September 09, 2012

ECG Diagnosis of Cardiac Conditions

Electrocardiograms (ECGs) are performed with the major goal to obtain information about the electrical function of the heart. Medical uses for this information, however, are varied and often need to be combined with knowledge of the structure of the heart and physical examination signs to be interpreted.

This article is for Medical Students & Professionals
This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find the ECG article more useful, or one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.
In this article:
ECG diagnosis
MCQ exam: clinical scenario
MCQ exam: answer
MCQ exam: explanation

ECG diagnosis

The electrocardiogram (ECG) is the most important test for interpretation of the cardiac rhythm, conduction system abnormalities, and the detection of myocardial ischemia. The ECG is also of great value in the evaluation of other types of cardiac abnormalities including valvular heart disease, cardiomyopathy, pericarditis, and hypertensive disease. Finally, the ECG can be used to monitor drug treatment (specifically antiarrhythmic therapy) and to detect metabolic disturbances.

A systematic approach to interpretation of the ECG is imperative in order to avoid overlooking any abnormalities. Pattern recognition is helpful, but it is important to review all aspects of the ECG to not miss something.

MCQ exam: clinical scenario

What is the most likely diagnosis:

a) pulmonary embolism
b) early repolarization
c) acute pericarditis
d) acute myocardial infarction
e) Myocarditis

MCQ questions & answers on

MCQ exam: answer

The correct answer is C.

MCQ exam: explanation

The electrocardiogram (ECG) is a useful, simple tool that may aid in the diagnosis of acute pericarditis. Typical ECG findings include diffuse concave-upward ST-segment elevation and, occasionally, PR-segment depression. ECG changes of both acute myocardial infarction and early repolarization can appear similar to ECG changes of acute pericarditis. However, these conditions can usually be excluded by an accurate history, physical examination and recognition of a few key features on the ECG.

In this ECG of a patient with acute pericarditis, note diffuse concave-upward ST-segment elevation, ST-segment depression in aVR, and PR-segment depression which is best demonstrated in leads II and V3. Note lack of reciprocal ST-segment changes, an important feature differentiating acute pericarditis from acute myocardial infarction. Also note that the ST/T ratio is greater than 0.25, a finding frequently indicative of acute pericarditis.

Also see this separate Q&A article, ECG diagnosis of medical conditions.

1). UpToDate: ECG tutorial: Basic principles of ECG analysis. Available online:

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