ECG Rounds Answer

Diagnosis: Acute cor pulmonale caused by pulmonary embolism (S₁Q₃T₃ pattern).

Pulmonary embolism ranges from incidental, clinically unimportant thromboembolism to massive embolism with sudden death. Acute pulmonary embolism causes elevated pulmonary artery and right heart pressures and decreased cardiac output, which will be reflected in the ECG by the S₁Q₃T₃ pattern. However, when the ECG changes persist even after the pulmonary artery pressure and the right heart size have returned to normal, additional mechanisms are involved,¹ including the release of catecholamine or histamine at the cellular level.^2,3

This patient's ECG shows: sinus tachycardia (with a rate of 100/min), S wave in lead I,Q wave in lead III, and T-wave inversion in lead III (S₁Q₃T₃ pattern); Q waves are also seen in leads II and aVF; T-wave inversion is seen in leads V₁ through V₄ (anterior leads); complete right bundle-branch block (RBBB); and ST-segment depression in leads V₄ through V₆. These findings make this ECG very suspicious for pulmonary embolism. A computed tomography scan of the chest with contrast showed large bilateral pulmonary embolisms.

The S₁Q₃T₃ pattern was first described in 1935,⁴ and transient RBBB was first described in 1939.⁵ However, the S₁Q₃T₃ pattern varies in about 12% to 50% of cases and is therefore not pathogonomic.³ This pattern will resolve within 14 days of onset of disease. Up to 25% of patients with pulmonary embolism have normal ECG at admission.⁶ Transient RBBB is seen in 6% to 67% of patients with pulmonary embolism.¹ ST elevation or depression is seen in up to 50% of this type of patients.⁷ T-wave inversion, diffuse or in the inferior leads, is a frequent finding in pulmonary embolism and is a sign of massive disease; however, good prognostic value has been reported when the T-wave inversion is reversed before the sixth day.⁶

Our patient's ECG had all these findings, making this ECG a prototype for pulmonary embolism as described in the literature. However, the sensitivity and specificity of ECG changes in pulmonary embolism are 26.7% and 57.1%, respectively, and are therefore not sufficient for the diagnosis.¹

Other ECG abnormalities described in the literature include rhythm disturbances, such as sinus tachycardia (8%-69%), first-degree AV block (1%-12%), premature atrial or premature ventricular beats (4%-23%), atrial fibrillation (18%) and atrial flutter (35%), and P-pulmonale (2%-31%)¹; as well as PR depression and low-voltage complexes⁷

References

1. Chan TC, Vilke GM, Pollack M, et al. Electrocardiographic manifestations: pulmonary embolism. J Emerg Med. 2001;21:263-270.
2. Yoshinaga T, Ikeda S, Nishimura E, et al. Serial changes in negative T waves on electrocardiogram in acute pulmonary thromboembolism. Int J Cardiol. 1999;72:65-72.
3. Ferrari E, Imbert A, Chevalier T, et al. The ECG in pulmonary 80 case reports. Chest. 1997;111:537-543.
4. Palla A, Petruzzelli S, Donnamaria V, et al. The role of suspicion in the diagnosis of pulmonary embolism. Chest. 1995;107(1 suppl):21S-24S.
5. Durant TM, Ginsberg IW, Roesler H. Transient bundle branch block and other electrocardiographic changes in pulmonary embolism. Am Heart J. 1939;17:423-430.
6. Sreeram N, Cheriex EC, Smeets JL, et al. Value of the 12-lead electrocardiogram at hospital admission in the diagnosis of pulmonary embolism. Am J Cardiol. 1994;73:298-303.
7. Petruzzelli S, Palla A, Pieraccini F, et al. Routine electrocardiography in screening for pulmonary embolism. Respiration. 1986;50:233-243.