Q waves and QS complexes

A Q wave or a QS complex on the electrocardiogram (ECG) is usually considered as the sign of an old myocardial infarction. While this is often true, the physician should not forget that other possibilities may exist, particularly in the elderly, for example, left ventricular hypertrophy (LVH) (including hypertrophic obstructive cardiomyopathy [HOCM]), cardiac amyloidosis, left intraventricular conduction disturbance, aberrant ventricular activation (WPW pre-excitation pattern). A QS complex in the limb leads or a Q wave in the precordial leads are sometimes the result of mistaken positioning of the electrodes. Furthermore, a Q wave in the inferior limb leads can sometimes disappear on deep inspiration. Similar changes may rarely be seen in normal subjects.