When the pyrexic patient has a new heart murmur

You are presented with a sick, pyrexic dog. During your examination, you hear a heart murmur that wasn’t documented at the last visit.

A nurse picks up a murmur on a poorly hospitalised patient that they didn’t hear on yesterday’s checks.

Is it a new finding? Is it simply a flow murmur associated with fever, or could something more sinister be happening?

Infective endocarditis might not be the first thing that springs to mind when treating a sick patient, but it’s an important differential to keep on the radar. This potentially life-threatening infection can damage the heart valves, cause acute cardiac complications and send infected material travelling around the circulation.

So, when should we suspect it, what should we look for, and why does recognising it early matter?

If you’d like more advice on your case after reading this article, you can use our telemedicine service, or 

Refer a case

What exactly is infective endocarditis?

Infective endocarditis (IE) is an infection of the inner lining of the heart, most commonly affecting the valves. In dogs, the aortic and mitral valves are most frequently involved.

Bacteria circulating in the bloodstream can attach to the valve surface and form infected vegetations, made up of bacteria, inflammatory material, platelets and fibrin. As these vegetations develop, they can damage the valve leaflets and prevent them from closing properly, resulting in valvular regurgitation.

Although underlying valve abnormalities can increase susceptibility, endocarditis can also develop on previously normal valves. It’s uncommon, but missing it can have serious consequences.

When should we suspect it?

The classic combination is a systemically unwell patient with a new or changing heart murmur. However, the presentation isn’t always textbook.

Things that should raise suspicion include:

• Persistent or recurrent fever, particularly when the source is unclear or the patient isn’t responding as expected.
• A new or changing murmur, especially in a patient with suspected bacteraemia or sepsis.
• Unexplained lameness, joint pain or shifting-leg lameness, potentially associated with embolic or immune-mediated complications.
• Unexpected arrhythmias, collapse or signs of poor perfusion.
• Evidence of thromboembolic disease or otherwise unexplained organ dysfunction.

A new murmur in a pyrexic patient doesn’t automatically mean endocarditis. Fever, anaemia and increased cardiac output can all produce flow murmurs. Equally, however, finding a plausible alternative explanation shouldn’t lead us to dismiss the possibility of underlying valvular infection when the wider clinical picture doesn’t fit.

And remember: although a murmur is common in dogs with IE, its absence doesn’t reliably exclude the disease.

Why is it so dangerous for the heart?

The problem isn’t simply that bacteria have reached the valve. It’s what happens when that valve starts to fail.

Acute valvular regurgitation

Destruction of the mitral or aortic valve can cause significant regurgitation, sometimes developing rapidly enough that the heart has little time to adapt. Severe mitral regurgitation can precipitate pulmonary oedema, while severe aortic regurgitation can compromise forward cardiac output and cause haemodynamic instability.

Congestive heart failure

Once valvular damage becomes haemodynamically significant, the patient may develop congestive heart failure. New tachypnoea, increased respiratory effort or unexpected deterioration in a septic patient should prompt reassessment for a cardiac complication rather than automatically being attributed to the primary illness.

Thromboembolism

Fragments of infected vegetations can break away and travel through the circulation, causing septic emboli. These can result in infarction and infection in distant organs, contributing to signs such as lameness, renal abnormalities or other unexplained organ dysfunction.

Arrhythmias and conduction disturbances

Infection involving the aortic root or surrounding tissues can extend beyond the valve itself, potentially causing abscess formation and damage to the cardiac conduction system. New arrhythmias, particularly when accompanied by other concerning cardiac findings, warrant further investigation.

What should we do next?

The key is to investigate the cardiac findings alongside the suspected infection.

• Echocardiography: This is the principal imaging investigation when IE is suspected. It can identify valvular vegetations, assess valve damage and regurgitation, evaluate chamber size and function, and look for complications. A negative initial scan doesn’t necessarily exclude IE if clinical suspicion remains high. Repeat reassessment during the hospitalisation treatment is useful to monitor.
• Blood cultures: Where feasible, obtain appropriate blood cultures before starting antibiotics, provided this doesn’t delay urgent treatment in an unstable patient. Culture results can help identify the causative organism and guide antimicrobial treatment.
• Electrocardiography (ECG): Useful if an arrhythmia is suspected or detected, particularly if the patient has collapse, pulse deficits or an unexpectedly irregular rhythm.
• Assess for cardiac consequences: Consider whether there is evidence of congestive heart failure, significant regurgitation, impaired perfusion or thromboembolic complications. Thoracic radiographs and other investigations should be guided by the patient’s stability and clinical signs.

If IE is suspected, early discussion with a cardiologist is worthwhile. The combination of echocardiographic findings, microbiology and the overall clinical picture is important, as no single finding reliably confirms or excludes every case.

The take-home message

Infective endocarditis may be uncommon, but in a systemically unwell dog, a new or changing murmur deserves attention.

Not every murmur in a pyrexic patient means there is a valve infection, and not every patient with IE has an obvious murmur. The important thing is to recognise when the cardiac findings don’t fit comfortably with the rest of the case.

When suspected sepsis and new cardiac abnormalities appear together, keep infective endocarditis on the differential list. Early recognition of valvular damage and its complications may make a real difference to how quickly the patient receives the investigations and specialist input they need.

Refer a case to us