ECG criteria
- Notch in the R wave, most commonly on the ascending limb or near the peak, in one or more inferior leads (II, III, aVF)
- Crochetage is more frequently observed with a narrow or only moderately widened QRS, but may be combined with incomplete RBBB and signs of right ventricular overload/remodeling; by itself, it does not replace QRS morphology assessment and echocardiography
- The basic definition does not require a notch in all inferior leads simultaneously: presence in any one of II, III, aVF already satisfies the sign, but presence in two or all three leads increases specificity for ASD
- QRS is typically of normal duration (less than 120 ms) or only mildly prolonged
- Must be distinguished from the typical morphology of complete right bundle branch block (wide QRS with rsR'/RSR' in the right precordial leads) — the presence of such morphology requires separate evaluation rather than automatically ruling out crochetage
- Sensitivity and specificity of the sign for ostium secundum ASD are described in individual clinical studies; reproducibility is moderate in routine practice
What it looks like on ECG
Crochetage is a persistent notch in the R wave, most commonly on the ascending limb or near the peak, in one or several inferior leads (II, III, aVF). The term crochetage originates from the French word crochet meaning "hook" and describes a hook-like notch in the R wave. It appears as a short wave or step that interrupts the smooth upslope and downslope of R.
The amplitude of the R wave itself may be normal, with a narrow or moderately widened QRS. The sign is identified when a notch is present in even a single inferior lead; its presence in two or all three leads (II, III, aVF) increases the specificity of the finding for ASD, but is not a mandatory condition of the definition itself — an isolated notch in a single lead still qualifies as the sign, although it is less specific.
It is important to differentiate true crochetage from similar but etiologically distinct notches:
| Sign | Crochetage | Incomplete RBBB |
|---|---|---|
| Localization | II, III, aVF | V1–V2 (rsR'/rSR') |
| QRS width | usually normal, may be moderately widened | typically less than 120 ms, with typical terminal morphology |
| Morphology | notch on the ascending limb or near the peak of R | slurred or split terminal wave (r') |
| Coexistence | may coexist with incomplete RBBB | may coexist with crochetage |
The sign is best visualized on calibrated recordings at a speed of 25 mm/s and a standard gain of 10 mm/mV — excessively low gain may "blur" a subtle notch.
Mechanism
The mechanism is not fully established. Crochetage is attributed to depolarization features associated with volume overload and remodeling of the right heart chambers, primarily the right atrium and right ventricle, which occur with longstanding left-to-right shunting through an atrial septal defect. It is hypothesized that such overload alters the sequence of right ventricular activation, which may form a notch in the inferior leads. The exact electrophysiological substrate has not been proven; discussions include the contribution of delayed conduction through specific regions of the right ventricular myocardium in the setting of its dilation and remodeling, but a definitive anatomical correlation (e.g., to the outflow tract) has not been established in the literature.
Causes
- Atrial septal defect (secundum type, ostium secundum) is the most thoroughly studied association
- Other conditions causing right ventricular volume overload (certain congenital heart defects)
- Described as an isolated finding in a subset of healthy individuals — not strictly specific
Differential diagnosis
- Incomplete right bundle branch block — characterized by typical rsR'/rSR' morphology predominantly in V1–V2 and a QRS duration of less than 120 ms (exact lower threshold depends on the classification used); crochetage may coexist with incomplete RBBB and is differentiated by the location of the notch and overall QRS morphology rather than mutual exclusion
- Normal QRS notching variant — small notches on the QRS complex without a specific distribution in the inferior leads and without the clinical context of right heart overload
- Chatterjee phenomenon (cardiac memory) — T-wave changes following episodes of ventricular pacing or aberrant conduction, rather than an R-wave notch
- Recording artifact (somatic tremor, 50 Hz mains interference) — irregular small fluctuations across the entire tracing, rather than a stable, reproducible notch in R
Clinical significance and management
Crochetage on its own is not life-threatening and does not require emergency intervention. Its practical significance lies in serving as a "clue" to purposefully screen for an atrial septal defect, especially in young patients with unexplained dyspnea, reduced exercise tolerance, or incidental ECG findings (incomplete right bundle branch block, signs of right ventricular overload, right atrial enlargement).
When crochetage is detected in the inferior leads, the physician should:
- evaluate the ECG as a whole for other signs of right heart volume overload (P pulmonale, right atrial enlargement, incomplete right bundle branch block, right axis deviation)
- refer the patient for echocardiography to rule out an atrial septal defect and assess right heart chamber dimensions
- keep in mind that the absence of crochetage does not rule out a defect, and its presence without a defect can occur in some individuals; the sign is used as an auxiliary rather than an independent diagnostic criterion and may coexist with incomplete RBBB without contradicting the diagnosis
Common interpretation errors
- Confusing crochetage with r' slurring/splitting in V1–V2 in incomplete right bundle branch block
- Assuming that the presence of incomplete RBBB automatically rules out crochetage — the findings can coexist
- Mistaking a recording artifact or noise for a true notch
- Diagnosing an ASD based solely on crochetage without echocardiography
- Believing that a notch in only a single inferior lead cannot be crochetage — this lowers the sensitivity of the finding, although involvement of multiple leads increases specificity
- Searching for crochetage on low-quality recordings or at low gain settings where a subtle notch is physically invisible
1. In which leads is the crochetage sign sought?
Crochetage is sought in the inferior leads II, III, and aVF; the notch may be present in one or several of them, and presence in two to three leads increases specificity.
2. With which congenital heart defect is the crochetage sign most extensively studied?
The crochetage sign is described as an ECG marker associated with atrial septal defect (most commonly ostium secundum).
3. Is it true that crochetage and incomplete RBBB are mutually exclusive findings?
Crochetage (R-wave notch in II, III, aVF) can coexist with incomplete RBBB (rsR' in V1–V2); they are differentiated by location and morphology rather than mutual exclusion.
Frequently asked questions
What is the crochetage sign on the ECG?
This is a persistent notch in the R wave in one or more inferior leads (II, III, aVF), typically with a narrow or moderately widened QRS. Presence in multiple inferior leads makes the finding more specific, but is not mandatory for the definition of the sign itself. The sign may coexist with incomplete RBBB, so these findings should not be considered mutually exclusive. It is described as an ECG marker associated with atrial septal defect.
Is the crochetage sign dangerous?
The sign itself is not dangerous and causes no symptoms. Its significance lies in the fact that it may indicate volume overload of the right heart chambers, for example, in atrial septal defect, which warrants further investigation.
How to distinguish crochetage from incomplete right bundle branch block?
Crochetage is a notch on the R wave in the inferior leads (II, III, aVF); finding it in two or more of them increases specificity. Incomplete right bundle branch block produces the typical terminal rsR'/rSR' morphology in the right precordial leads V1–V2. These signs may coexist on the same ECG.
In which congenital heart defect is crochetage most commonly found?
The association with secundum atrial septal defect (ostium secundum) is the most thoroughly studied. When this sign is detected, it is advisable to refer the patient for echocardiography.
Can crochetage be seen in a healthy person?
Yes, isolated cases of R-wave notching can occur without structural heart disease, which is why the sign is used as an auxiliary rather than an independent diagnostic criterion.
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Related terms
More in the «Phenomena and Eponyms» section
Sources
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice, 6th ed.
- Orlov V.N. Guide to Electrocardiography
- AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, 2009 (general principles of ECG measurements; criteria for the prevalence of crochetage in inferior leads are based on individual clinical studies of ASD and may vary across studies)
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.