In an ECG, what does the term "Q wave" signify?

• A. A normal finding in all ECGs
• B. A pathologic Q wave may indicate a previous myocardial infarction
• C. An indication of pacemaker activity
• D. A sign of atrial enlargement

Answer: (B)

The term "Q wave" in an ECG refers to a specific deflection on the ECG waveform that corresponds to the initial negative deflection of the QRS complex. A pathologic Q wave is particularly significant in clinical practice, as it may indicate that a patient has experienced a previous myocardial infarction (heart attack). When there is damage to the heart muscle due to insufficient blood supply during a myocardial infarction, necrotic tissue can develop, which may manifest as abnormal Q waves on the ECG. These Q waves often suggest that a portion of the heart has been permanently damaged, thus providing crucial information for diagnosis and management of cardiovascular conditions.

Identifying pathologic Q waves helps healthcare professionals assess the history of ischemic heart disease in a patient, guiding further investigation and treatment options. This understanding reinforces the importance of correctly interpreting the various components of the QRS complex during ECG analysis.