ECG criteria
- The baseline (TP segment) is covered with small, irregular notches rather than being flat
- Lead distribution is inconsistent: the muscle artifact is often more prominent in limb leads, but may also be pronounced in precordial leads — this in itself is not a diagnostic criterion
- The oscillations usually lack a stable phase relationship with the QRS complex and may change with relaxation, patient movement, or changes in electrode contact
- True P waves, QRS complexes, and T waves can be traced through the interference upon careful inspection
- The artifact increases with tremors, shivering response, motor restlessness, and decreases when the patient's muscles are at rest
- Clinically, the patient often presents with hypothermia (low core body temperature) and visible muscle shivering
- A possible, but non-specific, accompanying sign is the Osborn wave at the J point, which is more commonly associated with hypothermia, but also occurs in other conditions; it cannot be used in isolation for diagnosis and must be distinguished from the artifact itself
What it looks like on ECG
Against the background of a true heart rhythm, the baseline and sometimes the complexes themselves are covered with frequent fine notches — resembling a "sawtooth" or "fringe". The oscillations are irregular in amplitude and intervals and usually lack a stable phase relationship with the QRS complex. The muscle artifact is often more prominent in limb leads (I, II, III, aVR, aVL, aVF), but its severity depends on the localization of muscle activity, electrode placement sites, and the degree of skin-electrode contact, so the artifact may also be prominent in precordial leads (V1–V6) — the distribution across leads is inconsistent and is not in itself a diagnostic sign.
Upon careful analysis beneath the "noise", normal P waves, QRS complexes, and T waves can be distinguished — this is precisely what differentiates the artifact from a true arrhythmia. The ST segment and TP segment are most often affected the most because these are areas with low intrinsic signal amplitude that are easily overlaid by tremor.
In patients with true hypothermia, the shivering artifact may be combined with characteristic ECG changes: sinus bradycardia, prolongation of the PQ (PR) interval, QT interval, QRS complex widening, and an Osborn wave (an additional delayed positive or negative notch/wave in the J-point region, usually most prominent in the inferior and lateral leads). These changes are variable and not mandatory in every patient. It is important not to confuse the Osborn wave with the tremor artifact itself — it is a stable element of the complex repeating from cycle to cycle, rather than chaotic noise.
| Sign | Shivering artifact | True arrhythmia |
|---|---|---|
| Oscillation regularity | irregular, without a stable phase relationship with QRS | organized atrial or ventricular activity with its own structure (e.g., F waves in flutter) |
| Relationship with QRS | not related to heart rhythm | related to rhythm |
| Behavior at rest | decreases/disappears | does not change |
Mechanism
Shivering (tremor) is involuntary rhythmic skeletal muscle contractions, a physiological thermogenesis mechanism during hypothermia. The electromyographic activity of shivering muscles generates its own biopotentials, which can be comparable in amplitude to cardiac signals and are recorded by surface ECG electrodes alongside the true cardiac signal. The electrocardiographer does not differentiate the electrical signal source — it sums the myographic noise from skeletal muscles with the cardiographic signal from the heart. The stronger the muscle contractions, the higher the amplitude and irregularity of the superimposed oscillations. This is purely technical interference unrelated to the electrical activity of the heart itself.
Causes
- Hypothermia (overcooling) of any etiology is the most common cause of pronounced muscle shivering
- Shivering during fever, infectious diseases
- Post-anaesthetic shivering (following general anesthesia)
- Tremor in Parkinson's disease and other extrapyramidal disorders
- Essential tremor, anxiety, fright, marked patient agitation
- Cold room, insufficient covering of the patient during recording
- Muscle tension due to discomfort, pain, uncomfortable position on the couch
Differential diagnosis
- Atrial flutter (coarse-wave form) — repeating organized F waves, usually most prominent in II, III, aVF, with an atrial rate of approximately 240–340/min; conduction to the ventricles may be fixed or variable, unlike chaotic irregular shivering
- Fine-wave ventricular fibrillation — a life-threatening rhythm without discernible QRS complexes; with severe artifact, QRS complexes may be completely masked, so the absence of clear QRS complexes on a single fragment does not rule out VF. If VF is suspected, immediately assess consciousness, breathing, and pulse; in the absence of signs of circulation, initiate the resuscitation protocol and check the rhythm in another lead or on the monitor; traceable true QRS complexes support the diagnosis of artifact, but their absence does not confirm the diagnosis of artifact
- 50 Hz mains interference — strictly regular sinusoidal oscillations of constant frequency and amplitude, unlike irregular tremor
- Motion artifact — associated with large patient shifts or respiration, usually slower and more irregular in shape, whereas tremor yields a more uniform high-frequency ripple
- Osborn wave in true hypothermia — a stable element repeating in every cycle at the J point, rather than chaotic noise
Clinical significance and management
The artifact itself is not dangerous for the patient, but is diagnostically hazardous: it can mask true arrhythmia, hide ST-segment elevation or depression, distort the evaluation of the T wave and QT interval, and in severe cases mimic atrial flutter or ventricular fibrillation, provoking erroneous emergency actions.
The physician should: minimize patient movements, ensure a comfortable position and warming as indicated (eliminate the cause of shivering if possible without compromising emergency care); check the contact tightness and position of the electrodes; repeat the recording; evaluate the rhythm using sections of the trace with the least noise, where P and QRS waves are distinctly visible separately. Sedation to eliminate tremor artifact is not used as a standard technique — it is not a method for correcting hypothermia itself and may impair breathing and thermoregulation; it is considered only for specific clinical indications and under monitoring. If severe hypothermia is suspected, emergency care must not be delayed for the sake of ECG recording quality.
If the artifact is combined with the clinical picture of hypothermia, diagnosis and management are not limited to ECG analysis: body temperature, hemodynamics, consciousness, breathing, and electrolytes are assessed. ECG signs of hypothermia (bradycardia, PQ and QT changes, QRS widening, possible Osborn wave) are variable and not mandatory in every patient, and therefore do not replace clinical evaluation. Treatment is determined by the severity of hypothermia and the patient's condition and includes controlled rewarming and correction of causes and electrolyte disturbances according to clinical protocols.
Common interpretation errors
- Mistaking tremor artifact for atrial flutter or polymorphic ventricular tachycardia and initiating unjustified emergency therapy
- Concluding that QRS complexes are absent on a noisy recording, and consequently that ventricular fibrillation is present, without clinical assessment of the patient (consciousness, breathing, pulse) and without attempting to obtain a cleaner recording fragment
- Failing to attempt to warm and calm the patient before a repeat recording, even though this is the simplest way to reduce interference
- Confusing the Osborn wave (a true complex element in hypothermia) with one of the artifact notches
- Evaluating the ST segment and QT interval on a section with pronounced interference instead of finding a cleaner recording fragment
- Failing to check electrode contact tightness, assuming the problem necessarily lies with the patient rather than the application technique
1. Which sign is most characteristic of the hypothermia shivering artifact?
The tremor artifact produces chaotic interference, irregular in amplitude and intervals, which decreases when the patient's muscles are at rest.
2. Can ventricular fibrillation be ruled out from a single noisy ECG strip in a patient with a tremor artifact?
A severe muscular artifact can completely mask QRS complexes, so the diagnosis of ventricular fibrillation cannot be ruled out based on a single questionable strip — patient assessment and a repeated/cleaner recording are needed.
3. What distinguishes a tremor artifact from an Osborn wave in true hypothermia?
The Osborn wave is a true, reproducible element of the complex at the J point from cycle to cycle, whereas the artifact is random noise not related to the cardiac cycle.
Frequently asked questions
How to distinguish a shivering artifact from atrial flutter?
Atrial flutter demonstrates repeating, organized F waves, usually most prominent in II, III, aVF, with an atrial rate of approximately 240–340/min; the morphology and visibility of the waves may vary, and atrioventricular conduction can be fixed or variable. The tremor artifact is irregular in amplitude and intervals, its frequency and morphology change chaotically from cycle to cycle, and the interference weakens or disappears when the patient's muscles relax.
Is the shivering artifact dangerous on its own?
The signal itself is not dangerous to the patient, but it can lead to diagnostic errors — masking real arrhythmias or ischemic ST-T changes, or mimicking a life-threatening rhythm and triggering unjustified emergency interventions.
What to do if severe shivering interference is visible on the ECG?
Minimize patient movement, ensure a comfortable position and warming if indicated, check electrode contact quality, and repeat the recording. Rhythm and ST-T evaluation should be performed on the least noisy sections of the tracing. If a life-threatening rhythm cannot be reliably ruled out due to interference, first assess the patient's condition (consciousness, breathing, pulse) rather than relying on a single questionable strip of the recording.
Is this artifact necessarily associated with true hypothermia?
No, similar interference occurs with any tremor — chills associated with fever, post-anesthetic shivering, anxiety, Parkinson's disease, and even simply in a cold room. True hypothermia may additionally be accompanied by bradycardia, PQ and QT prolongation, QRS widening, and an Osborn wave, but the severity and combination of these signs are variable and are evaluated along with temperature measurement and the clinical picture.
How to distinguish a tremor artifact from an Osborn wave?
The Osborn wave is a stable additional element at the J point that repeats identically in each complex. The tremor artifact consists of chaotic, irregular oscillations not strictly bound to the structure of each individual complex.
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Related terms
More in the section «Artifacts and Placement Errors»
Sources
- Goldberger A.L. Clinical Electrocardiography: A Simplified Approach
- Hampton J.R. The ECG Made Easy
- AHA/ACCF/HRS Recommendations for Standardization of ECG, 2009
- Orlov V.N. Guide to Electrocardiography
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.