August 02, 2010

Q&A: ECG Diagnosis of Medical Conditions

The overall goal of performing an ECG is 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

Numerous diagnoses and findings can be made based upon electrocardiography. Overall, the diagnoses are made based on the patterns. For example, an "irregularly irregular" QRS complex without P waves is the hallmark of atrial fibrillation; however, other findings can be present as well, such as a bundle branch block that alters the shape of the QRS complexes. ECGs can be interpreted in isolation but should be applied – like all diagnostic tests – in the context of the patient. For example, an observation of peaked T waves is not sufficient to diagnose hyperkalemia; such a diagnosis should be verified by measuring the blood potassium level. Conversely, a discovery of hyperkalemia should be followed by an ECG for manifestations such as peaked T waves, widened QRS complexes, and loss of P waves.

MCQ exam: clinical scenario

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 B.
This is early repolarization.

MCQ exam: explanation

One must be able to distinguish acute pericarditis from normal early repolarization. This pattern is most common in teenage boys and men in their 20s. These individuals differ from pericarditis patients in that the clinical syndrome of pain and dyspnea is absent, PR-segment depression is present in some patients but uncommon, and, most important, the ECG does not, over time, evolve a pattern of return of the ST segment to baseline followed by T-wave inversion.

ECG comparing acute pericarditis, early repolarization and acute MI

Image above shows single electrocardiographic complexes comparing (left) acute pericarditis, (center) early repolarization and (right) injury pattern of acute myocardial infarction. Note the degree of ST-segment elevation is greater in the pericarditis complex than in the early repolarization complex. Important findings of acute infarction include the presence of Q waves and a more convex upward ST segment, both of which are present in the right complex.

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

1). Mark A. Marinella. Electrocardiographic Manifestations and Differential Diagnosis of Acute Pericarditis. Am Fam Physician. 1998 Feb 15;57(4):699-704

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