Exercise Test Forecasts Heart Patients’ Outcome

'Stress echo' results aid timing of mitral valve repair
Pulse trace on the screen

Cleveland Clinic cardiologists have found that a relatively simple treadmill stress test provides valuable insight about long-term medical outcomes in heart patients with a leaky mitral valve. 

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Patients with a leaky mitral valve and mitral regurgitation – a common defect where a backwash of blood surges between the heart’s left filling and pumping chambers – are usually diagnosed when their doctor hears a heart murmur. But they may not have other noticeable physical symptoms until the heart damage caused by the leaky valve becomes severe.

Surgical timing is controversial

There has been disagreement and controversy – and not much guidance from previous medical research – about when to operate to repair or replace a bad mitral valve. Should surgery be immediate, as many doctors presume, even though patients say they don’t feel bad? Or is it OK to wait, and if so, how long? What impact would a delay have on a patient’s long-term outcome? And are there indicators that might show when it’s advisable to operate?

Cardiologist Milind Desai, MD, and colleagues believed that a diagnostic tool called exercise echocardiography could answer some of those questions. The success rate for mitral valve surgery is very high and complications are few, but every operation entails some risk.

“The mortality and morbidity rates, while very close to zero, are never zero,” Dr. Desai said. “The question is, are there patients you could wait on and delay surgery, and are there others that need it now? And could exercise echocardiography help sort out those and aid in the decision-making?”

‘Stress echo’ measures endurance

Exercise echocardiography, commonly called “stress echo,” is a test where patients walk on a gradually steeper and faster-moving treadmill while their heart rate and blood pressure are monitored. Afterward, a probe touched to the chest bounces high-pitched sound waves off the heart to produce an image of the muscle at work, showing its size, movement and blood flow.

The point of the stress echo is to see how well the patient performs during vigorous activity. It provides information on many fronts:

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  • Physical endurance.
  • How quickly heart rate drops toward normal following exercise.
  • How blood pressure responds to exercise.
  • The presence of abnormal heart rhythms.
  • Whether there is adequate blood supply to the heart at peak activity.
  • The pressure level within the heart.

By comparing a patient’s test results to those of healthy people of the same age and gender, a cardiologist can identify valve-related problems, such as a struggling and enlarged heart, even in patients who haven’t noticed a physical decline.    

Study confirms stress echo’s predictive role

Dr. Desai and his colleagues studied 884 Cleveland Clinic patients with moderate to severe mitral valve disease and no obvious symptoms who underwent stress echo testing between 2000 and 2011. The researchers tracked how those patients fared over time, before and after they were operated on to fix their leaky mitral valve.

What they found, according to a study published in the medical journal Circulation, is that stress echo results can indeed help identify patients that will do worse during follow-up.  

Mitral regurgitation patients in the study who didn’t perform as well as expected for their age and gender on the treadmill test – whose heart rates took longer to return to normal, and whose endurance levels were not as high as they should be, even though they weren’t reporting symptoms – tended to fare poorly long-term. Patients with abnormal heart fluttering (known as atrial fibrillation), reduced pumping ability, or increased pressure within the heart, also tended not to do well. They had an increased risk of death, strokes, heart attacks and hospital admissions for congestive heart failure.

On the other hand, leaky-valve patients whose exercise capacity on the stress echo test was as at least as good as their healthy counterparts did very well, in terms of their medical outcomes, in the long run.

Exercise tolerance is key indicator

So the study confirmed the predictive value of the stress echo test for patients with bad mitral valves. If patients aren’t feeling symptoms but aren’t able to tolerate the expected amount of exercise on the treadmill test – and particularly if they have heart fluttering, reduced pumping ability or other clinical warning signs – then immediate mitral valve surgery probably is warranted, rather than waiting until symptoms appear.

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Conversely, “if you hit 100 percent or more of your exercise capacity on the treadmill test, your long-term outcomes are good,” Dr. Desai said. “One could make an argument that we could potentially hold off on surgery for a while.”

How long the surgery can be delayed in patients who pass the stress echo test is the subject of ongoing research by Dr. Desai’s group.

Whether this test’s predictive ability extends to other cardiac conditions remains to be conclusively proven. “So I would not venture to say that it’s useful in the general population,” Dr. Desai said. “Everybody in the general population does not need to come in for a stress echo.”

But Cleveland Clinic’s new research demonstrates that the test can help reduce the guesswork in determining when to make mitral regurgitation repairs.

“This could be an objective way of deciding which patients should proceed, and more importantly, which patients should not proceed, with surgery,” Dr. Desai said. For both physicians and patients, “you’re more confident and comfortable.”

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