What is the Q wave?

Hello, I'm an expert in cardiology with a focus on electrophysiology. I'd be happy to explain what a Q wave is. A Q wave is a specific type of wave seen on an electrocardiogram (ECG or EKG), which is a test that records the electrical activity of the heart. The Q wave represents the initial depolarization of the ventricles, which is the first phase of the heart's pumping action. Normally, Q waves are small and represent the spread of electrical impulses from the endocardium to the epicardium of the heart. However, in certain conditions, particularly in the context of a myocardial infarction (heart attack), Q waves can be quite prominent. Pathological Q waves are deeper and wider than normal and are indicative of tissue damage or death (necrosis) in the heart muscle. The presence of pathological Q waves on an ECG is one of the diagnostic criteria for a previous heart attack. It's important to note that Q waves can also be seen in other conditions that do not involve heart damage, such as left bundle branch block or Wolff-Parkinson-White (WPW) syndrome. Therefore, the interpretation of Q waves must be made in the context of the entire ECG and the patient's clinical history.

The Q wave is the first downward deflection after the P wave and the first element in the QRS complex. When the first deflection of the QRS complex is upright, then no Q wave is present. The normal individual will have a small Q wave in many, but not all, ECG leads.