Mild to severe heart muscle impairment linked to higher stroke risk

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Although previous studies have linked heart failure to increased stroke risk, this is the first evidence that even mildly impaired heart function may be an independent risk factor for ischemic stroke. Ischemic strokes are caused by a blood clot that blocks blood flow to a part of the brain.

The finding raises the question of whether LVD should be included in the evaluation of a person's stroke risk. Mild, symptomless LVD is present in 3 percent to 6 percent of the general population, according to this study.

"Clinically overt heart failure has been associated with an increased risk of stroke," said Marco R. Di Tullio, M.D., senior author of the study and professor of clinical medicine at Columbia University in New York. "Mild and often asymptomatic LVD is not usually among the things we consider to predict stroke risk. These results suggest that maybe it should be."

In LVD, the heart fails to pump blood as effectively as a normal-functioning heart.

Associations between impaired heart function and stroke have come primarily from studies of patients who survived heart attacks. The association between LVD and stroke in the general population had not been as clearly evaluated in any large studies. Researchers compared rates of LVD in stroke patients and in controls enrolled in the Northern Manhattan Study (NOMAS).

The analysis focused on 558 NOMAS participants who underwent echocardiography, a test that uses soundwave technology to test heart functioning. The study group comprised 270 stroke patients with first time ischemic stroke (average age 70) and 288 stroke-free participants (average age 69) who were matched with the patients according to age, gender and ethnicity or race. Echocardiography was performed within three days from stroke onset in the stroke group.

Reflecting the multiethnic makeup of NOMAS, about 32 percent of the study group was black, 49 percent was Hispanic, and 17 percent was white. Stroke risk factors, such as high blood pressure, smoking and atrial fibrillation (rapid, irregular heartbeat), were more common in one or more ethnic groups of stroke patients compared to controls, and diabetes was more common in stroke patients across all ethnic/race groups.

Using echocardiography, researchers documented LVD in 24.1 percent of stroke patients and 4.9 percent of the control group.

Regardless of its severity, LVD was significantly more common in stroke patients than in controls. It was moderate-severe in 13.3 percent of stroke patients compared to 2.4 percent of controls; and it was mild in 10.7 percent of stroke patients versus 2.4 percent of the controls. After controlling for the influence of other stroke risk factors, LVD remained a statistically significant predictor of increased stroke risk.

LVD had a significant effect on stroke risk across the entire spectrum of patients. LVD of any degree increased the odds of stroke more than three-fold in men, almost five-fold in women, over three-fold in patients under age 70, and almost five-fold in patients 70 and older. The link was also detected in all ethnicities.

Di Tullio and his co-authors said results appear to "contradict the belief that stroke risk parallels the severity of LVD, and indicates that a significantly increased risk of stroke should be considered to be present even in the much larger fraction of patients with mildly decreased [LV function]."

The finding that even mild LVD increases stroke risk poses a problem because the condition often causes no clear symptoms and is diagnosed incidentally during an evaluation for some unrelated condition, Di Tullio said. The study also poses a treatment-related dilemma.

"What to do next [after diagnosing LVD] is not so clear because there is no evidence that treating these patients with the drugs we use to treat heart failure would change the risk of stroke," Di Tullio said.

The authors emphasized that further studies are required to assess whether drug treatment could lessen the chance of stroke associated with LVD. How LVD increases ischemic stroke risk is unclear.

The researchers are conducting a follow-up study involving stroke-free people who have been evaluated by echocardiography. By following them over time, Di Tullio and his associates hope to further clarify the association between LVD and stroke by defining the annual risk of stroke associated with LVD of different degrees.

American Heart Association