Duration and amplitude of Diagnostic Q Waves: at least 40 milliseconds in duration, at least 25% of the amplitude of the following R wave and they must occur in two adjacent or contiguous leads. If not all criteria are met, the Q waves are non-diagnostic.
Septal infarcts are associated with diagnostic Q waves in V1and V2. While a QS pattern in V1-2 usually is associated with a septal infarct, it can occur with anatomic changes (vertical axis) due to lung disease or LVH and with intraventricular conduction defects such as LAFB, LBBB, and WPW or with hypertrophic cardiomyopathy.
With the exception of errors of techniques, the genesis of the QS pattern in leads V1 and V2 in individuals without myocardial infarction or other forms of myopathy is due to altered orientation of the initial septal vector. The conditions that alter the main vector include: 1) spurious change of order of septal depolarization; 2) change in anatomical orientation due to rotation, displacement, or both and 3) abnormalities of intraventricular conduction.
If this is a new pattern and the patient is presenting with typical ischemic chest pain and ST elevation, then ASA and thrombolysis should be given as soon as possible unless there is a contraindication.
While a QS pattern in leads V1 and V2 can be associated with myocardial infarction, there are patients in whom this pattern appears in the absence of any heart disease. The possibility that a QS pattern in leads V1 and V2 is due to altered direction of septal forces or is due to faulty recording technique should be considered when the pretest likelihood for infarction is low and there is no supporting evidence for myocardial infarction. The ECG should be carefully examined for other patterns that explain the Q waves.
If the history does not suggest a MI or another explanation, the ECG should be repeated with anatomically correct electrode placement. If the patient has pulmonary disease as an explanation, other ECG findings of lung disease should be present. The diagnosis of septal infarction should not be made if left anterior fascicular block (LAFB), left bundle branch block (LBBB) or Wolff-Parkinson-White syndrome (WPW) are present.
View an ECG Example