Interpreting EKGs

What is an EKG and why it matters

An electrocardiogram, also called an EKG or ECG, records voltage changes produced by the heart as it beats. The output is a waveform on paper or a digital screen. Clinicians read that waveform to learn whether the heart is beating regularly, whether electrical signals travel normally through the chambers, and whether there are clues to reduced blood flow, prior injury, or enlargement of heart muscle.

For preventive cardiology and primary care, an EKG is a low cost, rapid test that helps triage symptoms such as chest discomfort, palpitations, dizziness, or unexplained shortness of breath. It also provides baseline information for patients with hypertension, diabetes, or a family history of heart disease. At The NY Center for the Prevention of Heart Disease we combine EKG findings with clinical risk assessment and other tests when needed.

Key concepts every reader should know

How we use the tracing

When we interpret an EKG we look for three broad groups of findings.

• Rhythm: is the heart regular, and is the rhythm sinus or an arrhythmia such as atrial fibrillation.
• Conduction and intervals: PR interval, QRS width, and QT interval help detect blocks or abnormal conduction.
• Ischemia and structural clues: ST segment and T wave changes, axis shifts, and voltage may suggest ischemia, prior infarction, or chamber enlargement.

Basic waveform components

• P wave indicates atrial electrical activity.
• PR interval shows conduction from atria to ventricles.
• QRS complex marks ventricular depolarization.
• ST segment and T wave represent ventricular repolarization.

Common abnormalities and what they mean

Below are abnormalities we encounter frequently, with why they matter.

• Atrial fibrillation, seen as an irregularly irregular rhythm without distinct P waves, raises stroke risk and often prompts anticoagulation decisions and rhythm management, topics we cover in our Atrial Fibrillation Treatment information.
• ST segment depression or elevation can indicate active ischemia or infarction and usually triggers urgent evaluation or imaging.
• Prolonged QT interval increases risk of dangerous ventricular arrhythmias and influences medication choices.
• Left ventricular hypertrophy produces high QRS voltages and repolarization changes, often related to long standing hypertension, which we manage through our Hypertension Management service.

When an EKG is not enough

An EKG gives electrical information but has limits. It cannot directly image coronary arteries or measure ejection fraction. When we need structure or perfusion details we use other tests, chosen for the clinical question.

1. Ambulatory monitoring. For intermittent palpitations or syncope we may use a Holter monitor or longer event recorder.
2. Stress testing. To assess exertional chest pain or ischemia risk, exercise or pharmacologic stress testing adds functional information.
3. Cardiac imaging. Echocardiography or advanced imaging such as coronary CT angiogram provide structural and anatomic detail not visible on an EKG. See our topic on Coronary CT Angiogram and Cardiac Imaging Explained for more.

Comparison of common cardiac tests

How we interpret EKGs at our center

At The NY Center for the Prevention of Heart Disease we place EKG interpretation in the context of risk assessment and patient history. With more than 30 years of clinical experience, Dr. Bradley Radwaner and our team evaluate the tracing, compare it to prior studies, and decide whether ambulatory monitoring, laboratory testing, or imaging is the next step.

We coordinate findings with primary care and other specialists when needed, particularly for patients with diabetes, hypertension, or a family history of heart disease. Our approach is evidence based and focused on prevention, not just diagnosis. To learn about our overall approach see our Preventive Cardiology page and our Cardiologist overview.

Related services and topics

Interpreting EKGs connects to many of our services and topics. Relevant pages include our clinical services and procedural overviews.

• Cholesterol Management, for lipid risk that influences ischemic risk.
• Atrial Fibrillation Treatment, since EKGs detect AFib and guide anticoagulation discussions.
• Advanced Cardiac Testing, when EKG plus exam suggest further evaluation.
• Heart Specialist consultations for complex or unclear findings.

Common questions patients ask

Will an EKG detect every heart problem?

No. An EKG detects many electrical abnormalities but cannot see coronary artery blockages directly or all structural problems. It is often the first step, followed by imaging or ambulatory monitoring when needed.

How should I prepare for an EKG?

No special preparation is usually required. Wear a loose shirt that is easy to remove, and avoid lotions on the chest. Tell your clinician about medications and symptoms you have experienced.

What if my EKG is abnormal?

An abnormal tracing prompts review of symptoms and history, comparison with prior EKGs, and targeted follow up. That may include ambulatory monitoring, blood tests, echocardiography, or stress testing depending on the suspected issue.

Helpful resources and next steps

For deeper reading and related topics we link to internal pages that explain risk factors and testing in detail. Helpful topics include:

• Heart Disease Risk Factors
• Cardiac Biomarkers
• Choosing A Cardiologist