Emotion can affect the ECG two ways:

• Firstly, by causing asymptomatic ECG changes, leading to an erroneous diagnosis of heart disease. These changes are limited to ST/T wave changes (i.e. not involving the development of a Q wave, or changes to the QRS complex).
  
• Secondly, much more rarely, by causing ‘organic’ cardiac disease, such as ‘standard’ myocardial infarction, arrhythmias or the syndrome of transient left ventricular dysfunction.

An extraordinary common difficult problem in clinical practice is to decide whether an abnormal ECG reflects cardiac pathology or not, with the ECG changes being explained by anxiety or hyperventilation.

Anxiety can profoundly alter the ECG, probably via changes in autonomic nervous system function, as evidenced by the ECG normalizing with manoeuvres that normalize autonomic function (reassurance, rest, and anxiolytics and beta-blockers), with catecholamine infusion producing similar ECG changes. The ECG changes in anxiety are:

• ST flattening, the commonest finding.
  
• Frank ST depression; not rare, especially in hyperventilation.
  
• T wave inversion

How does one differentiate anxiety-induced changes from those reflecting cardiac disease? Fully assessing demographics (age, sex, etc.) and symptomatology are the keys to a correct diagnosis. Though one can often be fairly confident that some patterns are due to anxiety, one cannot always be 100% certain, so it is not uncommon to undertake further limited investigations to exclude heart disease, always explaining beforehand that the result is likely to negative, and the test is required only for reassurance.