Q: Given what we know so far, what is the most likely cause of the ST segment elevation in leads V1 and V2?
- Brugada syndrome
- Pulmonary embolism
- Right ventricular injury
- Anterior myocardial infarction
A: The correct answer is right ventricular injury (discussed below).
Brugada syndrome is a genetic disorder caused by a mutation in the cardiac sodium channel gene. It is characterized by a pronounced elevation of the J point, a coved-type ST segment elevation in leads V1 and V2, and a propensity to develop malignant ventricular arrhythmias and sudden cardiac death.
In this patient, the pattern of ST segment elevation in leads V1 and V2 may be falsely interpreted as the classic type 1 Brugada electrocardiographic pattern. However, the classic type 1 Brugada electrocardiogram is characterized by a coved ST elevation followed by a negative T wave.1 The absence of T-wave inversion following ST segment elevation in this patient excluded Brugada syndrome. Moreover, the main presentation in patients with Brugada syndrome is either syncopy or sudden cardiac death.
Pulmonary embolism can present with various electrocardiographic patterns. ST segment elevation in the antroseptal leads is an extremely rare sign and has been demonstrated in a few reports.2,3 Pulmonary embolism can also present with abnormal Q waves in leads III and aVF but not in lead II.4 The initial electrocardiographic rhythm in patients who present with cardiac arrest is usually pulseless electrical activity; however, the combination of increased right ventricular oxygen consumption due to increased right ventricular afterload and right ventricular hypoperfusion due to hypotension can lead to right ventricular ischemia and subsequent arrhythmias. Mittal and Arora5 described a case of submassive pulmonary embolism with right ventricular infarction presenting with sustained ventricular tachycardia.
The prognosis is usually poor in patients with cardiac arrest due to pulmonary embolism, which is usually caused by a massive embolus and usually necessitates thrombolytic therapy.
In the patient described here, pulmonary embolism was part of the differential diagnosis, given the presence of ST segment elevation in leads V1 and V2 in the context of the clinical scenario. However, the restoration of spontaneous circulation without any specific treatment for pulmonary embolism and the normal oxygenation after cardiac arrest excluded pulmonary embolism.
Right ventricular myocardial injury is important to recognize for therapeutic and prognostic reasons. It is usually associated with inferior infarction because it is typically secondary to an acute occlusion of the proximal right coronary artery proximal to the take-off of the right ventricular marginal branch. In the described scenario, the presence of ST segment elevation and Q waves in the inferior leads together with reciprocal ST segment depression in leads I and aVL represents an inferior myocardial infarct. ST segment elevation in the right precordial leads V3R and V4R is a marker for right ventricular injury—especially in V4R, in which it is a powerful predictor of right ventricular involvement. ST segment elevation in leads V1 and V2 is not usually demonstrated in patients with right ventricular injury because the electrical current of injury from the left ventricle inferior myocardial infarction dominates the right ventricular electrical forces, blocking the appearance of ST segment elevation in these leads.6 Data from the Hirulog and Early Reperfusion or Occlusion-2 trial showed that ST segment elevation of 1 mm or greater in lead V1 is associated with an increased risk of death in patients with acute inferior myocardial infarction.7 Furthermore, the presence of ST-segment elevation in lead V6 in patients with acute Q-wave inferior myocardial infarction, as evident in the first electrocardiogram, is associated with larger infarct size and a greater incidence of major arrhythmias.8
DETERMINING THE CULPRIT VESSEL
In the scenario described here, differentiating between right ventricular injury and anterior myocardial infarction is important to determine the culprit vessel.