Which EKG finding is most consistent with a pulmonary embolism?

Which EKG finding is most consistent with a pulmonary embolism?

• A. Increased QRS amplitude with tall R waves in limb leads and deep S waves in V1 and V2
• B. Notched P wave in leads I and II with an increased duration
• C. Sinus tachycardia with a right ventricular strain pattern, prominent S in lead I, Q wave and inverted T in lead III
• D. Prolonged QRS duration with QS complex in V1, monophasic R wave in leads I and V6

Answer: (C)

Pulmonary embolism often causes sudden right heart strain, and that stress shows up on the ECG as signs of an overworked right ventricle along with a fast heart rate. The most classic pattern you’ll see is sinus tachycardia with a right-ventricular strain pattern: a prominent S wave in the left lateral limb leads (reflecting a rightward shift of the QRS axis) together with a Q wave and T-wave inversion in the rightward lead III. This S1Q3T3 pattern is a recognizable clue that points toward acute PE in the right clinical context, even though it isn’t always present. Understanding why this pattern fits: the embolism raises pulmonary vascular resistance, loading the right ventricle and causing it to dilate and strain. The electrical axis shifts to the right, producing the deep S in lead I and the Q/T changes in lead III. Sinus tachycardia is the most common accompanying rhythm, driven by hypoxemia and sympathetic stimulation. Other findings described in the distractors align more with other cardiac conditions. Notched P waves with enlarged left atrium point to atrial enlargement from mitral disease. Patterns of QS or monophasic R waves across precordial and lateral leads can indicate myocardial infarction or conduction abnormalities, not the typical acute right-heart strain pattern seen with PE.

Pulmonary embolism often causes sudden right heart strain, and that stress shows up on the ECG as signs of an overworked right ventricle along with a fast heart rate. The most classic pattern you’ll see is sinus tachycardia with a right-ventricular strain pattern: a prominent S wave in the left lateral limb leads (reflecting a rightward shift of the QRS axis) together with a Q wave and T-wave inversion in the rightward lead III. This S1Q3T3 pattern is a recognizable clue that points toward acute PE in the right clinical context, even though it isn’t always present.

Understanding why this pattern fits: the embolism raises pulmonary vascular resistance, loading the right ventricle and causing it to dilate and strain. The electrical axis shifts to the right, producing the deep S in lead I and the Q/T changes in lead III. Sinus tachycardia is the most common accompanying rhythm, driven by hypoxemia and sympathetic stimulation.

Other findings described in the distractors align more with other cardiac conditions. Notched P waves with enlarged left atrium point to atrial enlargement from mitral disease. Patterns of QS or monophasic R waves across precordial and lateral leads can indicate myocardial infarction or conduction abnormalities, not the typical acute right-heart strain pattern seen with PE.