en españolElectrocardiograma (ECG)
An electrocardiogram (ECG or EKG) measures the heart's electrical activity. This can help doctors tell how the heart is working and identify any problems.
The ECG can help show the rate and regularity of heartbeats, the size and position of the heart's chambers, and whether there is any damage.
How Is an ECG Done?
There is nothing painful about getting an ECG. The patient is asked to lie down, and small metal tabs (called electrodes) are fixed to the skin with sticky papers. These electrodes are placed in a standard pattern on the shoulders, the chest, the wrists, and the ankles.
After the electrodes are in place, the person is asked to hold still and, perhaps, to hold his or her breath briefly while the heartbeats are recorded for a short period. The patient also might be asked to get up and exercise for a while.
The information is interpreted by a machine and drawn as a graph. The graph shows multiple waves, which reflect the activity of the heart. The height, length, and frequency of the waves are read in the following way:
- The number of waves per minute on the graph is the heart rate.
- The distances between these waves is the heart rhythm.
- The shapes of the waves show how well the heart's electrical impulses are working, the size of the heart, and how well the individual parts of the heart are working together.
- The consistency of the waves provides fairly specific information about any heart damage.
What Can an ECG Diagnose?
A person's heartbeat should be consistent and even. ECGs look for abnormally slow and fast heart rates, abnormal rhythm patterns, conduction blocks (short-circuits of the heart's electrical impulses that cause rhythm inconsistencies between the upper and lower chambers) — and four types of heart damage:
- ventricular hypertrophy — an abnormal thickening of the heart muscle
- ischemia — caused by an abnormally decreased blood supply
- cardiomyopathies — abnormalities in the heart muscle itself
- electrolyte and drug disturbances — these can change the heart's electrochemical environment
Computerized ECGs can be used with other tests to get a multimedia account of the heart. These other tests include echocardiograms (which are basically "ultrasound" tests that bounce sound off the heart and use the echoes to make an image) and thallium scans (which are kind of like X-rays and use a radioactive tracer, injected into the bloodstream, to help draw a picture of the heart).
In the past, the ECG was recorded on a machine that drew on long strips of paper, with records from each electrode presented in a standard sequence. Now the ECG tracings are stored as computer files that can be called up and printed.
When Are Results Ready?
Results of the ECG are available immediately. In fact, the ECG machine's computer even provides an instant interpretation of the findings as it makes the report. However, the doctor also might ask an expert, usually a cardiologist, to help analyze and interpret the ECG. Some of the ECG results may be subtle, requiring an expert eye to detect them.
The study, conducted among 400 healthy children, identified previously undiagnosed cardiac conditions in 5.8% of the kids, according to Victoria L. Vetter, MD, and colleagues from the University of Pennsylvania.
All of the children studied were evaluated with a physical examination, an ECG, and a cardiac echo.
In 2.5% of the children screened, most around age 12 and white, the heart conditions uncovered were potentially serious -- yet none of the children had a positive family history, the researchers reported online in the American Heart Journal.
"We were surprised to find ten children with these serious cardiac abnormalities," Vetter told MedPage Today.
"But what you have to realize is that in a small screening study the percentages can be high, and when you add to the numbers the percentage will come down. We've done thousands of these evaluations now and the percentage of children with these conditions is closer to 1%," she explained in a phone interview.
In the U.S., cardiac screening is only recommended for competitive athletes, with detailed personal and family histories as well as physical examinations, but ECGs are reserved for those with positive histories.
Other countries, such as Italy and Israel mandate ECG screening of young athletes.
Lack of efficacy and costs have been cited as barriers to screening before sports participation in the U.S.
However, studies have consistently shown that ECG screening can detect three to four times more abnormalities than the history and physical alone, the researchers noted.
Whether or not screening of the wider pediatric student population would be feasible, and how common these conditions really are also have been unanswered questions.
"We really don't know how many young people are dying from these conditions. It's thought to be somewhere between 100 and 1,000 each year in the U.S., but that's just an estimate," Vetter said.
To explore the feasibility of large-scale screening, she and her colleagues undertook a pilot study at the Children's Hospital of Philadelphia in children without known heart conditions.
Detailed personal and family histories were obtained for all, along with physical examinations, 15-lead ECG, and echocardiography, during a 30- to 60-minute visit.
The children's mean age was 11.8 years, slightly more than half were boys, and almost 90% were white.
Among the potentially serious abnormalities uncovered during screening included prolonged QT interval, Wolff-Parkinson-White syndrome, complex ventricular ectopy, ostium primum atrial septal defect, and left ventricular dysfunction.
Many benign normal variants also were seen on ECG, such as sinus arrhythmia and nonspecific ST-T wave changes.
Slightly more than 4% had left ventricular hypertrophy, but in most cases the measurements were only slightly above the upper limit of normal according to the Davignon normative values.
However, they noted, if more rigorous criteria were used for interpretation, only 2.3% would have been considered as having left ventricular hypertrophy. This observation emphasizes the need for updated, more specific normative standards, according to the authors.
Just under 3% had elevated or borderline QTc intervals; most of these were false positives that were normal on repeat testing.
Echocardiography identified five serious abnormalities such as dilation of the aorta. Of these five, three were seen only on the echocardiogram.
An additional 5% of children in the program were found to have hypertension, and all children with abnormalities were referred for appropriate treatment.
Concerns that have been raised about screening include the possibility of misclassification and unnecessarily preventing children from participating in physical activities, but in this study most false positives were quickly identified.
Limitations of the study included the small number of conditions identified and the possibility of selection bias.
Also, the study was not powered to determine the prevalence of cardiac abnormalities.
"We should do a large enough study, with 15,000 to 25,000 children, where we do the history and physical, as well as the ECG and echo. Let's find out the best way to identify these conditions, and the best way to treat them, and what the effects of that treatment are," Vetter said.
She also pointed out that many of these conditions are inherited, so identifying one family member with an abnormality means the rest of the family can be screened.
The study was supported by the Children's Hospital of Philadelphia.
The authors reported no financial conflicts.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
- Explain that screening healthy children with electrocardiography (ECG) and echocardiography could detect previously undiagnosed conditions that might lead to sudden cardiac arrest.
- Note that among the potentially serious abnormalities identified among the children studied included prolonged QT interval, Wolff-Parkinson-White syndrome, complex ventricular ectopy, ostium primum atrial septal defect, and left ventricular dysfunction.