Electrocardiograms (EKG/ECG): Reading Your Heart's Electrical Activity

An electrocardiogram—called an EKG or ECG—is one of the most common and useful tests for evaluating heart health. It's quick, painless, and provides a wealth of information about your heart's electrical system. Understanding what this test measures and its limitations can help you better appreciate its role in your cardiac care.

What Is an EKG?

Your heart is controlled by electrical signals that coordinate each heartbeat. These signals travel through your heart in a specific pattern, causing the chambers to contract in the right sequence to pump blood effectively.

An EKG records this electrical activity by detecting tiny electrical changes on your skin. Electrodes placed on your chest, arms, and legs pick up these signals and display them as waves on paper or a computer screen. These wave patterns reveal how your heart is functioning electrically.

What an EKG Can Detect

The patterns on an EKG can reveal various conditions and abnormalities:

Heart Rhythm Problems

An EKG clearly shows your heart rate (how fast your heart beats) and rhythm (whether it beats regularly or irregularly). It can identify:

• Atrial fibrillation and other arrhythmias
• Extra heartbeats (premature contractions)
• Abnormally fast heart rates (tachycardia)
• Abnormally slow heart rates (bradycardia)

Heart Attack

An EKG can show signs of a current heart attack or indicate that you've had one in the past. It can also help determine which area of the heart is affected and how severe the damage might be.

Inadequate Blood Flow

Changes in the EKG pattern can suggest that parts of your heart aren't receiving enough blood and oxygen, which may indicate coronary artery disease. However, the EKG must often be done during symptoms or during a stress test to capture these changes.

Structural Abnormalities

An EKG can provide clues about:

• Enlarged heart chambers
• Thickened heart muscle
• Congenital heart defects
• Inflammation of the heart (pericarditis or myocarditis)

Electrolyte Imbalances

Abnormal levels of potassium, calcium, or magnesium in your blood can affect your heart's electrical activity and show up on an EKG.

When EKGs Are Used

An EKG might be ordered in various situations:

• Symptoms evaluation: Chest pain, palpitations, shortness of breath, dizziness, or fainting
• Routine physical: Some doctors include EKGs in checkups, especially for people with risk factors
• Pre-surgical clearance: Before certain surgeries, particularly in older adults
• Monitoring: Checking how heart medications or other treatments are working
• Follow-up: After a heart attack or cardiac procedure
• Emergency situations: When heart attack or dangerous arrhythmias are suspected

How the Test Is Performed

An EKG is one of the simplest medical tests you'll encounter:

Preparation

No special preparation is needed. You can eat and drink normally and take your regular medications unless specifically instructed otherwise. You'll be asked to undress from the waist up, and men may need small areas of chest hair shaved for better electrode contact.

During the Test

You'll lie flat on an examination table. A technician will attach about 10 electrodes (small sticky patches) to your chest, arms, and legs. These connect via wires to the EKG machine.

You'll need to lie very still and breathe normally while the machine records your heart's electrical activity. The actual recording takes less than a minute, though the entire appointment including electrode placement and removal typically takes 5-10 minutes.

The test is completely painless. The electrodes simply detect electrical signals—they don't deliver any electricity to your body.

After the Test

The electrodes are removed, and you can immediately resume all normal activities. There are no side effects or recovery period.

Types of EKG Testing

Different situations call for different approaches to EKG monitoring:

Resting EKG

This is the standard test described above, capturing your heart's electrical activity while you're lying still. It provides a snapshot of your heart rhythm and function at that moment.

Exercise EKG (Stress Test)

This records your heart's electrical activity during physical exertion, typically while walking on a treadmill. It can reveal problems that only appear when your heart is working harder.

Holter Monitor

This portable device continuously records your heart's electrical activity for 24-48 hours while you go about your normal daily activities. It's useful for detecting intermittent arrhythmias that might not show up during a brief office visit.

Event Monitor

Similar to a Holter monitor but worn for weeks or months, an event monitor only records when you activate it (usually when you feel symptoms) or when it detects abnormal rhythms automatically.

Understanding EKG Results

An EKG generates a series of waves labeled P, Q, R, S, and T. Each represents a different phase of your heart's electrical cycle. The size, shape, duration, and timing of these waves tell your doctor how your heart is functioning.

Normal Results

A normal EKG shows regular rhythm, appropriate heart rate (usually 60-100 beats per minute at rest), and wave patterns within expected ranges. However, "normal" can vary somewhat between individuals based on age, body size, and other factors.

Abnormal Results

An abnormal EKG doesn't automatically mean you have serious heart disease. Many factors can cause EKG changes, some insignificant. Your doctor interprets results in the context of your symptoms, medical history, and other tests.

Some abnormal findings require immediate action, while others may just need monitoring. Your doctor will explain what your specific results mean and whether any follow-up is needed.

Important Limitations

While valuable, EKGs have important limitations to understand:

Snapshot in Time

A resting EKG captures only a few seconds of your heart's activity. If you have an intermittent problem that isn't occurring during those seconds, the EKG will appear normal. This is why longer monitoring or stress testing is sometimes needed.

Can't Detect Everything

A normal EKG doesn't guarantee you don't have heart disease. For example:

• You can have significant coronary artery blockages with a normal resting EKG
• Some valve problems don't show up on EKGs
• Early stages of some heart conditions may not yet cause EKG changes

Interpretation Requires Expertise

Reading an EKG is a skill that requires training and experience. Subtle findings might be missed without expertise, and normal variants can sometimes be misinterpreted as abnormal.

EKG Screening in Healthy People

Whether healthy people without symptoms should get routine EKG screening is debated. Major medical organizations generally don't recommend routine screening EKGs for low-risk individuals without symptoms because:

• Most people will have normal results that don't change their care
• False positive results can lead to unnecessary worry and testing
• Many important heart conditions aren't reliably detected by a single resting EKG

However, EKGs may be more useful for people with cardiac risk factors, family history of heart disease, or certain medical conditions. Discuss with your doctor whether screening EKGs make sense for your individual situation.

What to Do With Your Results

After your EKG, your doctor should explain the results and their implications. Don't hesitate to ask questions:

• What did the EKG show about my heart?
• Are any findings concerning?
• Do I need any follow-up tests?
• Should I make any changes based on these results?
• When should I have another EKG?

If your EKG is abnormal, remember that many abnormalities are minor or require only monitoring. Follow your doctor's recommendations for any additional testing or treatment.

EKGs in Emergency Situations

In emergency departments and ambulances, EKGs play a critical role in rapidly diagnosing heart attacks and dangerous arrhythmias. Time is crucial in these situations, and an EKG can be performed in minutes to guide immediate treatment decisions.

If you're experiencing chest pain, severe shortness of breath, or other concerning symptoms, an EKG will likely be one of the first tests performed. This quick test helps doctors determine whether you're having a cardiac emergency requiring immediate intervention.

The Bigger Picture

An EKG is a valuable tool in assessing cardiac health, but it's just one piece of the puzzle. Your doctor considers your EKG results alongside your symptoms, physical examination, blood tests, imaging studies, and other cardiac testing to understand your overall heart health.

The test's simplicity, safety, and speed make it a cornerstone of cardiac evaluation. While it has limitations, the information it provides is often crucial for diagnosing and managing heart conditions.