Learn What Your ECG Results Mean About Heart Health

Understanding the Basics of an ECG Test

An electrocardiogram, commonly called an ECG or EKG, is a medical test that records the electrical activity of your heart. Every time your heart beats, it creates tiny electrical signals. An ECG machine picks up these signals and displays them as lines on paper or a computer screen. The test takes about 5 to 10 minutes and is painless.

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During an ECG, a technician places 10 small stickers called electrodes on your chest, arms, and legs. These electrodes connect to wires that lead to the ECG machine. The machine reads the electrical signals traveling through your heart and prints out a graphic representation of these signals. The result is a series of waves and lines that show your heart's rhythm and electrical activity.

There are different types of ECG tests. A resting ECG is performed while you sit or lie down quietly. A stress ECG, also called a treadmill test, records your heart's electrical activity while you exercise on a treadmill or stationary bike. A Holter monitor is a portable device you wear for 24 to 48 hours that continuously records your heart's rhythm throughout your daily activities. Each type provides different information about your heart health.

Doctors order ECG tests for many reasons. They may want to investigate chest pain, shortness of breath, or heart palpitations. An ECG can also be part of a routine checkup for people with risk factors for heart disease, such as high blood pressure, high cholesterol, or a family history of heart problems. Some patients receive an ECG before major surgery to ensure their heart can handle the stress of an operation.

Practical takeaway: If your doctor orders an ECG, understand that it's a safe, non-invasive way to look at how your heart is working electrically. There's no special preparation needed for a resting ECG, though you should wear clothing that allows easy access to your chest.

Reading the Wave Patterns on Your ECG

An ECG printout displays several distinctive waves and segments, each with a specific meaning. Learning to recognize these patterns helps you understand what your results mean. The main features you'll see are labeled as P wave, QRS complex, T wave, and ST segment. These names may sound technical, but each one tells a story about what your heart is doing electrically.

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The P wave is the first small bump you see on the ECG line. It represents the electrical signal that causes your upper heart chambers, called the atria, to contract and pump blood into the lower chambers. A normal P wave is small and rounded, typically less than 0.12 seconds wide. If the P wave looks abnormal, it may suggest problems with the atria or that the electrical signal is traveling in an unusual path.

The QRS complex is the largest and most distinctive feature on an ECG. It shows the electrical activity that causes your lower heart chambers, called the ventricles, to contract powerfully and pump blood out to your body. The QRS complex normally lasts about 0.08 to 0.12 seconds. A wider QRS complex may indicate a delay in how the electrical signal travels through the ventricles, which could suggest a conduction problem or other heart issues.

The T wave comes after the QRS complex and represents the electrical recovery, or "repolarization," of the ventricles. A normal T wave is typically rounded and points upward in most leads of the ECG. An abnormal T wave—one that's inverted (pointing downward), too tall, or too flat—may suggest heart strain, damage, or inadequate blood flow to the heart muscle.

The ST segment is the flat line between the QRS complex and the T wave. In a normal ECG, this line should be at a baseline level. If the ST segment is elevated (higher than baseline) or depressed (lower than baseline), it can be a sign of serious conditions like a heart attack or ischemia (insufficient blood flow). The ST segment is particularly important because changes in this area often require urgent medical attention.

Practical takeaway: When you receive your ECG results, ask your doctor to point out these specific features and explain whether they appear normal or abnormal in your test. Understanding these basic patterns will help you follow your doctor's explanation of your results.

Common ECG Findings and What They May Indicate

Your ECG results may show a pattern described as "normal sinus rhythm," which is the healthiest finding. This means your heart is beating at a regular rate between 60 and 100 beats per minute, and all the electrical signals are traveling through your heart in the normal sequence. If your results show normal sinus rhythm, it's a good sign that your heart's electrical system is functioning as it should.

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Arrhythmias are irregular heartbeats, and they're among the most common ECG findings. Atrial fibrillation (AFib) is a condition where the upper chambers of the heart beat irregularly and rapidly. On an ECG, AFib appears as an irregular pattern without distinct P waves, and the baseline looks wavy or irregular. According to the American Heart Association, about 2.7 to 6.1 million Americans have AFib. This condition increases the risk of stroke and may require treatment with blood thinners or heart rate control medications.

Atrial flutter is similar to AFib but shows a more organized pattern on the ECG, often appearing as a sawtooth-like baseline. Premature atrial contractions (PACs) are extra heartbeats that originate in the atria. These often feel like your heart is skipping a beat and appear as early P waves on the ECG followed by a pause. Many people experience occasional PACs without serious consequences, though frequent PACs may warrant further investigation.

Ventricular arrhythmias originate in the lower chambers of the heart and are generally more concerning than atrial arrhythmias. Premature ventricular contractions (PVCs) are extra beats from the ventricles. They show up on the ECG as wide, abnormal-looking QRS complexes. While occasional PVCs can occur in healthy people and may cause no symptoms, frequent or sustained PVCs may indicate underlying heart disease. Ventricular tachycardia is a rapid series of ventricular contractions that requires urgent medical attention because it can be life-threatening.

Bradycardia means your heart rate is slower than 60 beats per minute. This can be normal in athletes, but in other people it may indicate a conduction problem or that the heart's natural pacemaker isn't working properly. Tachycardia means your heart rate is faster than 100 beats per minute at rest, which may suggest thyroid problems, infection, dehydration, or heart disease.

Practical takeaway: If your ECG shows an arrhythmia, don't panic. Many arrhythmias are benign and require no treatment, while others may need monitoring or medication. Your doctor will determine whether your specific finding requires follow-up testing or treatment based on your symptoms, medical history, and overall health.

Signs of Heart Damage and Ischemia on ECG

An ECG can reveal signs that your heart muscle has been damaged or that it's not receiving enough blood flow. These findings often appear as changes in the ST segment or T wave, or as abnormalities in the QRS complex. Recognizing these patterns is important because they may indicate conditions requiring treatment or lifestyle changes.

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Myocardial infarction, commonly called a heart attack, causes characteristic changes on an ECG. During an acute heart attack, the ST segment typically becomes elevated above the baseline. This finding is called ST elevation and requires emergency medical care. Even after a heart attack has occurred, the ECG may show permanent changes in the Q wave or T wave that indicate old scar tissue in the heart muscle. These changes can persist for months or years and help doctors identify that a person has had a previous heart attack.

Ischemia occurs when the heart muscle isn't receiving enough oxygen-rich blood, often due to narrowed coronary arteries. During ischemia, the ECG may show ST segment depression (the segment dips below the baseline) or T wave inversion. These changes may be temporary, appearing only during exercise or emotional stress, which is why stress testing is sometimes used to detect ischemia. Silent ischemia is a concerning condition where these ECG changes occur without the person experiencing any symptoms or chest pain.

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