Health Tips

Electrocardiography: A simple, safe way to monitor the heart

Electrical impulses are critical to the proper functioning of the heart, a muscle that is often compared to an efficient engine, complete with valves and a pumping system. At the core of the heart's electrical system is the sinus node, which acts as a generator or pacemaker. The sinus node governs the heart's four chambers as they contract and relax to form a rhythmic (sinus) heartbeat. In addition, certain cells act as electrical conduits that carry electrical activity to the working muscle. Given the proper electrical stimulus, the heart pumps blood at a consistent and appropriate pressure, volume, and rhythm.

However, if the electrical signals within the heart change in rate, regularity, or electrical conduction sequence, symptoms may result and occasionally irreversible damage may occur. Such changes may result from heart disease or may themselves affect heart muscle mass or can cause the heart's muscles to stretch, which can alter blood pressure and flow.

Fortunately, there is a painless, quick, non-invasive test–an electrocardiogram (EKG)–that allows cardiologists to accurately gauge the heart's electrical function by sensing internal electrical signals that arise from the heart and reach the body's surface.

"An EKG can reveal characteristics–duration, shape, and sequence–of electrical signals from a single heartbeat or from a series of beats," says James A. Reiffel, MD, Professor of Clinical Medicine and a leading cardiologist at Columbia University Medical Center. "The EKG can reflect conditions that impair blood flow to the heart or cause the heart to be overloaded in volume or in pressure, as well as revealing other irregularities."

These conditions may reflect any of a number of diseases, including valve disorders, diabetes, high blood pressure, coronary artery disease, inherited disorders, or cardiomyopathies - heart disease of sometimes unknown origin. "Changes in electrical signals may be specific to a particular disorder, but often a change is common to several kinds of heart disease," Dr. Reiffel says. "Therefore, once an abnormality is detected by EKG, we use other diagnostic tests to elucidate the specific underlying problem." Because it is rapid, risk-free, and inexpensive, electrocardiography can be used serially to follow the progression of the disorder.

For example, electrocardiography is an excellent screening tool for high blood pressure (HBP, also called hypertension), which, if not adequately controlled, can cause the heart muscle to thicken, placing undue stress on the heart. HBP has been associated with heart rhythm disturbances and a shortened lifespan. Thickening of the heart can be assessed very accurately with echocardiography, but this technology is expensive. Instead, electrocardiography, a far less expensive technology, can be used to take indirect measures of thickening.

EKG Measurements On the Go

In an electrocardiogram, electrosensors are placed on the chest and hooked to a machine that takes measurements. Once the sensors are in place, it takes less than a minute to record the measurements. The entire exam takes about five minutes, and results are available immediately.

Usually, EKGs are done in a doctor's office with the patient lying prone on an examining table. However, some patients have symptoms such as fainting (syncope) or dizziness that may be related to a heart irregularity that may not occur during the EKG with the patient at rest. In these cases, the physician may order a stress test, which measures the heart's electrical function during an increasingly strenuous exercise cycle. In other cases, an EKG may be coupled with imaging technology that reveals changes in the size or thickness of the heart, evidence of underlying disease.

"If a rhythm is too slow, not enough blood will be pumped to the brain. If it is too fast, the heart's ability to fill between beats is impaired, and again, not enough blood gets to the brain," Dr. Reiffel says. For patients with intermittent events, an ambulatory EKG allows physicians to measure the patient's electrical heart signals when symptoms are occurring. Called a Holter recording, for the physician who invented it, this device essentially brings the EKG to the patient. In a Holter recording, the EKG leads are attached to a portable device that records every heartbeat over a 24-hour period. In addition, the patient is asked to record activities and symptoms over this period in a diary, enabling the physician to correlate data from the Holter recording with the patient's activities. "A Holter recording allows physicians to see transient rhythm disturbances that may have prognostic importance," Dr. Reiffel says.

For patients whose symptoms occur less frequently–once a week or even once a month–memory loop recorderscan be worn for weeks at a time if necessary. The devices are similar to the Holter recorder, but they are smaller and can sample heartbeats continuously, storing data only when the patient pushes an activation button. When activated, the device captures the event itself, as well as the 30 to 60 second period before and after the event. Thus, if a patient wearing this device experiences dizzinsess or palpitations, he or she would push a button, alerting the device to save information from the previous 30 to 60 seconds through the symptomatic period.

There also are similar recording devices that are literally the size of a credit card and can be carried for months at a time in a jacket pocket or pocketbook, Dr. Reiffel says. They are activated by being held against the skin so that the back of the device, which contains the electrodes, can record the cardiogram. Moreover, in a nod to Dick Tracy, companies are now manufacturing similar monitors that fit inside a wristwatch: by simply touching two buttons on either side of the watch, the patient activates the device to record the cardiogram. Such devices can store data for up to two months. The newer memory loop recorders even auto-trigger for an atrial fibrillation, one of the most common disorders, and one that may produce no symptoms, and thus no reason for a patient to self-activate.

Life-Saving Monitoring of Chronic Disorders

Ambulatory EKG monitoring can save lives in people with the following disorders:

• Atrial fibrillation and other persistent arrhythmias

  Atrial fibrillation, the most common, sustained, symptomatic arrhythmia encountered in healthcare, is particularly common in the elderly, patients with hypertension, diabetics, those who have recently had cardiac surgery, and those with pulmonary dysfunction. Ambulatory EKG is useful in documenting the effectiveness of medications in controlling fibrillation or reducing the amount of time spent in fibrillation. Medications then can be adjusted according to EKG data.

• Fibrillation plus certain risk markers for development of blood clots
  

  Some, although not all, patients who suffer from fibrillation are at risk for developing blood clots, which can place them in danger of stroke or blindness. Again, the risk is greater for older patients, those with high blood pressure, diabetics, and those suffering from heart failure or certain valve conditions. These patients are often given blood thinners to reduce clot risk. "We also may be more proactive in using medications to reduce periods of fibrillation for these patients, depending on EKG data," Dr. Reiffel says.

• Screening for possible arrhythmia
  

  Using EKGs to screen for fibrillation and other serious rhythm disorders is useful for patients with a history of arrhythmia, those who have an asymptomatic arrhythmia that is detected by an in-office EKG, or those with diseases or familial disorders that are commonly associated with arrhythmias. The EKG can indicate if the patient needs a blood thinner or if heart rates are unstable.

Thus, the EKG can be used to ascertain the presence of abnormalities that reflect heart disease, and it also can be used to assess alterations in disease that may occur over time, either progressively or regressively.

When to Have an EKG

When to schedule an EKG depends on such factors as overall health, age, and medical history. A healthy young individual may be tested every few years, while someone undergoing anti-arrthymic drug therapy may be tested every few days. Someone having heart surgery may be tested frequently over a period of one to two months for atrial fibrillation, a condition that often occurs postoperatively.

EKG testing is advised for people with certain congenital, or inherited, familial heart disorders that are associated with serious consequences, including sudden death. An EKG may give clues to these serious disorders, even though the individual appears to be healthy. Such phenomena include:

• Long Q-T syndrome, which is often the cause of death in young athletes who die suddenly
• Hypertrophy—a thickening of heart muscles for unexplained causes
• Pre-excitation—an electrical alteration

"The problem is that healthy young people usually don't get EKGs," Dr. Reiffel says. "These conditions are relatively rare and it simply is not cost-effective to arrange EKG testing for every high school athlete. However, EKG can be used for public health screening if there is reason to suspect underlying heart disease. If a family member has suffered a known arrhythmia or sudden death, screening may be warranted to detect evidence that the disorder has been inherited."

A Look to the Future

In looking ahead to the development of new EKG technology, Dr. Reiffel foresees a device that does not produce a paper record. "This machine would measure heartbeat intervals. If the heart is normal, it would indicate 'normal.' If it detects an irregularity, it would produce an on-screen message such as 'screen further.' To my knowledge, nobody has done this yet, but the technology to do this exists. It is a matter of how we want to apply health care resources, but we certainly can do it."

Another advance that is becoming a reality is use of the Internet to view EKGs over long distances. "Already we are starting to see systems that record the EKG signal and transmit it wirelessly to the web for review at remote sites or monitoring stations," Dr. Reiffel says.

For more information about electrocardiography, or to schedule an EKG, please call 1.800.227.2762.