STEMI posterior

Introduction

Posterior infarction accompanies 15-20% of STEMIs, usually occurring in the context of an inferior or lateral infarction

  • Isolated posterior MI is less common (3-11%) 

  • Posterior extension of an inferior or lateral infarct implies a much larger area of myocardial damage, with an increased risk of left ventricular dysfunction and death

Etiology

Usually caused by posterior descending artery (PDA) occlusion. 

Approximately 70% of the population is “right-dominant” (RCA supplies the PDA), while 10% are “left-dominant (the LCx supplies the PDA), and 20% are “co-dominant” (both the RCA and LCx jointly supply the PDA).

Pathophysiology

Rupture of a coronary artery plaque, thrombosis, and blockage of the downstream perfusion leading to myocardial ischemia and necrosis.

ECG manifestation

Posterior myocardium is not directly visualised by 12-lead ECG, given the placement of anteroseptal leads V1-V3, they are indirectly examining the posterior wall too

  • Horizontal ST depressions V1-V3
  • Dominant R wave (R/S ratio > 1) in V2-V3
  • Large/upright broad R waves (>30ms)
  • Upright T waves V1-V3

Posterior leads: Posterior MI is confirmed by the presence of ST elevation in the posterior leads (V7-9). The degree of ST elevation seen in V7-9 is typically modest – only 0.5 mm of ST elevation is required to make the diagnosis of posterior MI!


Picture 1 Posterior leads
Lead V7: posterior axillary line 
Lead V8: midscapular
Lead V9: paraspinal

https://litfl.com/posterior-myocardial-infarction-ecg-library/


ECG 1 STEMI of posterior wall (ST depressions and upright T waves in V1-V3)

ECG 2 STEMI of posterior and inferior wall (ST depressions in V1-V3, STE in II, III, aVF) 

Management

  • coronary angiography/PCI
  • UFH
  • ASA
  • P2Y12 inhibitors
  • nitrates
  • analgesia
  • 02  

References

  1. Brady W, Erling B, Pollack M, et al. Electrocardiographic manifestations: acute posterior wall myocardial infarction. J Emerg Med 2001;20:391-401
  2. Lizzo JM, Chowdhury YS. Posterior Myocardial Infarction. 2020 Nov 29. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan–. PMID: 31985961.
  3. http://www.emdocs.net/ecg-pointers-posterior-mi/
  4. https://litfl.com/posterior-myocardial-infarction-ecg-library/