Clinical Overview

A Q wave is the first negative deflection of the QRS complex, occurring before any upward (R wave) deflection, and represents the earliest vector of ventricular depolarization as recorded by a given lead. A small, narrow Q wave is a normal finding in many leads, produced by the heart’s ordinary left-to-right depolarization of the interventricular septum. An abnormal (pathological) Q wave is one that exceeds the size expected from those normal septal forces, and it typically means the lead is instead viewing an area of myocardium that has lost its own electrical activity — most often scarred or necrotic tissue from a prior or evolving myocardial infarction — so the lead records the surviving, oppositely-directed forces from the rest of the heart rather than a normal initial deflection of its own. This dataset also carries a separate, similarly-named “Q Wave Abnormal” (QWAb) label. A SNOMED-mapping review of this dataset found that AQW’s underlying code correctly resolves to the “Q wave abnormal” concept, while QWAb’s underlying code resolves to an unrelated concept (a counterclockwise vectorcardiographic loop finding) and is a documented mismapping — so AQW, not QWAb, is this dataset’s validated Q-wave-abnormal label. That does not fully settle why the dataset carries two separate acronyms for the same finding, or whether QWAb’s own records behave identically to AQW’s in practice, so this page treats AQW as its own, independently-sourced finding rather than assuming any particular relationship to QWAb.

Mechanistically, once a segment of myocardium is no longer electrically active — whether from transmural infarction, replacement fibrosis, or infiltrative disease — the lead overlying that segment can no longer record its own depolarization forces. Instead, it records the resultant forces of the rest of the ventricle depolarizing away from it, which appears as a deep or wide negative deflection instead of the small or absent Q wave that segment would otherwise contribute. Published criteria for exactly how large a Q wave has to be before it counts as pathological vary by source: commonly taught thresholds are a duration of 40 ms (1 mm) or more, a depth of 2 mm or more, a depth at least 25% of the following R wave, or any Q wave (or QS complex) in leads V1-V3, present in at least two anatomically contiguous leads (Burns & Buttner, LITFL, 2024). The 2018 ESC/ACC/AHA/WHF Fourth Universal Definition of Myocardial Infarction uses a closely related but stricter threshold for its own diagnostic purpose — a duration of 30 ms or more and an amplitude of 1 mm or more, or a QS complex, in two contiguous leads (Thygesen et al., Circulation, 2018). These remain two genuinely different current reference standards rather than a single settled consensus, reflecting each document’s different purpose (general ECG-morphology teaching versus standardized MI diagnosis); this page uses the more commonly taught thresholds above for its own interpretation guidance.

Clinically, a pathological Q wave most often signals current or prior myocardial infarction and, once established, generally persists indefinitely; if reperfusion (for example, primary PCI) occurs early enough, stunned but viable myocardium can recover and a pathological Q wave can resolve. Absence of a pathological Q wave does not rule out myocardial infarction — many infarctions, particularly non-transmural ones, never produce one. A 2025 study of ST-elevation MI patients treated with primary PCI found that pathological Q waves at presentation were associated with greater thrombus burden and worse post-intervention myocardial perfusion, making their presence a meaningful prognostic signal even in the current era of rapid reperfusion. Not every abnormal Q wave reflects ischemic damage, however: hypertrophic cardiomyopathy, severe left ventricular hypertrophy, cardiac amyloidosis and other infiltrative cardiomyopathies, and ventricular pre-excitation (Wolff-Parkinson-White pattern) can all produce a “pseudo-infarction” Q-wave pattern that mimics an infarct without one being present — cardiac amyloidosis alone has been reported to produce this pattern in roughly 30-70% of affected patients.

An abnormal Q wave itself is an ECG finding, not a symptom-producing event — a patient with an old, stable Q wave from a prior infarction is frequently asymptomatic and may have no history of a recognized cardiac event at all, since a meaningful proportion of myocardial infarctions are clinically silent. When symptoms are present, they arise from whatever underlying process produced the Q wave rather than from the Q wave itself: an acute or evolving infarction typically presents with deep, substernal, visceral chest pain or pressure, often radiating to the arm, jaw, neck, or back, accompanied by dyspnea, diaphoresis, nausea, or vomiting, while a chronic infiltrative or hypertrophic cardiomyopathy may instead present with exertional dyspnea, fatigue, or symptoms of heart failure over a longer course.

Causes and risk factors include prior or acute transmural myocardial infarction (the most common cause), hypertrophic cardiomyopathy (deep, narrow “dagger-like” septal Q waves from disproportionate septal hypertrophy), severe left ventricular hypertrophy with poor precordial R-wave progression, cardiac amyloidosis and other infiltrative cardiomyopathies, ventricular pre-excitation (Wolff-Parkinson-White pattern), and technical causes such as lead misplacement or extreme cardiac rotation that can mimic a true pathological Q wave without underlying disease.

Interpretation Guide

Key Features:

• Rate: not a defining feature — an abnormal Q wave is a morphology finding superimposed on whatever the underlying rate happens to be
• Rhythm: not a defining feature — this finding describes QRS morphology, not the rhythm’s origin or regularity
• P waves: within normal limits; unaffected by the Q wave itself
• PR interval: within normal limits (0.12-0.20 s); a short PR interval should raise suspicion for a pseudo-infarct pattern from ventricular pre-excitation rather than a true infarct-related Q wave
• QRS complex: the defining feature — a Q wave meeting one or more commonly cited pathological criteria (duration ≥40 ms, depth ≥2 mm, depth ≥25% of the following R wave, or any Q wave/QS complex in V1-V3), present in at least two contiguous leads; small, narrow (<40 ms) physiologic septal q waves in leads I, aVL, and V5-V6 are normal and should not be flagged
• ST segment: typically within normal limits for an isolated, chronic Q-wave finding; new or evolving ST-segment elevation or depression accompanying a new Q wave points toward an acute or recent infarction rather than an old, stable scar
• T waves: typically within normal limits for a chronic finding; T-wave inversion accompanying a new Q wave likewise points toward an acute or evolving process
• QT interval: not independently affected by the Q wave itself
• Other findings: poor R-wave progression across the precordial leads is a related, nonspecific finding that can accompany or mimic anterior Q-wave changes; a tall, wide R wave with an R/S ratio ≥1 in V1-V2 functions as the electrical mirror image of a Q wave for a posterior-wall process, since no standard 12-lead electrode directly faces the posterior wall — though this attribution is genuinely disputed: some sources hold to the classic posterior-wall reading, while others argue the pattern more specifically reflects lateral-wall involvement (Goldwasser et al., Annals of Noninvasive Electrocardiology, 2015) [CLINICAL REVIEW NEEDED: posterior-vs-lateral attribution of this R-wave pattern is unsettled between sources]

Comparing a new strip against a prior ECG is the fastest way to tell an old, stable scar from a new event — the Q wave morphology alone cannot make that distinction.

Key Leads

• No single lead defines this finding — which lead or lead group shows the abnormal Q wave depends entirely on which myocardial territory is affected, and the pattern is assessed by contiguous lead groupings rather than any one lead in isolation.
• Leads II, III, aVF – the inferior lead group
• Leads V1-V4 (V1-V3 especially, where any Q wave is considered abnormal) – the anteroseptal lead group
• Leads I, aVL, V5-V6 – the lateral lead group
• Leads V1-V2 (indirect) – no lead directly faces the posterior wall, so a posterior-wall process shows no Q wave here; instead look for the reciprocal tall, wide R wave described above

Differential Diagnosis

• Left Ventricle Hypertrophy (LVH) — severe hypertrophy (including hypertrophic cardiomyopathy) can produce poor precordial R-wave progression, QS deflections in the right precordial leads, or deep but disproportionately narrow (<40 ms) “dagger-like” septal Q waves in I, aVL, and V5-V6 that mimic an infarct pattern; voltage criteria for hypertrophy, and the narrower-than-expected duration of the hypertrophic-cardiomyopathy-type Q wave, both point away from a true infarct-pattern Q wave
• Ventricular Preexcitation (VPE) — the delta wave of ventricular pre-excitation can produce a pseudo-infarction Q-wave pattern, most often mimicking inferior Q waves in II, III, and aVF depending on accessory-pathway orientation; a short PR interval and the slurred delta-wave upstroke at the very start of the QRS (rather than a sharp, well-formed initial deflection) point toward pre-excitation instead of a true infarct-related Q wave
• Anterior Myocardial Infarction (AnMI) — Q waves confined to V1-V4 together with a supporting clinical picture (accompanying ST-segment changes, symptoms, or a documented ischemic event) support the more specific anterior-infarction label rather than an isolated, non-territory-specific abnormal-Q-wave finding; how this dataset’s annotation distinguishes a general abnormal-Q-wave label from its territory-specific infarction labels is not documented
• Myocardial Infarction In The Side Wall (MISW) — Q waves in the lateral leads (I, aVL, V5-V6) together with a supporting ischemic history raise suspicion for myocardial infarction rather than an isolated, non-territory-specific abnormal-Q-wave finding; this dataset’s own SNOMED mapping for the MISW label resolves only to the generic myocardial-infarction concept, not a validated lateral/side-wall-specific one, so a lateral Q-wave distribution should be read as suggestive of MI generally rather than as confirming side-wall localization specifically
• R Wave Abnormal (RWAb) — a tall, wide R wave with an R/S ratio ≥1 in V1-V2 is classically described as the mirror-image counterpart of a Q wave for a posterior-wall infarct, since no standard 12-lead electrode directly faces the posterior wall, though some literature disputes whether this pattern specifically indicates posterior, rather than lateral, involvement (Goldwasser et al., Annals of Noninvasive Electrocardiology, 2015) [CLINICAL REVIEW NEEDED: same posterior-vs-lateral dispute noted in the Interpretation Guide above]

Treatment Brief

An abnormal Q wave found as an isolated finding requires context, not a reflex response — the same morphology can represent a decades-old, stable scar or a new, evolving infarction, and the finding alone cannot distinguish between them.

• Confirm lead placement and repeat the strip if the pattern is new or unexpected, since technical lead misplacement can produce a pseudo-Q-wave pattern.
• Compare against a prior ECG whenever one is available — an unchanged Q wave in an asymptomatic patient is reassuring, while a new Q wave is not.
• Check for accompanying ST-segment or T-wave changes and correlate with symptoms; a new Q wave with ST-segment elevation or depression, T-wave inversion, or chest pain, dyspnea, or diaphoresis warrants prompt provider notification.
• Note whether the Q wave is isolated or accompanied by other findings (a short PR interval, voltage criteria for hypertrophy, or a known history of cardiomyopathy) that would point toward a non-ischemic cause rather than infarction.
• An asymptomatic, unchanged Q wave with no accompanying ST/T changes and a known prior cardiac history generally needs no acute action beyond routine documentation and provider follow-up.