Q wave

A Q wave is the first downward dip of the QRS complex, occurring right before the tall upward R wave. Small Q waves are a normal part of many heartbeats and simply reflect the very first direction the electrical wave takes through the ventricles. On their own they are usually nothing to worry about.

What draws attention is the pathologic Q wave — one that is unusually deep or wide. Such a Q wave often means that a region of heart muscle was damaged in the past, typically by an old heart attack. Dead or scarred muscle no longer generates its own electrical signal, so the leads facing that area instead pick up the signal travelling away from them, recorded as a prominent downward deflection.

Because pathologic Q waves tend to be permanent, they can serve as a lasting electrical fingerprint of a previous infarction, sometimes the first hint that a silent event occurred. They are read with care, since not every deep Q wave reflects old damage; their width, depth, and the leads in which they appear all matter, and they are interpreted alongside the clinical history and other findings.