What disorder are pathological waves on an electrocardiogram (EKG) most commonly associated with?

Pathological Q Waves on EKG Are Most Commonly Associated with Myocardial Infarction

Pathological Q waves on an electrocardiogram (EKG) are most commonly associated with myocardial infarction, representing areas of myocardial necrosis and fibrosis. 1

Definition and Characteristics of Pathological Q Waves

• Pathological Q waves are defined as a Q/R ratio ≥ 0.25 or Q waves ≥ 40 ms in duration in two or more contiguous leads (except III and aVR) 1
• According to classic criteria, pathological Q waves appear as:
  • Any Q wave ≥ 0.02 sec or QS complex in leads V2–V3 1
  • Q wave ≥ 0.03 sec and ≥ 0.1 mV deep or QS complex in leads I, II, aVL, aVF or V1–V6 in any two leads of a contiguous lead grouping 1
• These abnormal Q waves typically develop as a result of transmural myocardial necrosis, representing electrically inert myocardium that is incapable of depolarization 2

Pathophysiology of Q Waves in Myocardial Infarction

• Q waves represent the absence of electrical activity in necrotic myocardial tissue 2
• In myocardial infarction, Q waves typically develop after myocardial necrosis has occurred, indicating irreversible myocardial damage 1, 3
• Patients with Q-wave MI have larger infarct size and lower left ventricular ejection fraction (LVEF) compared to non-Q-wave MI patients 3
• Q waves can appear early in the course of acute myocardial infarction, with studies showing that up to 53% of patients admitted within 1 hour of symptom onset already have abnormal Q waves on their initial ECG 4

Clinical Significance and Prognosis

• The presence of pathological Q waves at presentation in anterior ST-segment elevation myocardial infarction (STEMI) is associated with:
  • Higher peak creatine kinase levels 5
  • Greater incidence of heart failure during hospitalization 5
  • Higher in-hospital mortality 5
  • Shorter time to heart failure development within the first year 6
• Q-wave regression may occur in approximately 40% of patients with initial Q-wave MI within 24 months of follow-up 3
• Patients with Q-wave regression show significantly larger LVEF improvement (9% ± 11%) compared to those with persistent Q waves (2% ± 8%) 3

Other Conditions Associated with Pathological Q Waves

While myocardial infarction is the most common cause, pathological Q waves can also be seen in:

• Hypertrophic cardiomyopathy (HCM) 1
• Arrhythmogenic right ventricular cardiomyopathy (ARVC) 1
• Infiltrative myocardial diseases 1
• Accessory pathways 1
• Myocardial fibrosis in the absence of coronary artery disease 1

Evaluation of Pathological Q Waves

• An ECG with abnormal Q waves should be carefully examined for the possibility of an accessory pathway 1
• If pathological Q waves are isolated to leads V1-V2, the ECG should be repeated with careful attention to lead placement, as high lead placement can cause a pseudo-septal infarct pattern 1
• Persistence of pathological Q waves in two or more contiguous leads warrants further investigation with echocardiography to exclude cardiomyopathy 1
• In patients ≥30 years with suspicion of prior myocardial infarction or risk factors for coronary artery disease, stress testing may be warranted 1

Common Pitfalls in Interpretation

• Not all Q waves are pathological - normal septal Q waves are small (<0.03 sec and <25% of the R-wave amplitude) in leads I, aVL, aVF, and V4–V6 1
• A QS complex in lead V1 is normal 1
• A Q wave <0.03 sec and <25% of the R wave amplitude in lead III is normal if the frontal QRS axis is between 30° and 0° 1
• A Q wave may also be normal in aVL if the frontal QRS axis is between 60° and 90° 1
• Lead misplacement can cause pseudo-infarct patterns, particularly high placement of precordial leads causing Q waves in V1-V2 1