National Physical Therapy Examination (NPTE) Practice Exam

Significant Q waves on an electrocardiogram are indicative of myocardial infarction, or a heart attack. When a part of the heart muscle becomes damaged or dies due to inadequate blood supply, it leads to changes in the heart's electrical activity, which can manifest as Q waves on an ECG. These Q waves signify that there has been necrosis of the myocardial tissue, which is a hallmark of a previous myocardial infarction.

In the context of the other options, premature atrial complexes are characterized by early atrial contractions but do not cause significant Q wave changes. Supraventricular tachycardia reflects an increased heart rate originating above the ventricles and does not typically show Q wave alterations. Atrial fibrillation presents with an irregularly irregular rhythm but does not produce significant Q waves either. Therefore, significant Q waves are most closely associated with the history of myocardial infarction, emphasizing the importance of interpreting these changes accurately in clinical practice.