ECG criteria
- Rhythm: sinus, often with tachycardia; atrial fibrillation or flutter occurs in a subset of patients, more commonly with pronounced atrial dilation and advanced HFrEF
- Intraventricular conduction: complete left bundle branch block (QRS ≥120 ms, broad notched R in I, aVL, V5–V6, absence of Q in these leads) is frequently seen in a subset of DCM patients; non-specific intraventricular conduction delay, RBBB, or normal conduction are also possible
- QRS voltage: may be low (<5 mm in limb leads, <10 mm in precordial leads) — prompting a search for contributing causes (pericardial effusion, obesity, COPD, infiltrative diseases), or increased in the presence of concurrent hypertrophy
- Q wave: pathological Q waves without a history of myocardial infarction (pseudoinfarct pattern) in the inferior or anterior leads is a non-specific sign; the etiology should be clarified clinically and via imaging methods
- ST segment and T wave: non-specific diffuse ST-T changes, flattened or inverted T waves in multiple lead groups
- Atrial enlargement: signs of left atrial enlargement (P mitrale) in secondary mitral regurgitation
- QT interval: with a wide QRS complex (e.g., LBBB), the measured QTc is increased due to QRS widening rather than necessarily true prolongation of repolarization; to assess true repolarization, the JT/JTc interval or QRS-adjusted QT correction formulas should be used
- Ectopic activity: frequent ventricular extrasystoles, runs of ventricular tachycardia on Holter monitoring
What it looks like on ECG
The ECG in DCM is non-specific with no pathognomonic criteria, and in a portion of patients the tracing remains nearly normal despite overt clinical heart failure — the diagnosis is established by echocardiography and refined by cardiac MRI, with the ECG serving merely as a supportive modality.
One of the frequent and clinically significant findings is left bundle branch block (QRS ≥120 ms, broad notched or slurred R wave in I, aVL, V5–V6, discordant negative T wave in the same leads, absence of normal Q in V5–V6). LBBB is important for cardiac resynchronization therapy indications, but it is not present in all patients: the ECG may demonstrate a non-specific intraventricular conduction delay, right bundle branch block, fascicular block, or be essentially normal.
Sinus tachycardia is frequently registered as a compensatory response to reduced cardiac output, or atrial fibrillation in a subset of patients secondary to left atrial enlargement and elevated filling pressures.
QRS voltage may be reduced — a non-specific finding that requires ruling out secondary causes (accompanying pericardial effusion, obesity, COPD, infiltrative diseases, technical factors) rather than being directly interpreted as a measure of fibrosis. Q waves unrelated to a coronary event (pseudoinfarct Q waves) may appear in the inferior or anteroseptal leads — this pattern is non-specific and may be related to either focal fibrosis or altered geometry and electrical activation of the dilated ventricle; the ECG cannot differentiate it from an ischemic scar, and the etiology is clarified via clinical evaluation, coronary angiography, and contrast-enhanced MRI.
| Element | Typical finding |
|---|---|
| Rhythm | sinus tachycardia, AF in a subset of patients |
| QRS | LBBB in some patients, occasionally low voltage |
| ST-T | diffuse non-specific changes |
| Q | pseudoinfarct Q waves possible with no history of MI |
| Atria | P mitrale (LA enlargement) |
Holter monitoring frequently reveals ventricular ectopy and nonsustained ventricular tachycardia, which helps assess the risk of sudden death alongside other criteria.
Mechanism
DCM is fundamentally driven by cardiomyocyte injury and death replaced by interstitial and focal fibrosis, leading to dilation of the left (or rarely both) ventricular cavity and a reduced ejection fraction. The distribution of fibrosis is heterogeneous: remodeling, dilation, fibrosis itself, and conduction system involvement can lead to left bundle branch block, non-specific intraventricular conduction delay, or other conduction abnormalities, while also creating a substrate for re-entry ventricular arrhythmias — though there is no direct obligatory causal link between fibrosis and a specific type of block. Ventricular wall stretching and elevated chamber pressures lead to atrial dilation, promoting atrial fibrillation. The diffuse and variable nature of myocardial involvement explains the non-specificity and heterogeneity of ST-T and QRS changes on the ECG; moreover, the ECG patterns of DCM and ischemic cardiomyopathy can overlap, and the localization of ST-T changes and Q waves does not reliably determine etiology.
Causes
- Idiopathic (up to half of cases, some genetically determined with mutations in titin, lamin A/C, and other cytoskeletal and nuclear envelope proteins)
- Familial/inherited DCM
- Myocarditis (viral, including sequelae of acute myocarditis)
- Toxic: alcoholic cardiomyopathy, chemotherapy cardiotoxicity (anthracyclines, trastuzumab)
- Tachycardia-induced cardiomyopathy (prolonged uncontrolled tachyarrhythmia)
- Peripartum cardiomyopathy
- Endocrine and metabolic causes (hypothyroidism, thiamine deficiency)
- Infiltrative and systemic diseases (cardiac sarcoidosis, Chagas disease)
- Muscular dystrophies (Duchenne, Becker) with cardiac involvement
Differential diagnosis
- Ischemic cardiomyopathy (multivessel coronary artery disease sufficient to account for the dysfunction) — by modern definition a distinct etiologic category, separate from non-ischemic DCM; it can present with a similar phenotype of dilation and diffuse systolic impairment. Regional wall motion abnormalities on echocardiography are not specific to coronary artery disease and also occur in myocarditis, sarcoidosis, and genetic forms of DCM, whereas global impairment is also possible in ischemic cardiomyopathy — regionality/diffuseness per se is not used as a sole criterion. The probability of coronary artery disease is assessed clinically, via coronary anatomy or functional ischemia tests, and by late gadolinium enhancement patterns on MRI: an ischemic scar is typically subendocardial or transmural within a vascular territory.
- Hypertrophic cardiomyopathy in the dilated phase — high QRS voltage and deep Q waves in the lateral and inferior leads at earlier stages, unlike the predominantly low voltage seen in pure DCM.
- Myocarditis — acute onset, often with ST-elevation or PR depression; normalization of LV function is possible; upon chronification, the clinical and ECG picture merges with DCM.
- Tachycardia-induced cardiomyopathy — reversible after arrhythmia elimination (rate control in AF, ablation); it is crucial not to miss this potentially reversible variant.
- Arrhythmogenic right ventricular cardiomyopathy — predominant right ventricular involvement; ECG features are non-specific and evaluated as part of a diagnostic criteria set, unlike left ventricular dilation in classic DCM.
Clinical significance and management
DCM is a major cause of heart failure with reduced ejection fraction. With the development of refractory end-stage heart failure, the patient may be evaluated for heart transplantation or mechanical circulatory support. Risks: progressive heart failure, thromboembolism from dilated chambers, ventricular tachyarrhythmias, and sudden cardiac death.
Electrocardiography is part of the initial workup for suspected DCM, but the diagnosis is established by clinical data and imaging — typically echocardiography (dilation and reduced left ventricular ejection fraction not explained by abnormal loading conditions or sufficient coronary artery disease); contrast-enhanced cardiac MRI is recommended to clarify etiology, characterize myocardial tissue fibrosis, and differentiate from myocarditis and infiltrative processes, especially when echocardiography is inconclusive.
Practical tasks for a physician when analyzing an ECG: record the width and morphology of the QRS complex. The presence of LBBB with QRS ≥150 ms in patients with persistent symptomatic heart failure with reduced ejection fraction despite optimal medical therapy and an ejection fraction ≤35% is the most compelling indication to consider cardiac resynchronization therapy; for QRS 130–149 ms, the decision is made individually taking into account QRS morphology, rhythm (sinus/AF), and functional class, whereas with QRS <130 ms CRT is usually not indicated. Next, evaluate the rhythm (rate or rhythm control in AF), look for signs of ventricular ectopy; Holter monitoring can detect arrhythmias and complement the assessment of sudden death risk, but the mere presence of SVT or frequent VES does not usually dictate implantable cardioverter-defibrillator implantation.
For primary prevention of sudden death, the decision regarding an ICD is generally considered when left ventricular ejection fraction remains ≤35% after at least approximately 3 months of optimal therapy, with symptomatic heart failure and a life expectancy of more than one year; in genetic DCM (e.g., with an LMNA mutation), pronounced late gadolinium enhancement on MRI, unexplained syncope, sustained or inducible ventricular tachycardia, ICD indications may arise even with an ejection fraction above 35%. For secondary prevention, a history of cardiac arrest or hemodynamically significant ventricular tachycardia takes priority over other criteria. A separate task is to exclude reversible causes (tachyarrhythmia, toxic exposures, endocrine disorders) — this takes precedence over establishing a definitive diagnosis of idiopathic DCM.
Common interpretation errors
- Interpreting pseudo-infarction Q waves as a sign of a prior myocardial infarction without clinical and anamnestically confirmed coronary events.
- Ignoring LBBB as an "incidental finding" without assessing its significance for cardiac resynchronization therapy indications.
- Diagnosing DCM based solely on ECG — this is a diagnosis that requires imaging (echocardiography, MRI when necessary) and the exclusion of secondary causes, including coronary artery disease sufficient to explain the dysfunction.
- Failing to account for the tachy-induced component in newly diagnosed AF with dilatation and reduced ejection fraction — missing a potentially reversible cause.
- Automatically interpreting a prolonged measured QT interval in the presence of a wide QRS as true repolarization prolongation without accounting for the contribution of complex widening.
1. Which statement about left bundle branch block in DCM is correct?
LBBB is frequently found in DCM due to remodeling and conduction disturbances, but there is no specific ECG criterion for DCM, and the ECG may be nearly normal.
2. What is the primary method for establishing the diagnosis of dilated cardiomyopathy?
The diagnosis of DCM is based on clinical data and imaging — usually echocardiography (dilatation and reduced left ventricular ejection fraction); the ECG merely complements the picture.
3. Which type of cardiomyopathy is potentially reversible after eliminating the cause?
With prolonged uncontrolled tachyarrhythmia, left ventricular function may significantly recover after rate or rhythm control.
Frequently asked questions
Can DCM be diagnosed by ECG alone?
No. The ECG in DCM is nonspecific and can be nearly normal. The diagnosis is established based on clinical data and imaging, usually echocardiography (dilation and reduced left ventricular ejection fraction), with the exclusion of abnormal loading conditions or coronary artery disease sufficient to explain the dysfunction. Cardiac MRI is recommended to clarify etiology and tissue characterization, especially if echocardiography is inconclusive.
Why is left bundle branch block frequently found in DCM?
Remodeling, dilation, fibrosis, and involvement of the left ventricular conduction system can impair uniform impulse propagation and lead to left bundle branch block, although there is no direct obligatory causal link. LBBB is one of the frequent and clinically significant findings in DCM (occurring in a significant proportion of patients, with the exact percentage depending on the cohort), but it is not a specific or mandatory sign; it is important for selecting cardiac resynchronization therapy.
Is dilated cardiomyopathy dangerous?
Yes, it leads to progressive heart failure, increases the risk of thromboembolism from dilated chambers, and ventricular tachyarrhythmias up to sudden cardiac death. The prognosis depends on the etiology, ejection fraction, and response to therapy.
How to differentiate DCM from ischemic cardiomyopathy on ECG?
They cannot be reliably differentiated by ECG: both conditions can present with pathological Q waves and diffuse ST-T changes, and regional versus diffuse reduction in contractility on echocardiography is not a reliable criterion. Ischemic etiology is assessed clinically and using an appropriate anatomical or functional coronary imaging study (coronary angiography or CT coronary angiography as indicated); cardiac MRI with late gadolinium enhancement patterns helps differentiate an ischemic scar (subendocardial or transmural, within a vascular territory) from non-ischemic myocardial injury.
Can DCM be reversible?
Yes, in tachycardia-induced cardiomyopathy, alcoholic cardiomyopathy, and certain toxic forms, left ventricular function can significantly recover after the underlying cause is removed (arrhythmia control, alcohol cessation, discontinuation of cardiotoxic therapy).
ECG Course
Interpretation from basics to myocardial infarction — learn to read any ECG using a systematic algorithm.
- Video lessons and theory for every topic
- Simulator case studies under every lesson
- Unlimited ECG simulator practice
- Study guide: "All ECGs in 25 minutes"
ECG Strip Simulator
ECG, radiology, histology, pathomorphology, pharmacology — thousands of flashcards with detailed explanations.
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Related terms
More in the «Channelopathies and Cardiomyopathies» section
Sources
- Hampton J. The ECG in Practice, 6th ed.
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice, 6th ed.
- Orlov V.N. Guide to Electrocardiography
- Clinical Guidelines of the Russian Ministry of Health on Chronic Heart Failure
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.