ECG criteria
- Low QRS voltage: QRS complex amplitude <5 mm in all limb leads and/or <10 mm in all precordial leads (2009 AHA/ACCF/HRS criteria)
- Voltage-myocardial mass discordance: low or normal QRS voltage with marked LV wall thickening on echocardiography — a key sign of amyloidosis
- Pseudoinfarct Q waves in leads V1–V3 or inferior leads without a convincing history of infarction
- The QRS axis may be normal, leftward, or rightward deviated; marked axis deviation is neither an obligatory nor a specific sign
- Conduction disorders: first-degree AV block, bundle branch block, complete AV block as infiltration spreads
- Atrial fibrillation or atrial flutter, frequently recurrent
- Nonspecific ST-T changes, flattened or inverted T wave in multiple leads
- In some cases, nonspecific QTc prolongation is possible; drug and metabolic causes should be excluded
What it looks like on ECG
A classic, albeit nonspecific, sign is low QRS voltage: QRS complex amplitude <5 mm in all limb leads and/or <10 mm in all precordial leads. Particularly characteristic is the contrast between modest ECG voltage and marked LV wall hypertrophy on echocardiography — this voltage-wall thickness discordance is most typical for cardiac amyloidosis, where the myocardium is infiltrated by amyloid rather than truly hypertrophied. The sign is nonspecific: it is most useful in combination with wall thickening when amyloidosis (especially AL type) is suspected, but is not obligatory or typical for restrictive cardiomyopathy as a whole — it is absent in a significant portion of patients, including those with transthyretin (ATTR) amyloidosis, and is frequently normal in its other forms.
In precordial leads V1–V3, less commonly in inferior leads II, III, aVF, pathologic Q waves may appear, mimicking a prior myocardial infarction (pseudoinfarct pattern) — a consequence of septal infiltration and impaired excitation propagation rather than necrosis.
The electrical axis of the heart in amyloidosis can be normal, leftward, or rightward deviated; marked axis deviation is not an obligatory sign and has no diagnostic significance on its own. The PQ (PR) interval may be prolonged, first-degree AV block is typical, and with progressive infiltration — high-grade AV block and complete AV block up to the need for pacing. Atrial fibrillation is frequently registered, which may recur and respond poorly to antiarrhythmic therapy due to atrial myocardial infiltration, but this does not preclude cardioversion if standard safety measures are observed (anticoagulation, thrombus evaluation).
The T wave is frequently flattened or inverted in multiple leads, and the ST segment shows no consistent ischemic-type elevation or depression. In other forms of restrictive cardiomyopathy (endomyocardial fibrosis, sarcoidosis, hemochromatosis), QRS voltage may be normal — low voltage is most specific for amyloidosis specifically, but even there it is absent in some patients.
Mechanism
In amyloidosis, extracellular amyloid fibril deposits accumulate between cardiomyocytes, increasing wall thickness on imaging. Amyloid infiltration, concomitant fibrosis, and impaired myocardial electrical homogeneity disrupt excitation propagation and can reduce the recorded total QRS amplitude — this is how low voltage arises despite wall thickening; the mechanism of low voltage is multifactorial and not reducible to a single cause. Infiltration of the conduction system (AV node, bundle of His, and its branches) leads to progressive AV conduction abnormalities. Atrial myocardial involvement creates a substrate for atrial fibrillation. In non-amyloid forms of restriction (fibrosis, sarcoid granulomas), electrical changes depend on the location and extent of the lesion and are less predictable.
Causes
- Cardiac amyloidosis (AL amyloidosis, transthyretin amyloidosis — hereditary and age-related/wild-type)
- Endomyocardial fibrosis
- Hypereosinophilic syndrome (Löffler endocarditis)
- Cardiac sarcoidosis — rarely forms a classic restrictive phenotype; usually classified as an infiltrative/granulomatous cardiomyopathy with a predominantly arrhythmogenic, sometimes dilated course
- Hemochromatosis (may transition to a dilated phenotype at a late stage)
- Radiation heart disease
- Scleroderma and other systemic connective tissue diseases
- Idiopathic restrictive cardiomyopathy
Differential diagnosis
- Constrictive pericarditis: similar filling hemodynamics; ECG is nonspecific (atrial fibrillation, nonspecific ST-T changes are possible), low voltage is possible, especially with concomitant effusion, but is not solely a consequence of pericardial thickening; differentiated clinically and by imaging modalities (CT, MRI, catheterization) rather than by ECG
- Hypertrophic cardiomyopathy: ECG typically shows high QRS voltage and signs of LV hypertrophy rather than low voltage — the opposite picture
- True prior myocardial infarction: pseudoinfarct Q waves in amyloidosis are not accompanied by typical infarction stage dynamics and reciprocal changes; history and imaging are required
- Pericardial effusion and tamponade: also present with low voltage and may be combined with electrical alternans — clarified via echocardiography
- Hypothyroidism: low QRS voltage and bradycardia, but without pseudoinfarct Q waves and marked myocardial mass discordance
Clinical significance and management
ECG signs of restrictive cardiomyopathy are nonspecific individually, but the combination of low QRS voltage with marked wall hypertrophy on echocardiography in a patient with heart failure symptoms and a preserved ejection fraction should direct the diagnostic workup toward cardiac amyloidosis. The physician should order advanced imaging: echocardiography with speckle-tracking strain (apical sparing pattern), and cardiac MRI with contrast. When amyloidosis is suspected, bone scintigraphy with a cardiac tracer (technetium pyrophosphate) is performed simultaneously with a complete workup for monoclonal gammopathy — serum and urine immunofixation and free light chain assay. The diagnosis of ATTR amyloidosis without biopsy is possible only with typical uptake (grade 2–3) on scintigraphy and a negative monoclonal protein test; if a monoclonal protein is detected, a biopsy with amyloid typing is required. Progressive AV block and atrial fibrillation require rate control and, when indicated, pacemaker implantation. In AF or atrial flutter in a patient with cardiac amyloidosis, anticoagulation is generally indicated regardless of the CHA₂DS₂-VASc score because the risk of intracardiac thrombosis is increased; this risk is considered prior to cardioversion, and transesophageal echocardiography is evaluated. Sudden cardiac death is possible with marked conduction system involvement and ventricular arrhythmias against the background of myocardial infiltration.
Common interpretation errors
- Interpreting pseudoinfarct Q waves as a sign of prior infarction without considering the clinical picture and imaging
- Ignoring the discordance between low QRS voltage and marked hypertrophy on echocardiography — a key diagnostic clue
- Attributing low voltage solely to obesity or COPD without analyzing the context
- Overlooking signs of first-degree AV block as "unimportant" in a patient suspected of having an infiltrative disease
- Refusing cardioversion for AF due to expected refractoriness without assessing real indications, anticoagulation, and thromboembolism risk
1. Which ECG sign is most characteristic of cardiac amyloidosis among restrictive cardiomyopathies?
The discordance between low electrical voltage and marked wall thickening on imaging is a key clue to myocardial amyloid infiltration, although the sign is nonspecific.
2. What explains the appearance of pseudoinfarct Q waves in cardiac amyloidosis?
Amyloid infiltration disrupts normal septal depolarization, creating pathological Q waves without true necrosis.
3. What rhythm or conduction disturbance typically progresses in infiltrative restrictive cardiomyopathy?
Infiltration of the conduction system and atrial myocardium leads to progressive AV blocks and recurrent atrial fibrillation.
Frequently asked questions
Which ECG sign is most characteristic of cardiac amyloidosis?
Low QRS voltage combined with marked left ventricular wall thickening on echocardiography—the so-called voltage-mass mismatch. This combination distinguishes amyloidosis from true hypertrophy, where QRS voltage is typically increased. The sign is nonspecific and absent in a significant proportion of patients, especially with ATTR amyloidosis.
How does the ECG in restrictive cardiomyopathy differ from constrictive pericarditis?
ECG alone does not always reliably differentiate these conditions; both can present with low voltage and nonspecific ST-T changes. Differential diagnosis is based on echocardiography, cardiac MRI or CT, and invasive hemodynamics, rather than isolated ECG criteria.
Is restrictive cardiomyopathy dangerous in terms of arrhythmias?
Yes, especially in amyloidosis and sarcoidosis: infiltration of the conduction system leads to progressive AV blocks up to complete heart block, and atrial involvement results in recurrent atrial fibrillation with a high risk of intracardiac thrombus formation and thromboembolism.
Why do pseudoinfarction Q waves occur on the ECG in amyloidosis without a prior myocardial infarction?
Amyloid infiltration of the interventricular septum disrupts normal propagation of excitation, forming pathological Q waves in the chest leads without true myocardial necrosis. History, dynamics, and imaging data help differentiate this from myocardial infarction.
Should amyloidosis always be suspected in the presence of low QRS voltage?
No, low voltage is nonspecific and occurs in obesity, COPD, pericardial effusion, and hypothyroidism. Suspicion of amyloidosis increases when low voltage is combined with thickened LV walls on echocardiography and clinical heart failure.
ECG Course
Interpretation from basics to myocardial infarction — learn to read any ECG using a systematic algorithm.
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Related terms
More in the «Channelopathies and Cardiomyopathies» section
Sources
- Goldberger's Clinical Electrocardiography, 9th ed.
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice, 6th ed.
- AHA/ACCF/HRS Recommendations for the Standardization of the 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.