Cardiovascular System Diseases

14.1 Heart Disease

As birds live longer and diagnostic techniques improve, cardiac disease is being diagnosed more frequently.²⁰ Heart disease in birds with enlarged, poorly functioning hearts can be difficult to detect and may mimic other problems, such as respiratory, hepatic, or ovarian disease. Cardiac disease has been associated with atherosclerosis in pet birds, and potential risk factors are a sedentary lifestyle, a high-fat diet, and too much cholesterol in the blood. ³⁷

Clinical signs are weakness, depression or lethargy, increased respiratory rate and effort, and tachycardia (rapid heartbeat.) With right-sided heart disease, hepatomegaly (enlarged liver) and ascites (fluid in the body cavity) are common. In birds, right-sided cardiac disease is more prevalent than left-sided. Disease also may be subclinical, then flare up suddenly, with the bird going into cardiac arrest when diagnostic tests or treatments are attempted. Diagnosis is based on echocardiogram, and treatment includes the same cardiac drugs used in mammals. ²⁰
 

In this image of the bird, “on the lateral view of her body, you can see a white spike, kind of knife-shaped. That is a calcified aorta, arteriosclerosis. We can also see a small mass in her neck. These are geriatric issues. The fracture brought her in, and the heart and mass were incidental findings that will complicate her surgery (amputation) and recovery. There is also a mass in her left axilla (image courtesy Bart Huber; used with permission).³¹

Consultation with a cardiologist on any avian patient with suspected cardiac disease is advised. Diagnosis of the cardiovascular abnormality and the formation of a therapeutic plan require knowledge of avian anatomy and physiology as well as a veterinary cardiologist's diagnostic skills and medication recommendations. Radiographs and cardiac ultrasound can aid in the diagnosis.³⁷

"The stress of handling can increase intracardiac blood flow velocity 300% in avian patients; therefore, inhalant anesthesia or sedation is preferred over manual restraint when echocardiograms are performed in all but the most docile birds." ³⁷

Although most avian therapeutic regimens are still taken from those used in mammals, there are reports that indicate that cardiac drug therapy can improve cardiac function, thereby increasing the quality and length of the bird’s life ^37,43

14.2 Pulmonary Hypertension

The cardiovascular system of birds differs anatomically and physiologically from that of mammals. Mammals are able to maintain sufficient pulmonary vascular resistance, but birds are not. "This results in the inability of the pulmonary vasculature to accommodate increased cardiac output by either altering vessel diameter or changing the number of vascular channels being used. This causes the high incidence of pulmonary hypertension syndrome in poultry and right-sided heart disease in psittacine birds. For geriatric psittacine patients with pulmonary hypertension, vasodilator therapy should be explored. Macaw asthma may cause pulmonary hypertension from chronic capillary hypoxia” (too little oxygen).³⁷Some chronically obese birds will display infiltration of fat into the myocardium (the muscular tissue of the heart), and this can be seen at necropsy. The bird will then suddenly succumb to the disease with no other findings on histopathologic examination. ⁴³
 

14.3 Atherosclerosis

Atherosclerosis is a chronic inflammatory and degenerative disease of the arterial wall. The blood vessels are narrowed due to progressive accumulation of inflammatory cells, fat, cholesterol, calcium, and cellular debris which form fibrous and fatty plaques within the blood vessel. It may lead to stenosis (narrowing of the blood vessels), ischemia (poor blood supply to the heart or brain), thrombosis (blood clot in a blood vessel), hemorrhage, and aneurism (bulge in a blood vessel). Amazons and African greys have the highest numbers reported, followed by cockatiels, lovebirds, Eclectus parrots, cockatoos, and macaws.  ³⁷

Atherosclerosis is caused by high-fat, high-cholesterol diets, lack of exercise, age, species susceptibility, and exposure to some infectious agents. The result is long-term, chronic inflammation. The type of dietary fat consumed affects the development of atherosclerosis more than the total amount of fat consumed. ³⁷ Diets high in Omega 3 and 6 fatty acids and herbs protect against atherosclerosis in geriatric parrots.” ⁴⁷

Atherosclerosis leads to stroke, heart attack, and vascular disease and is seen in parrots with increasing frequency. The clinical signs for birds include circulatory conditions, lethargy, dyspnea, fainting, sudden falling, nervous symptoms due to blood loss in areas of the body, and sudden death.
 

Atherosclerosis refers to damage from lesions in the arteries. It is being seen more often in geriatric psittacine birds; however, African grey parrots may develop this at a younger age. "Atherosclerotic plaques in the coronary vessels cause abnormal vascular flow and loss of integrity of the heart’s lining. These changes in vessel walls can initiate thrombosis. In birds, lesions are primarily in the aorta and brachiocephalic arteries (a blood vessel that originates from the aortic arch).³⁷ One study showed that 86% of the Amazon parrots with atherosclerosis who were in aviary and zoo populations were over eight years old, and many were over 15 years old. In one report, the incidence of atherosclerosis in the study group was 91.9% in African greys and 91.4% in Amazons.^37,43
 

Risk factors include:

• Increased age (most affected birds are 10–15 years old or older)
• Reproductive disease (predominantly female) due to the effects of estrogen on lipid, protein, and calcium metabolism in reproductively active female birds
• Hepatic disease
• Concurrent myocardial fibrosis (abnormal thickening of the heart valves)
• High-calorie, high fat diets
• Hypercholesterolemia (high levels of cholesterol in the blood)
• Lack of exercise, sedentary lifestyle.¹⁸

Clinical signs include:

• Diminished blood flow through the arteries
• Severe lesions in the heart
• Other cardiac disease
• Congestive heart failure
• Sudden death¹⁸

Patients are often presented for:

• Falling or collapsing and exercise intolerance
• Transient or persistent weakness and lethargy
• Dysfunction of one or more limbs
• Altered and reduced mentation, such as disorientation or confusion
• Blindness or anisocoria (unequal size of the pupils)
• Seizures, tremors, or convulsions
• Vestibular proprioceptive signs (perception of body position and movement)
• Paresis of one or both pelvic limbs
• Extension and rigidity of one leg and wing
• Clenching of the toes
• Ataxia and difficulty perching
• Regurgitation
• Dyspnea (difficulty breathing)
• Ascites (fluid build-up in the abdomen)¹⁸

Although it can occur at any time, one sign that is often observed in the practitioner’s office is syncope (a temporary loss of consciousness caused by a drop in the blood pressure) during exertion.³⁷ Often the client reports sudden symptoms which resolve a short time later. These signs are consistent with stroke, but rarely is this confirmed diagnostically. It can be difficult to distinguish between atherosclerosis and stroke.¹⁸

14.4 Diagnosis and Treatment

Diagnosis can be challenging. "Radiographically, the right aortic arch may be enlarged and show increased density. Lipemia (fat in the blood) is often present, and marked increases in cholesterol and triglyceride concentrations may be seen. Unfortunately, definitive antemortem tests are lacking." ¹⁸

Medical treatment is anecdotal. A variety of treatments have been advocated to lower cholesterol levels, but none appears to be consistent in its efficacy. Essential fatty acids (flax seed oil and VetOmega") have been advocated and used to reduce cholesterol and inflammation. Weight loss, increased activity, and dietary improvement will improve the overall health and hopefully prevent atherosclerotic plaques. In some cases, clinicians may choose to begin therapy with lipid-lowering medications such as statins. Some studies have shown that ginseng is effective is lowering the plasma cholesterol levels in birds. Atherosclerosis, degenerative heart disease, and congestive heart failure should be considered in any geriatric patient with the above signs.³⁷
 

At necropsy, grossly thickened arterial walls are seen, as are cholesterol layers within the aorta and large arteries. Microhemorrhage, metaplasia, fibrosis, and mineralization are also found. "These lesions cause increased arterial resistance that affects the heart. Right-heart failure can lead to congestion, atrophy, and eventually cirrhosis of the liver. Sudden death is commonly seen in birds who appear to be in good condition and even overweight. Birds experience decreased blood supply to the brain as a result of severe narrowing of the carotid arteries. He may lose awareness of his surroundings in the days or weeks before his death." ⁵⁸