Harvard Heart Letter

Uncovering a hidden cause of stroke

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To measure and monitor a wrist pulse:
1. Place two ngers on the inside of the
wrist at the base of the thumb.
2. Press lightly with the pads of your
ngers until you nd a pulse.
3. Hold for about 20 to 30 seconds to
check if the pulse is irregular.
4. Keep your ngers in place for another
60 seconds and count the beats.

Longer monitoring for irregular heart rhythms could be useful for people in danger of a brain attack.

During a bout of atrial fibrillation (afib), the rhythmic contractions in the heart muscle's upper chambers (the atria) are replaced with an ineffectual quiver. Although the irregular heartbeat is not usually life-threatening, the rhythm abnormality can have dangerous repercussions. Blood that pools in the atria when the heart does not pump forcefully can stagnate and form clots, which may then travel to the brain and cause the type of stroke known as an ischemic stroke.

More than one in six ischemic strokes can be traced to atrial fibrillation. However, an even larger percentage of ischemic strokes—between 20% and 40% of the total number—occur without any explanation at all, says Dr. Moussa Mansour, director of the Atrial Fibrillation Program at Harvard-affiliated Massachusetts General Hospital. These mysterious events are known as cryptogenic strokes, and there is growing suspicion that unrecognized afib may be to blame for some of them.

Intermittent episodes

With atrial fibrillation, periods of irregular heartbeats are likely to come and go, lasting from a few seconds to several days. In some people, an episode is marked by distressing symptoms such as palpitations, dizziness, or chest pressure. But for many others, the rhythm disturbances pass silently.

Currently, people hospitalized after an unexplained stroke undergo 24 hours of electrocardiogram (ECG) monitoring as well as a battery of brain and artery imaging tests. If no heart rhythm irregularities are apparent, people often leave the hospital with instructions to take an antiplatelet medicine such as aspirin. They generally are not given more powerful blood thinners, the drugs of choice for stroke prevention when you have afib. But if monitoring continues for a long enough time, a surprising proportion of these people do eventually show evidence of afib, says Dr. Mansour.

Armed with knowledge

The understanding that second strokes could be averted in many cases has fueled research into the most effective techniques for uncovering hidden heartbeat irregularities. The possibilities range from easily learned measures to high-tech implanted electronics. "The general idea is that if you do more cardiac monitoring, you can catch more afib than if you do nothing," says Dr. Mansour. "There are several ways to do this, from using external monitors or an implantable recorder to carefully checking the pulse."

At the high-tech end of the spectrum is an insertable cardiac monitor. This small device is implanted just under the skin of the upper chest to record ECG data on a continual basis. More traditional electronic monitoring methods include external devices, such as the 24-hour continuous Holter monitor and the 30-day loop memory recorder. Both these devices run on portable battery packs worn on the waist and track ECG activity via electrodes attached to the chest.

Finally, a recent study in Neurology showed that an action as simple as carefully monitoring your pulse can be a valuable tool. People who had strokes and their family members were specially trained to feel for fluctuations in heart rate and rhythm. Their ability to detect an irregular heartbeat was surprisingly accurate when compared with ECG results and readings taken by health care professionals.

Personalized care options

Which technique is best? "The decision depends on how great your suspicion is that afib is present as well as the particular needs and preferences of the patient," says Dr. Mansour. For example, an elderly person with limited access to transportation may fare better by having a family member or caregiver perform pulse monitoring three times a day for the six months following a stroke. On the other hand, a person in his or her 50s who intends to stay active for many years may be a good candidate for more aggressive monitoring. Timing is also a factor, says Dr. Mansour. Taking pulse measurements or using an external monitor for a month may uncover the problem in a person with a strong likelihood of having afib. In less clear-cut cases, an insertable cardiac monitor can keep tabs on rhythm changes for a year or more. "They are all good options that we can use to individualize care and are better than what we had before," says Dr. Mansour.