AUTHORS

Joseph Moran, MD and Dr. Daniel Coleman, MD

CASE

A middle-aged male presented in cardiac arrest. He had reportedly complained of preceding chest pain. Upon EMS arrival, his presenting rhythm was ventricular fibrillation (VF), which was refractory to multiple attempts at defibrillation. After receiving treatment for refractory VF, the patient had return of spontaneous circulation (ROSC). He was hypotensive, and ultimately required triple pressor support to maintain adequate mean arterial pressure. An initial electrocardiogram (EKG) was performed, which showed sinus tachycardia. A repeat EKG was performed one hour later, showing:

The providers quickly performed another EKG:

DIAGNOSIS

Posterior ST-segment elevation myocardial infarction (STEMI)

DISCUSSION

Posterior MI is caused either by occlusion of the left circumflex coronary artery or the posterolateral branch of the right coronary artery. The characteristic EKG changes may include a large, broad R wave, ST depression, and upright T wave in leads V1-V3. A posterior MI is confirmed by using leads V7-V9, which are placed on the patient’s back for a direct “view” of the posterior myocardium.[1] Thus, any EKG showing ST depressions in V1-3 should immediately prompt a second EKG that includes V7-V9, and not merely assumed to be anterior wall ischemia. Alternatively, you may perform the “flip test” by turning over the EKG and holding it in front of a light, at which point the ST depressions in V1-V3 take on the more familiar (and concerning) tombstone morphology. The correlation between these anterior ST depressions and posterior ST elevations is not perfect, however, so an EKG with posterior leads should still be performed.[2]

In this case, the EKG that was performed one hour after ROSC clearly shows ST depressions in V1-V3, but you can also see the beginning of an ST elevation in V6, the most lateral lead in a routine EKG. The repeat EKG included V7-V9 (V4 is lead V7, although not marked as such), and clearly demonstrates ST elevations consistent with a posterior MI.

CASE RESOLUTION

Ultimately, given the patient’s pressor requirement and extremely guarded prognosis, a goals of care discussion was held with the family, who opted to make the patient comfort measures only. He subsequently passed peacefully in the emergency department.

TAKE-AWAYS

• Any EKG with ST depressions in V1-V3 should be concerning for a posterior MI.

• Concern for posterior MI should immediately prompt a repeat EKG with V7-V9.

FACULTY REVIEWER

Dr. Antholy Napoli

REFERENCES

1. Chizner MA. Acute Myocardial Infarction and Its Complications: Clinical Spectrum, Diagnosis, and Management. Cedar Grove, NJ: Laennec Publishing, Inc.; 1996. 859-860. (Chinzer MA, editor. Classical Teachings in Clinical Cardiology.)

2. Agarwal J, Khaw K, Aurignac F, LoCurto A. Importance of posterior chest leads in patients with suspected myocardial infarction, but nondiagnostic, routine 12-lead electrocardiogram. Am J Cardiol. 1999;83(3):323-326.