Case Review: Posterior ECG - Why Bother?

 

 

This case review will discuss the role of the posterior ECG in relation to patients suffering from an acute episode of chest pain.

The patient in question was a 72 year old man, whose wife had called 999 after discovering her husband had been suffering from an ongoing episode of central chest pain. The patient had a history of angina and hypertension and was on several cardiac related medications including a glyceryl trinitrate spray, which he had used several times prior to our arrival. Utilising the SOCRATES pain assessment tool (Fisher et al. 2013), I established that the patient was suffering from an episode of crushing central chest pain, which came on at rest, radiated to his left shoulder and had started approximately 20 minutes prior to our arrival. The patient scored the pain 7 out of 10. He also appeared pale and diaphoretic. This history would be consistent with that of an acute coronary syndrome (Map of Medicine, 2014).

 

A 12 lead ECG was obtained which showed isolated ST segment depression in leads V2-V4, similar to the ECG shown below (2011).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ST segment depression can be indicative of a multitude of conditions, including myocardial ischemia (Houghton and Gray, 2014). However isolated ST depression in leads V1-V4 could also be indicative of an isolated posterior STEMI, being that these anterior leads would show reciprocal changes. A clinical review by Morris and Brady in the British Medical Journal suggests that a posterior ECG should be performed to rule out an isolated posterior STEMI (2002). A posterior ECG involves the application of three extra electrodes to evaluate electrical activity on the posterior wall of the left ventricle (Pilbery, 2013). Leads V4,V5 and V6 are removed and attached to electrodes V7,V8 and V9 as shown below. V8 is placed in the midscapular line, V9 is placed just to the left of the spine and V7 is placed between V6 and V8 all at the level of the 5th intercostal space.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The incidence of an isolated posterior STEMI is between 3-7% (Khan et al. 2012), however it should be noted that this data is over 15 years old and therefore one could question its current validity (Melendez, Jones and Salcedo, 1978; Oraii et al. 1999). In line with local guidance the ECG was sent via telemetry to the nearest coronary care unit (CCU) to discuss acceptance. The CCU decided that the patient was not suitable for direct admission to their department and therefore they suggested our patient was to be conveyed to the emergency department.

 

Further management included the administration of morphine sulphate and paracetamol by the paramedic. Studies have shown that paracetamol and morphine work synergistically when used together (Zeidan et al. 2014). Wyatt et al. suggest that intravenous opioid analgesia should be part of the treatment in acute coronary syndromes (2012). However interestingly one retrospective paper looking at non–ST-segment elevation acute coronary syndromes (NSTEACS) suggested that there was a higher in-hospital mortality associated with the use of intravenous morphine (Meine et al. 2005). This raises an interesting question with regards to UK paramedic administration of morphine in suspected cases of NSTEACS, in lieu of a suitable alternative. A pre-alert was also passed to the emergency department.

 

In conclusion, prior to seeing this patient in clinical practice I had heard of the posterior ECG but did not truly understand its rule in identifying a unique STEMI presenatation. Discussing the patient with colleagues I believe the posterior ECG is not a commonly practiced skill, at least within my own clinical practice area. The aim of this case review was therefore to raise awareness of this simple diagnostic tool. I am confident that had the posterior leads shown any ST elevation the patient would have been accepted by the CCU for immediate treatment. I would suggest that reading some of the articles below would enhance ones knowledge and confidence around isolated posterior STEMI recognition and management. Further reading after this incident also led me to conclude that serial recording of ECGs whilst en route to the emergency department to spot an evolving STEMI would have been entirely appropriate in this incident.

 

 

I hope you enjoyed this case review and I welcome your feedback.

 

David

 

 

Steve Smith has written an interesting blog post discussing limitations of posterior leads and therefore it is important to remember local policy will dictate the correct receiving hospital for this patient, I believe in some areas of the UK it would have been entirely appropriate to take this patient directly to the cardiac team -

 

 

Anonymity – Details have been changed and/or omitted above to protect patient confidentiality.

 

 

References & Further Reading

 

Fisher, J., Brown, S. and Cooke, M., Walker, A., Moore, F. and Crispin, P. (eds) (2013) Joint Royal Colleges Ambulance Liaison Committee - UK Ambulance Services Clinical Practice Guidelines 2013. Bridgwater: Class Professional Publishing Ltd.

 

Houghton A. R. and Gray, D. (2014) Making sense of the ECG A hands on guide. 4th edn. Boca Raton: CRC Press.

Khan, J.N., Chauhan, A., Mozdiak, E., Khan, J.M. and Varma, C. (2012) ‘Posterior myocardial infarction: are we failing to diagnose this?’Emergency Medical Journal, 29, pp.15-18. doi:10.1136/emj.2010.099861.

 

Map of Medicine (2014) Acute Coronary Syndromes (ACS) – Suspected. Available at: (Accessed: 13 September 2015).

 

Meine, T.J., Roe, M.T., Chen, A.Y., Patel, M.R, Washam, J.B., Ohman, E.M., Peacock, W.F., Pollack, C.V., Gibler, W.B. and Peterson, E.D. (2005) ‘Association of intravenous morphine use and outcomes in acute coronary syndromes: results from the CRUSADE Quality Improvement Initiative.’ American Heart Journal, 149(6), p.1043-1049.

 

Melendez, L.J., Jones, D.T. and Salcedo, J.R. (1978) ‘Usefulness of three additional electrocardiographic chest leads (V7, V8 and V9) in the diagnosis of acute myocardial infarction.’ Canadian Medical Association Journal, 119(7), pp.745-748.

 

Morris, F. and Brady, W. J. (2002) ‘ABC of clinical electrocardiography: Acute myocardial infarction – Part I’ British Medical Journal, 324 (831). doi:

 

National Institute for Health and Care Excellence (2010) Chest pain of recent onset: Assessment and diagnosis of recent onset chest pain or discomfort of suspected cardiac origin. Available at: (Accessed: 13 September 2015).

 

Oraii, S., Maleki, M., Tavakolian, A.A., Eftekharzadeh, M., Kamangar, F. And Marhaji, P. (1999) ‘Prevelance and outcome of ST-segment elevation in posterior electrocardiographic leads during acute myocardial infarction.’ Journal of Electrocardiology, 32(3), pp.275-278.

Pilbery, R. (2013) ‘Cardiovascular Emergencies’ in Fellows, B. Pilbery, R. Pollak and A. N. Caroline, N. L. Emergency care in the streets. 7th edn. Bridgwater: Jones & Barlett Learning.

 

Posterior MI Standard Leads (2011) [Electrocardiogram]. Available at: (Accessed: 13 September 2015).

 

Wyatt, J. Illingworth, R. N. Graham, C. A. Hogg, K. (2012) Oxford Handbook of Emergency Medicine. 4th edn. New York: Oxford University Press.

 

Zeidan, A. Mazoit, J.X. Ali Abdullah, M. Maaliki, H. Ghattas, T. And Saifan, A. (2014) ‘Median effective dose (ED₅₀) of paracetamol and morphine for postoperative pain: a study of interaction.’ British Journal of Anaesthesia, 112(1), p.118-23. doi:10.1093/bja/aet306.