An enlarged, misshapen heart can be a striking finding during a cattle necropsy. It also can be an easy place to stop looking.
Dr. Brad White, professor at Kansas State University, wants veterinarians to resist that temptation.
“If you only look at the heart, we don’t have the whole picture,” says White.
That message is supported by a series of recent studies from Kansas State University researchers examining cardiac morphology, heart scores, concurrent disease and histopathologic changes in beef cattle. The research suggests that while heart size and shape can provide important clues, the heart needs to be interpreted alongside the liver, lungs and other organs.
An Abnormal Heart Isn’t Necessarily CHF
Congestive heart failure (CHF) is an increasingly recognized cause of mortality in feedyard cattle, but diagnosing it can be difficult. Clinical signs overlap with other common diseases, particularly respiratory disease, and postmortem diagnosis also can be challenging.
One recent study evaluated 346 feedyard deaths and found cardiac enlargement or a misshapen ventricle (CEMV) in 106 cattle, or 30.6%. Only 11 animals met the study’s definition of CHF, which required cardiac enlargement or ventricular remodeling along with chronic passive congestion of the liver and at least two additional signs of congestion, such as pleural, pericardial or peritoneal effusion.
Cardiac remodeling was considerably more common than confirmed CHF.
The researchers also found that heart measurements could objectively distinguish some of the morphological changes. CEMV cattle had wider hearts, thinner left ventricular walls and larger right ventricular lumen areas than cattle without CEMV.
Yet those measurements did not tell the whole CHF story.
White notes that digital heart measurements were associated with heart score but “weren’t always associated with CHF.”
That is an important distinction for interpreting heart scores. A score can document cardiac remodeling without necessarily establishing that the animal had clinical heart failure.
Heart Scores Need Context
Heart scoring remains a useful way to describe gross cardiac morphology. In the Kansas State study, scores of 3, 4 and 5 were associated with a greater probability of CEMV than scores of 1 or 2.
However, even a high score does not automatically equal CHF.
Nine of the 11 CHF cases in the study had heart scores of 3–5, but two CHF cases had scores of 2. Meanwhile, many cattle with scores of 3–5 did not meet the study’s CHF definition.
White says the tendency to interpret heart score as a progression from normal to disease can be misleading.
“[It] makes us want to think in a progression,” he says. “What they actually saw on the performance side was that both cattle with very high scores and cattle with a score of 1 had some performance differences.”
The broader point is that a heart score describes what the heart looks like. It doesn’t necessarily explain why it looks that way.
The Liver May Help Complete the Picture
If the heart is one piece of the diagnostic puzzle, the liver may be another particularly important one.
In work examining cardiac and hepatic histopathology in 87 feedyard mortalities, moderate to severe cardiac necrosis and fibrosis was found across the range of gross heart scores. Those cardiac changes were not significantly associated with CHF. Liver fibrosis was the only variable significantly associated with CHF probability.
Cattle with moderate to severe liver fibrosis had a model-adjusted 57% probability of being classified as CHF, compared with 4% for cattle with minimal liver fibrosis.
White points toward the same question from a different direction. Researchers are exploring whether liver evaluation could eventually help identify cardiac dysfunction in live cattle.
“The liver seems to be a pretty important indicator of what’s going on,” he says.
The work is still exploratory, but the concept is straightforward: rather than asking only whether the heart looks abnormal, veterinarians can look for evidence that cardiovascular dysfunction is affecting other organs.
Don’t Overlook the Lungs
The same principle applies to the lungs.
In a different study, researchers examined cattle at harvest and evaluated whether the lungs deflated normally after death. About 40% of the lungs failed to deflate, and cattle with lungs that failed to deflate were more likely to have abnormal heart scores.
The finding raises an important question about the relationship between pulmonary disease and cardiac remodeling.
White cautions against assuming that an abnormal heart necessarily represents a purely cardiogenic process.
“Before we blame this on purely a cardiogenic process, we need to evaluate what else is going on with that animal,” he says.
That is particularly relevant because respiratory disease and CHF can produce overlapping clinical signs, while pulmonary disease itself may contribute to the physiologic changes associated with cardiac remodeling.
Multiple Lesions May Be Part of the Diagnosis
The need to look beyond a single organ is reinforced by a separate study of 889 feedyard mortalities. Researchers found that 72% of cattle had more than one gross lesion, with an average of 2.3 lesions per animal. Pulmonary and gastrointestinal systems were the most frequently affected, while cardiovascular, gastrointestinal and pulmonary lesions occurred together in 6% of cases; cardiovascular and pulmonary lesions occurred together in another 5%.
This work emphasizes that necropsies should not necessarily end once a significant lesion is found. Their protocol assigned multiple causes when two or more lesions could have contributed to the animal’s death.
That concept is illustrated by one of White’s cases.
The calf had a congested liver and effusion, but its heart was not dramatically abnormal. At the same time, the lungs had significant bronchopneumonia. White describes it as a case that could qualify for both CHF and bronchopneumonia rather than forcing it into a single diagnosis.
“It doesn’t have to be a singular diagnosis,” White says.
That may be one of the most useful lessons from the research.
Look at the Whole Animal
When investigating suspected bovine heart disease, White supports a more comprehensive approach. An abnormal heart score should prompt additional evaluation rather than automatically becoming the final diagnosis.
White’s recommendation is straightforward:
“I don’t think the heart score tells us the whole picture. I think we need to look at the heart score, liver and lungs.”
That approach can provide a better understanding of whether cardiac remodeling represents CHF, another process affecting the heart, or one component of a more complicated disease picture.
The research also raises questions that remain unanswered. Some cattle show cardiac remodeling without the ancillary lesions associated with end-stage CHF, while others can have evidence of CHF without the most dramatic cardiac morphology.
For now, White’s message is a useful reminder at the necropsy table: don’t let the most obvious organ become the only organ you investigate.
