Monday, 15 October 2007

Serial ECGs and Non ST Myocardial Infarction (NSTEMI)

Today's Blog is about the simple use of ECGs to make a diagnosis of Non-ST Elevation MI (NSTEMI).

Patients with a myocardial infarction can typically give the following history:

  • Sudden onset central chest pain
  • Worst pain ever in their life e.g. 10/10
  • The pain is described as squeezing / a tight band / like someone sitting on their chest
  • Pain may be epigastric in location
  • Pain may radiate to neck / jaw / shoulder or down either arm although classically on the left side
  • There is usually associated nausea, vomiting, sweatiness and breathlessness.
  • Patients can collapse due to sudden dysrrhythmia
However, patients can present only with sudden onset breathlessness and no chest pain. These patients are typically diabetics.

Hence, it may be impossible to obtain an MI history despite asking all the above important questions.

Examination may or may not be helpful. Acute onset heart failure is often a clue.

On admission to hospital, the cardiac enzymes may be normal. These may sometimes be of no help acutely in MI as they take several hours to rise. However, they should still be performed on admission as they provide a baseline level and if the history is more than several hours, the enzymes may have already become positive.

The, perhaps, most useful and simple non-invasive tool is the ECG. It may sometimes be initially normal only later to show changes.

Therefore, in such cases it is essential to repeat the ECGs and compare them to previous ones such as admission ECGs or even previous ECGs taken some point in the past.

Such changes are usually non-specific T wave inversion and sometimes Q waves. These signify possible myocardial damage.

As I have mentioned in a recent blog article, it is often necessary to perform a Troponin T test despite normally looking CK and CK-MB fractions especially after 6 hours.

For example, a recent case of a patient admitted with breathlessness with a background of chronic renal failure, old MI and diabetes mellitus had no chest pain or other symptoms of AMI. The patient had recently been having intake of more fluid than normal and had not had haemodialysis in several days. Hence, the heart failure that was found on examination and seen on chest X-ray was assumed to be due to fluid overload.
However, when one looked at the ECGs, the initial ones showed a tachycardia. But several hours later the T waves had inverted thoughout all the anterior and a few inferior leads suggestive of wide spread ischaemia likely due to a left main stem lesion.
Echocardiogram showed an EF% of 40% and generalised hypokinesis.

The CK level was only mildly elevated and CK MB was normal. However, after several hours the CK was further raised followed by the CK-MB and AST. A Troponin T test was then requested.

In patients with Chronic Renal Failure / Diabetes they have an increased cardiovascular risk and patients developing breathlessness should not just be assumed to have fluid overload before completely excluding AMI. In such patients checking serial ECGs and Cardiac Enzymes is essential.

Treatment for AMI (NSTEMI) in the acute phase [within 24 hours] include:
  • Aspirin
  • Clopidogrel (recently introduced into Japan but used for several years in Western Europe; 300mg orally followed by 75 mg daily)
  • Statin Therapy e.g. Simvastatin 40mg / Atorvastatin 10mg even if the cholesterol is normal. Statins have been shown to help stabilise plaques and improve the outcome of coronary artery intervention. It is regarded as an acute treatment to be started the same day.
  • Beta-blocker e.g. iv beta blocker followed by oral e.g. bisoprolol / carvedilol / metoprolol unless patient has asthma / COPD / Severe heart failure. Beta blockers have been shown to reduce mortality post-MI. They should be started the same day.
  • ACE-Inhibitor e.g. Ramipril. These should alse be started the same day. They help myocardial remodelling and in heart failure reduce the readmission rate and improve survival.
  • Heparin / Low Molecular Weight Heparin to be continued for 48 hours after pain has settled.
The above is the basic standard for AMI treatment (see the European Resuscitation Council Guidelines 2005)

Remember: ECG can be normal. CK and CK-MB can be normal. Troponin-T can be positive and still be an NSTEMI. You must have a high index of suspicion. Also, please use the TIMI scoring system which ranks people into High or Low Risk and such High Risk patients still require investigation and workup for coronary disease.

Please consider.