contractility of the heart muscle and causing vasoconstriction of peripheral arteries resulting in bradycardia and transient hypertension. It will adversely affect systolic function measurements taken by echo and should not be used for this imaging procedure. Even more importantly, its negative inotropic effects make it an unwise choice for sedating dogs and cats with heart disease.

The Fractious Feline

Fractious cats can be especially challenging to restrain for an echo. The best advice is to stay clear of the “danger zone” of front claws and face. Work slowly and quietly from the side and handle with thick towels placed over the shoulder blades. One strategy used to pull the front down leg forward for an echo, is to loop a long strip of tape around it with a large tab at the end. This keeps the restrainer’s right hand far away from the front end. Face muzzles may be difficult to place on an unsedated cat. If sedation is needed; a protocol employed at NCSU is to administer Acepromazine 0.02 mg/kg mixed with Butorphanol at 0.2 mg/kg IM. If more sedative is needed, Ketamine is administered at 5–10 mg IV or IM.

Conclusion

In North Carolina, the number of boarded veterinary cardiologists has increased from four in 1998 to eight in 2012. Cardiology Residents in training at the NCSU Veterinary Health Complex have grown from one to three DVMs. While this increase may not be typical for all areas of the country, it could be predictive of a future trend. As the number of these specialists rise, there is going to be more need for knowledgeable and trained staff to help them perform echocardiograms on dogs and cats.

References

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