Trouble relaxing between beats is a growing cause of heart failure.
Your heart spends at least half the day relaxing. This isn't vacation time, mind you, but a vital and surprisingly complex part of the pumping cycle. If you're lucky, after each contraction your heart muscle relaxes effortlessly, springing open to fill with blood. If it doesn't, you could have — or be headed toward — a "new" condition known as diastolic heart failure.
Heart failure means that the heart isn't circulating blood efficiently enough to meet the body's demands. Until recently, the term referred mostly to weak, flabby heart muscle that couldn't squeeze hard enough to move sufficient blood around the body (systolic heart failure). Yet up to half of people with symptoms of heart failure have thick, muscular hearts that pump just fine. Their problem is heart muscle that doesn't relax properly between beats. This is called diastolic heart failure.
Although it is sometimes billed as a new condition, diastolic heart failure has been around as long as systolic heart failure. We're just more aware of it now, thanks to the growing use of diagnostic tools such as the echocardiogram. Up to half of the 550,000 Americans who develop heart failure each year have the diastolic variety.
Why the heart can't relax
Open space inside the ventricles can be restricted by heart muscle that "bulks up" due to overwork or other causes or that stiffens and loses it flexibility.
A single heartbeat actually has two separate phases. During systole (SIS-tuh-lee), the heart's large lower chambers, the ventricles, contract. This forces blood out of the heart and through the arteries. During diastole (die-ASS-tuh-lee), the ventricles relax and fill with blood in preparation for the next contraction.
Relaxation isn't a passive event. It's an active process that requires energy, raw materials, and coordination. And it's vital to adequate circulation. If heart muscle can't fully relax between beats, then the ventricles can't fully open. This curbs the amount of blood they can collect for the next heartbeat, which means each contraction pumps less blood than it should.
Such inefficient pumping sends less oxygen and nutrients to the body. Some people handle this without experiencing any symptoms. In others, the higher pressures behind the ventricles cause fluid to back up in the lungs and legs.
Too thick or too stiff
The heart's ventricles can have trouble filling with blood for two main reasons. Overworked heart muscle can "bulk up," like a weightlifter; this reduces the open space inside the ventricles. Alternatively, the heart muscle may stiffen and become less flexible.
Bulking and stiffening are sometimes the result of genetic signals. Most of the time, though, they have more immediate causes. High blood pressure is one of the most common causes of diastolic trouble. Diabetes, cholesterol-clogged arteries, and narrowed heart valves also contribute to the problem. Less common causes include conditions that cause protein, iron, and other substances to infiltrate heart muscle. Such conditions include amyloidosis, hemochromatosis, and sarcoidosis.
From the outside, diastolic problems look much like systolic problems. Like water behind a dam, blood backs up in the lungs and the rest of the body. This can lead to
- shortness of breath with mild activity, such as easy walking
- difficulty breathing, especially when lying down
- swollen legs and feet.
A simple test called an echocardiogram can tell the difference between systolic and diastolic disease. Using sound waves to make moving pictures of the beating heart, it can detect thickening of the heart muscle, limited space inside the ventricles, narrowing of one or more heart valves, and other telltale signs or causes of diastolic trouble.
Treating diastolic problems
Diastolic heart failure is a relatively new entity, so how best to treat it is an open question. There aren't yet drugs that reliably help the heart relax more quickly or more completely. And few large clinical trials of new and old drugs included people with diastolic trouble.
Treatment for diastolic heart failure focuses on relieving symptoms and halting or even reversing the underlying causes. It usually takes a multi-pronged approach.
Fluid control. The more fluid in your body and bloodstream, the harder your heart must work. Limiting the amount of salt (sodium) in your diet and watching how much you drink can ease breathing, reduce swelling, and lighten your heart's workload.
Pressure control. The long-term damage wrought by high blood pressure can lead to diastolic heart failure or make it worse. That's why controlling blood pressure is one of the best things you can do to avoid or control this condition.
Rhythm control. Contraction and relaxation are most effective when the heart's chambers work as a team. Atrial fibrillation (rapid and uncoordinated beats in the upper chambers) worsens diastolic trouble. Controlling it is important.
Exercise. The breathlessness and fatigue brought on by activity often prompt people with diastolic heart failure to become less and less active. That may keep symptoms at bay, but it actually makes the problem worse. A tailored exercise program can strengthen your heart, slow your heart rate, and improve the condition of muscles in your heart and throughout your body.
Drug therapy. A cornucopia of medications can help ease symptoms and take aim at the underlying causes of diastolic disease. These include
- diuretics (water pills) to get rid of excess fluid
- beta blockers to slow the heart rate. Fewer beats per minute means more time for the ventricles to fill with blood between beats
- calcium-channel blockers and long-acting nitrates to relax blood vessels, especially those that feed the heart muscle
- ACE inhibitors or angiotensin-receptor blockers to reduce blood pressure and reverse some of the physical changes that lead to thickening of the heart muscle.
(This article was first printed in the November 2004 issue of the Harvard Heart Letter. For more information or to order, please go to www.health.harvard.edu/heart.)
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