Originally published at R.E.B.E.L. EM on November 1, 2015. Reposted with permission.

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ECG interpretation is one of the most important skills to master as an emergency physician, and its interpretation can be very complex and frustrating. ECG manifestations can be very subtle, and sometimes the earliest and only ECG change seen will be reciprocal changes alone. To further complicate this, many patients have the atypical symptoms of nausea/vomiting, weakness, or shortness of breath and not chest pain.

What is the anatomic location of aVL to the heart?

aVL is the only lead facing the superior part of the left ventricle

aVL is the only lead that is opposite the inferior wall of the heart (almost 180 degrees from lead III)

What is the differential diagnosis for reciprocal changes in aVL?

Inferior acute myocardial infarction

Anterior acute myocardial infarction

Left ventricular hypertrophy

Left bundle branch block

Digitalis Use

How good are reciprocal changes in aVL in diagnosing myocardial infarction (MI)?

Can lead aVL give prognostic information for acute MI?

ST depression ≥0.1 mV in 2 or more lateral leads (I, aVL, V5, or V6) are more likely to:

What is the most likely culprit artery in inferior MI?

Right coronary artery (80% of cases): Most likely especially if: ST segment elevation lead III > lead II and ST segment depression in lead I and aVL (> 1 mm) Sens 90%, Spec 71%, PPV 94%, and NPV 70%) (Zimetbaum and Josephson 2003)*

Left circumflex artery (20% of cases)

Conclusion

Reading of the ECG remains a crucial diagnostic and prognostic tool for acute MI, and the earliest finding of an acute MI may be reciprocal changes in lead aVL.

Bibliography

Journal of the American College of Cardiology, no. 7. Barrabés, J A, J Figueras, C Moure, J Cortadellas, and J Soler-Soler. 2000. Prognostic significance of ST segment depression in lateral leads I, aVL, V5 and V6 on the admission electrocardiogram in patients with a first acute myocardial infarction without ST segment elevation., no. 7. http://www.ncbi.nlm.nih.gov/pubmed/10841229 European heart journal, no. 1. Birnbaum, Y, S Sclarovsky, A Mager, B Strasberg, and E Rechavia. 1993. ST segment depression in a VL: a sensitive marker for acute inferior myocardial infarction., no. 1. http://www.ncbi.nlm.nih.gov/pubmed/8432289 BMJ (Clinical research ed.), no. 7341 ( 6). Morris, Francis, and William J Brady. 2002. ABC of clinical electrocardiography: Acute myocardial infarction-Part I., no. 7341 ( 6). http://www.ncbi.nlm.nih.gov/pubmed/11934778 The Journal of the Association of Physicians of India. http://www.ncbi.nlm.nih.gov/pubmed/15656026. Parale, G P, P M Kulkarni, S K Khade, Swapna Athawale, and Amit Vora. 2004. Importance of reciprocal leads in acute myocardial infarction. The New England journal of medicine, no. 10 ( 6). Zimetbaum, Peter J, and Mark E Josephson. 2003. Use of the electrocardiogram in acute myocardial infarction., no. 10 ( 6). http://www.ncbi.nlm.nih.gov/pubmed/12621138