Congenital Heart Disorders
Although most feline heart disorders are diagnosed in middle-aged and elderly cats, some kittens are born with them. Fortunately, these congenital cardiac conditions are relatively rare, occurring in only one or two percent of kittens. According to Marc Kraus, DVM, a senior lecturer in the department of clinical sciences at Cornell University’s College of Veterinary Medicine, the most commonly diagnosed among these disorders are: ventricular septal defect (VSD), patent ductus arteriosus (PDA), and mitral valve dysplasia (MVD).
Understanding the nature of these conditions requires a basic awareness of the feline heart’s structure and function. About the size of a small apricot, it is a hollow, muscular organ located in the center of the chest. Its main functions are (1) to rid circulating blood of waste products (mainly carbon dioxide); and (2) to provide the body with a steady supply of refreshed, oxygen-rich circulating blood. Both the left and right sides of the organ have an upper chamber (atrium), which collects blood, and a lower chamber (ventricle), which pumps blood. First, the right atrium collects oxygen-depleted blood from the body, and when the chamber is full, propels it into the right ventricle. From there, it is pumped, via the pulmonary artery, into the lungs, where the carbon dioxide is removed and its oxygen supply is replenished. The blood then moves from the lungs to the left atrium and subsequently to the left ventricle, from which it is pumped—via the aorta—into the body’s circulatory system. In a healthy cat, the four heart chambers are separated internally by membranes (septa) and by one-way valves that keep blood moving in the proper direction. The most frequently diagnosed congenital disorders, notes Dr. Kraus, involve problems associated either with the heart’s valve structure and operation or with holes in the septa.
Most common of all is ventricular septal defect (VSD), which is a hole in the ventricular septum, the normally sturdy barrier of tissue that separates the ventricles and prevents blood from being diverted (shunted) from one of these lower chambers to the other. “Two major factors determine the consequence of this condition,” says Dr. Kraus. “One is the size of the hole, and the other is the difference in the pressure of the blood within the two ventricles.” A small VSD, he points out, will be of no significance, and an affected kitten can be expected to thrive and live a normal life. However, he says: “A moderate-sized hole may cause enough shunting of blood to produce clinical signs, such as open-mouth breathing and exercise intolerance. And if the hole is large enough, the cat can go into congestive heart failure.”
The second most common congenital cardiac condition is patent ductus arteriosus (PDA). Prior to birth, a blood vessel called the ductus connects a fetus’s aorta to its pulmonary artery, which leads to the lungs. In a normal kitten, this artery closes within a day or two after birth. But in PDA the artery remains open (patent), resulting in excessive passage of blood from the animal’s heart to its lungs. Although the condition can potentially lead to heart failure, says Dr. Kraus, it can be surgically corrected within a few months after a kitten is born—or even earlier if the surgeon thinks the kitten is big enough and healthy enough. “The surgery simply involves going in and tying the artery off,” he notes.
Yet another frequently diagnosed congenital cardiac disorder in cats is mitral valve dysplasia (MVD). In this condition, which is most often genetically inherited, the mitral valve, located deep within the heart, exhibits diminished functionality and is unable to efficiently perform its important function, which is to regulate the flow of blood from the left atrium to the left ventricle. As a result, backed-up blood accumulates in the left atrium. Exercise intolerance, weight loss, vomiting, and the potential for blood clot development are among the consequences of this condition.
These three disorders, as well as pulmonary stenosis, aortic stenosis, and a variety of other congenital feline cardiac disorders, tend to share a salient clinical sign. That is, a veterinarian will notice during the course of a routine examination the presence of a heart murmur—a rhythmic “swooshing” sound instead of a mild, steady, soft beat. Although some affected kittens may respond favorably to medicinal or, in some cases, surgical treatment, the prognosis for a severe congenital defect is generally poor. Minor defects, however, may be well tolerated and even allow a normal lifespan.