Introduction

Inferior MI accounts approximately for  40% of all myocardial infarctions. 

Traditionally, inferior MIs have a better prognosis than those in other regions, such as the anterior wall MI.

The mortality rate of an inferior wall MI is approx. 2% to 9%.

In concomitant right ventricular infarction, patients may develop severe hypotension in response to nitrates and generally have a worse prognosis.

Up to 20% of patients with inferior STEMI will develop significant bradycardia due to second- or third-degree AV block (right coronary artery perfuses the AV node).

Inferior STEMI may also be associated with posterior infarction, which confers a worse prognosis due to increased area of myocardium at risk.

Etiology

• right coronary artery (RCA) via posterior descending artery (PDA) - 80%
• PDA originating from circumflex artery (RCA) - 20%
• In some cases - “wraparound” left anterior descending artery (LAD), producing the unusual pattern of concomitant inferior and anterior ST elevation

‍ECG features

• ST elevation in leads II, III and aVF
• Contralateral depressions the lateral and/or high lateral leads (I, aVL, V5 and V6)

These differences allow for electrocardiographic differentiation between RCA and LCx occlusion:

• The injury current in RCA occlusion is directed inferiorly and rightward, producing ST elevation in lead III > lead II (as lead III is more rightward facing)
• Presence of reciprocal ST depression in lead I
• Signs of right ventricular infarction: STE in V1 and V4R

The injury current in LCx occlusion is directed inferiorly and leftward, producing:

• ST elevation in lead II = lead III
• Absence of reciprocal ST depression in lead I
• Signs of lateral infarction: ST elevation in the lateral leads I and aVL or V5-6

‍

‍Treatment

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

ECG 1 STEMI of inferior wall (STE II, III, aVF, concordant STD in other leads) - proximal occlusion of RCA

ECG 2  STEMI of inferior and posterior wall (STE in II, III, VF, STD in aVL, V1-V3) - occlusion of posterolateral coronary artery

ECG 3 STEMI of inferior wall - proximal RCA occlusion

References

1. Kristian Thygesen, Joseph S Alpert, Allan S Jaffe, Bernard R Chaitman, Jeroen J Bax, David A Morrow, Harvey D White, ESC Scientific Document Group, Fourth universal definition of myocardial infarction (2018), European Heart Journal, Volume 40, Issue 3, 14 January 2019, Pages 237–269.
2. Borja Ibanez, Stefan James, Stefan Agewall, Manuel J Antunes, Chiara Bucciarelli-Ducci, Héctor Bueno, Alida L P Caforio, Filippo Crea, John A Goudevenos, Sigrun Halvorsen, Gerhard Hindricks, Adnan Kastrati, Mattie J Lenzen, Eva Prescott, Marco Roffi, Marco Valgimigli, Christoph Varenhorst, Pascal Vranckx, Petr Widimský, ESC Scientific Document Group, 2017 ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation: The Task Force for the management of acute myocardial infarction in patients presenting with ST-segment elevation of the European Society of Cardiology (ESC), European Heart Journal, Volume 39, Issue 2, 07 January 2018, Pages 119–177, https://doi.org/10.1093/eurheartj/ehx393
3. Warner MJ, Tivakaran VS. Inferior Myocardial Infarction. 2020 Aug 8. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan–. PMID: 29262146.
4. https://litfl.com/inferior-stemi-ecg-library/