In Cardiology, What Are Q Waves?

The heart generates three major wave groups of electrical impulses, the second group containing Q waves when they are present. The first wave of this group, the P wave, is concentrated in the upper heart, or atrial area. The second wave group, the QRS complex, is concentrated in the lower heart, or ventricular area. The third wave group consists of the T wave, which is mainly a state of rest for the heart before generating a new set of wave impulses.

The Q wave is the initial and lowest wave of the QRS complex, with the R wave being the peak, and the S wave being the lower ending point. These Q waves are also known as septal waves, because they arise in the interventricular septum during contraction of the lower heart muscles, or ventricular myocardium. Wave characteristics can be shown by using an electrocardiogram (EKG or ECG) to record heart activity.

An EKG uses padded electrodes placed on the skin to read the electrical impulses generated by the heart. When the impulses move toward an electrode, it is termed a positive deflection; when the impulses move away from the electrode, it is said to be a negative deflection. A QRS complex is normally picked up by an EKG as five deflections, and a Q wave is typically considered to be the deflection that turns downward just after the P wave occurs.

EKGs are widely used to help diagnose heart conditions, such as by indicating the presence of pathologic Q waves. This type of wave is the deviation or absence of a normal Q wave repeating pattern in the QRS complex; this can mean these waves are not being generated or are flawed because of scarring of the heart muscle from a heart attack, or myocardial infarction. Although the ventricular myocardium has been known to heal after a myocardial infarction in this area, which could cause the pathologic waves to disappear, Q waves created by an infarction usually last for the rest of a person’s life.

EKGs are an essential aid in helping to diagnose currently occurring myocardial infarctions; these can record any rise in the wave pattern of ST segments, waves occurring after the QRS complex. Pathologic Q waves occur after the event has ended, so they cannot show a current myocardial infarction; however, deep wide waves seen on an EKG in the right place can help to indicate a current or evolving myocardial infarction. Magnetic resonance imaging (MRI) has also been used to help locate areas of heart scarring in patients with known previous myocardial infarctions.