A Subtle Sign of Something Sinister…

ECG Exigency 007

A 65-year old man presents to ED at 1am with 90 minutes of central chest pressure that awoke him from sleep. He says he thinks he has ‘indigestion’. The pain is non-radiating, with mild shortness of breath but no nausea, vomiting or diaphoresis. He is an ex-smoker with a 20 pack-year history. There is no previous history of IHD, diabetes, hypertension or high cholesterol.
On arrival he looks well, with normal heart rate (54 bpm), blood pressure (127/86) and oxygen saturations (98% on room air). His pain has improved slightly with sublingual nitrates in the ambulance, although he still has some ongoing chest discomfort. His ECG is shown below:

Q1. Can you describe the ECG?

The ECG shows:

  • Sinus rhythm at 54 bpm
  • Normal axis
  • Normal intervals
  • Borderline left atrial enlargement with a bifid P wave in lead II (P mitrale) and enlargement of the terminal negative portion of the P wave in V1
  • Essentially normal ST segments and T waves, except for some non-specific T-wave flattening in aVL
  • Inverted U waves in the lateral leads I, V5 and V6 (and possibly also in leads II and III)

Inverted U waves in V5 and V6

Q2. What is the significance of these ECG findings?

The most important finding on this ECG is the inverted U waves in the lateral leads.

In patients presenting with chest pain, inverted U waves:

  • Are a very specific sign of myocardial ischaemia
  • May be the earliest marker of unstable angina and evolving myocardial infarction
  • May be observed during attacks of Prinzmetal angina
  • Have been associated with  LAD or LMCA occlusion and the presence of left ventricular dysfunction
  • U wave inversion tends to occur mainly in the lateral leads (I, aVL, V5-6) and may be seen either during ischaemic symptoms or at rest.

With this patient’s history, the U wave inversion would be strongly suggestive of an acute coronary syndrome (unstable angina or NSTEMI).

Inverted U waves may also be seen in:

  • Hypertension
  • Valvular heart disease
  • Congenital heart disease
  • Cardiomyopathy
  • Hyperthyroidism

Examples of U Wave Inversion

Inverted U waves in a patient with unstable angina.

From Girish et al. (click for source)

Inverted U waves in a patient with Prinzmetal’s angina

From Pérez Riera et al. (click for source)

Q3. How would you manage this patient?

  • This patient needs to be managed as an acute coronary syndrome with analgesia, nitrates, oxygen, aspirin, clopidogrel and low-molecular-weight heparin (enoxaparin)
  • At this stage there are no indications for thrombolysis or emergent PCI
  • He will need serial ECGs and troponins to look for evidence of infarction
  • He needs to be admitted under a cardiology team to a monitored bed for further investigation (e.g. angiography)

Q4. Can you guess what happened next?

  • This was a difficult case to sell to cardiology, as the initial troponin I was equivocal (0.05 ng/mL at 2 hours) and the cardiology registrar was dubious about the significance of the ECG changes.
  • The patient ended up spending the night in ED in a monitored bed.
  • Serial cardiac enzymes confirmed a NSTEMI, with a troponin I of 0.87 ng/mL at 6 hours and 4.0 ng/mL at 12 hours.
  • Serial ECGs remained unchanged throughout his hospital stay – the lateral U wave inversion persisted and there was no progression to ST segment elevation or depression.
  • In the morning, he was transferred to a CCU bed under the care of a cardiologist, with angiography planned for the following day.

References

  • Gerson MC, McHenry PL. Resting U wave inversion as a marker of stenosis of the left anterior descending coronary artery. Am J Med. 1980 Oct;69(4):545-50. PMID: 7424944
  • Girish MP, Gupta MD, Mukhopadhyay S, Yusuf J, Sunil Roy TN, Trehan V. U wave: an important noninvasive electrocardiographic diagnostic marker. Indian Pacing Electrophysiol J. 2005 Jan 1;5(1):63-5. PMID: 16943944
  • Pérez Riera AR, Ferreira C, Filho CF, Ferreira M, Meneghini A, Uchida AH, Schapachnik E, Dubner S, Zhang L. The enigmatic sixth wave of the electrocardiogram: the U wave. Cardiol J. 2008;15(5):408-21. Review. PMID: 18810715
  • Sovari AA, Farokhi F, Kocheril AG. Inverted U wave, a specific electrocardiographic sign of cardiac ischemia. Am J Emerg Med. 2007 Feb;25(2):235-7. PMID: 17276833
  • Zimmerman FH. Clinical Electrocardiography: Pre-Test Self-Assessment and Review, McGraw-Hill 1994.
  • Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
  • Wikipedia. The U Wave. http://en.wikipedia.org/wiki/U_wave
For more great ECG cases see the ECG library or ECG clinical case library

http://lifeinthefastlane.com/ecg-library/basics/u-wave/

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Comments

  1. says

    Thanks for breaking down EKG basics to bite sized portions for students like me who do not do too well with them. Now the only problem is that I will start seeing inverted U waves in all chest-pain-EKGs that I now see! :( Time to go back to the basics again, I guess!

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