INTRODUCTION
Syncope, defined as transient loss of consciousness due to global cerebral hypoperfusion with spontaneous and complete recovery, is a common and diagnostically challenging presentation. (1,2) Although reflex syncope usually carries a benign prognosis, structural heart disease substantially alters its implications. (3,4) Dilated cardiomyopathy (DCM) is a high-risk substrate because of myocardial fibrosis, ventricular remodeling, conduction system disease, and autonomic dysfunction, and syncope in DCM is associated with ventricular arrhythmias, sudden cardiac death (SCD), and increased mortality. (5-8)
Two device-based strategies deserve particular emphasis from the outset. Implantable loop recorders (ILRs) provide long-term symptom–rhythm correlation in unexplained syncope; last-generation insertable cardiac monitors establish a diagnosis in approximately 42% of patients and guide cardiac device implantation in 15%, (9-11) and in patients with cardiomyopathies at borderline arrhythmic risk, ILR-guided diagnoses led to implantable cardioverter-defibrillator implantation in 20%. (12) Current European guidelines recommend an ILR in patients with DCM, a left ventricular ejection fraction of 36–50%, and unexplained syncope without other arrhythmic risk factors. (12,13) Cardiac resynchronization therapy (CRT), with or without a defibrillator, is a cornerstone of treatment in DCM with reduced left ventricular ejection fraction and left bundle branch block, because it improves symptoms and survival and addresses both conduction-related and arrhythmic mechanisms of syncope; (14,15) ongoing trials such as BRITISH are comparing a defibrillator strategy with an ILR/CRT-pacemaker strategy in non-ischemic cardiomyopathy. (16) This review summarizes the prevalence, mechanisms, prognostic implications, and management of syncope in DCM, with emphasis on arrhythmic risk stratification.
METHODS
A semi-systematic literature search of PubMed/MEDLINE, Scopus, Ovid, and the Cochrane Library was performed from database inception through March 1, 2026. Search terms combined (“syncope” OR “loss of consciousness” OR “fainting”) with (“dilated cardiomyopathy” OR “nonischemic cardiomyopathy” OR “non-ischemic cardiomyopathy” OR “idiopathic dilated cardiomyopathy” OR “DCM”), and additionally with “ventricular arrhythmia,” “ventricular tachycardia,” “sudden cardiac death,” “implantable cardioverter-defibrillator,” “ICD,” “prognosis,” “mortality,” “conduction disorder,” and “heart failure.” Reference lists of retrieved articles and relevant guidelines were manually screened for additional studies. Recent publications recommended during peer review were additionally included.
Eligible publications were original research articles (prospective and retrospective cohort studies, case-control studies, and clinical trials), systematic reviews and meta-analyses, clinical practice guidelines from major cardiovascular societies, and narrative reviews providing mechanistic or clinical insights, addressing the etiology, prevalence, prognosis, or management of syncope in adults (≥18 years) with DCM. Case reports and case series with fewer than 10 patients, exclusively pediatric studies, non-English articles, conference abstracts, and studies limited to hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, or other specific cardiomyopathies without DCM data were excluded.
Titles and abstracts were screened for relevance, and the full texts of potentially eligible articles were reviewed by the authors. Data were extracted on study design, population characteristics, syncope prevalence, mechanisms, risk factors, mortality, and treatment. Given the heterogeneity of study designs and outcomes, a narrative synthesis was performed rather than a formal meta-analysis.
RESULTS
SEARCH RESULTS
Database searching, supplemented by manual screening of reference lists and by recent publications recommended during peer review, identified the literature included in this synthesis, comprising original cohort studies and clinical trials, systematic reviews and meta-analyses, clinical practice guidelines and consensus documents, and narrative reviews.
PREVALENCE OF SYNCOPE IN DILATED CARDIOMYOPATHY
The prevalence of syncope in DCM depends on the study population and heart failure (HF) severity. In a retrospective analysis of 897 patients with DCM, syncope occurred in 30 (3.3%). (6) Among patients with advanced HF (New York Heart Association [NYHA] class III–IV), prevalence rises to 12–14%; (5,17) Middlekauff et al reported syncope in 12% of 491 patients referred for transplant evaluation. (5) Syncope recurs in approximately 35% of patients after an initial episode, and 29% sustain physical injury. (3,4) In the general population, the incidence of syncope increases sharply after the age of 70 years, reaching 19.5 per 1,000 person-years after 80 years, (4) a pattern likely amplified in DCM by concurrent comorbidities.
Mechanisms of Syncope
CARDIAC CAUSES
Cardiac mechanisms account for 50–60% of syncopal episodes in DCM. (6,8)
Ventricular arrhythmias are the most common identified cause, accounting for approximately 33% of cases. (6,18) Ventricular tachycardia (VT) and ventricular fibrillation (VF) cause abrupt reductions in cardiac output, and the DCM substrate—fibrosis, chamber dilation, and abnormal conduction—predisposes to sustained ventricular arrhythmias. (19,20) Among 14 patients with nonischemic DCM and unexplained syncope who received an implantable cardioverter-defibrillator (ICD), Knight et al observed appropriate ICD therapy in 57% during a mean follow-up of 25 months. (7) Similarly, among 103 patients with nonischemic advanced HF and syncope, ICD therapy improved survival compared with historical medically treated controls. (8)
Conduction disorders account for approximately 23% of cardiac syncope in DCM (6,21) and include complete or high-grade atrioventricular (AV) block, sinus node dysfunction with prolonged pauses, and bundle branch block with intermittent progression to complete heart block. The fibrotic process frequently involves the conduction system, explaining the high incidence of conduction abnormalities in this population. (22)
Low cardiac output may precipitate syncope during exertion or increased demand, when the failing ventricle cannot augment output; in advanced HF, syncope may occur even in the absence of documented arrhythmia. (5)
Other cardiac causes include atrial fibrillation with rapid ventricular response or long pauses, pulmonary embolism, and, rarely, dynamic outflow tract obstruction in specific DCM subtypes. (1,2)
NON-CARDIAC CAUSES
Non-cardiac mechanisms are identified in a substantial minority of patients with DCM and syncope. (6) Neurally mediated (reflex) syncope, including vasovagal syncope, situational syncope, and carotid sinus hypersensitivity, accounts for approximately 7% of cases. (1,2,6,23) Orthostatic hypotension accounts for another 7% (6,24) and results from HF-related autonomic dysfunction, (25) diuretic-induced volume depletion, vasodilator therapy (angiotensin-converting enzyme [ACE] inhibitors, angiotensin receptor blockers [ARBs], and nitrates), a blunted heart rate response under beta-blockade, and age-related impairment of baroreceptor function. (24)
Environmental temperature extremes. Ambient temperature extremes may precipitate or exacerbate syncope and related symptoms in DCM. Heat exposure induces cutaneous vasodilation, sweat-related volume loss, and a fall in central venous pressure and stroke volume, (26) which a failing ventricle with limited preload reserve compensates poorly; these effects are amplified by diuretics, renin–angiotensin system inhibitors, angiotensin receptor–neprilysin inhibitors, sodium–glucose cotransporter 2 inhibitors, and beta-blockers, which limit volume or heart-rate compensation and predispose to orthostatic hypotension. (24,27) In older adults with chronic conditions, heatwaves are associated with increased heat-related hospitalizations, with the risk modified by commonly used medications. (27) Cold exposure, conversely, increases sympathetic tone, afterload, and myocardial oxygen demand and may promote ventricular arrhythmias and HF decompensation. (28) In a multinational analysis of 27 countries, both extreme heat and extreme cold were associated with increased cardiovascular mortality, with the greatest relative excess for heart failure. (29) Direct evidence linking temperature extremes to syncope specifically in patients with DCM, however, remains limited, and these associations are largely extrapolated from broader heart failure and older-adult populations. Patients with DCM should therefore receive individualized advice on heat avoidance and fluid intake, and diuretic and vasodilator doses should be reviewed during heatwaves, taking into account congestion status and renal function.
UNEXPLAINED SYNCOPE
Despite comprehensive evaluation, 30–37% of syncopal episodes remain unexplained. (1,6) In DCM, unexplained syncope carries ominous implications, as occult ventricular arrhythmias are frequently responsible. (7,8,30) Brilakis et al evaluated 30 patients with idiopathic DCM and syncope and found that patients remained at elevated risk, and frequently benefited from ICD implantation, even when the electrophysiological study (EPS) was negative. (30) In the Antiarrhythmics Versus Implantable Defibrillators (AVID) registry, patients with unexplained syncope and inducible ventricular tachyarrhythmias had outcomes similar to those with documented sustained VT. (31)
GENETIC SUBSTRATES
Several pathogenic variants confer disproportionate arrhythmic risk, conduction disease, and syncope, sometimes before severe systolic dysfunction develops. (32) LMNA-related cardiomyopathy is strongly associated with conduction system disease, ventricular tachyarrhythmias, and SCD; (33) truncating FLNC variants are highly arrhythmogenic and frequently associated with myocardial fibrosis; (34,35) and DSP, PLN, RBM20, and DES variants may also increase arrhythmic risk, with phenotypes overlapping arrhythmogenic cardiomyopathy. (36) Unexplained syncope in genetically mediated DCM may therefore reflect advanced electrical instability even without severe ventricular dysfunction.
Genetic testing should be considered in patients with DCM and unexplained syncope, particularly in the presence of (1) a family history of DCM, SCD, or unexplained death before 50 years of age; (2) conduction disease disproportionate to the degree of ventricular dysfunction; (3) disease onset before 50 years of age; (4) skeletal muscle involvement or elevated creatine kinase; or (5) cardiac magnetic resonance (CMR) findings suggestive of a specific genetic etiology (e.g., ring-like or septal mid-wall fibrosis associated with LMNA variants). When pathogenic or likely pathogenic variants in high-risk genes (LMNA, FLNC, PLN, DSP, RBM20) are identified, genotype-specific risk stratification applies, and ICD implantation may be warranted at higher left ventricular ejection fraction (LVEF) thresholds than traditionally recommended, consistent with the 2023 European Society of Cardiology (ESC) guidelines. (22) Cascade genetic screening of first-degree relatives is also recommended. (22,37)
Risk Factors for Syncope in Dilated
Cardiomyopathy
Several expected predictors, including LVEF, (6,38) NYHA class, (6) ischemic versus non-ischemic etiology, (38) atrial fibrillation, and dyslipidemia, (6) have not shown consistent associations with syncope; Abdel-Hadi et al found no significant difference in LVEF between patients with and without syncope. (6) This likely reflects the multifactorial nature of syncope, in which arrhythmogenic substrate, autonomic tone, medication effects, and comorbidities play roles beyond pump function. Myocardial fibrosis detected by late gadolinium enhancement (LGE) on CMR has emerged as a major predictor of ventricular arrhythmias and SCD, with incremental prognostic value beyond LVEF, (39,40) and LMNA, FLNC, DSP, and PLN variants mark heightened arrhythmic risk, particularly when associated with conduction disease, nonsustained VT (NSVT), or unexplained syncope. (22)
Arterial hypertension (61.5% [8/13] vs 23.5% [4/17], P = .08) and diabetes mellitus (46.2% [6/13] vs 5.9% [1/17], P = .03) were more frequent in patients with non-cardiac than with cardiac syncope, (6) suggesting that autonomic neuropathy and orthostatic mechanisms may be particularly important in diabetic patients. (6,25) General predictors of recurrent syncope include structural heart disease, (1,2) impaired renal function, (41) AV block or left bundle branch block, (1) male sex, (4) HF, (1,5) age >70 years, (3,4) and medications predisposing to orthostatic hypotension. (1,24)
Prognostic Impact
Syncope in DCM is a powerful predictor of adverse outcomes, particularly SCD. Annual mortality is 18–33% for cardiac syncope and 0–12% for non-cardiac syncope. (3,5) In 491 patients with advanced HF, syncope predicted sudden death regardless of whether an arrhythmic mechanism was identified, suggesting that all syncope in this population deserves serious attention. (5) In 104 patients with DCM, syncope was an independent predictor of SCD (relative risk 4.7, P < .01). (42) ICD therapy in patients with DCM and syncope was associated with a 2-year survival of 85%, compared with 44% under medical therapy. (8) Grimm et al, studying 343 patients with idiopathic DCM, found that NSVT on Holter monitoring and LVEF <30% predicted arrhythmic events, with syncope adding independent prognostic information. (38)
Several observational studies suggest a survival benefit associated with ICD therapy in selected patients with DCM and syncope. (7,8,13,43,44) In the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), ICD therapy reduced mortality by 23% in patients with NYHA class II–III HF and LVEF ≤35%. (45) Syncope in DCM should therefore be interpreted not merely as a transient symptom but as a potential marker of electrical instability and disease progression.
Management
INITIAL EVALUATION AND RISK STRATIFICATION
Initial evaluation includes detailed history taking, physical examination with orthostatic blood pressure measurement, 12-lead electrocardiogram (ECG), echocardiography, and targeted laboratory testing; (1,2) history alone establishes the diagnosis in up to 50% of cases. (46) High-risk features warranting hospitalization include syncope during exertion or while supine, associated chest pain or dyspnea, preceding palpitations, family history of sudden death before 50 years of age, LVEF <35%, new or significant ECG abnormalities (bifascicular block, corrected QT interval [QTc] >500 ms), significant injury, and known structural heart disease, including DCM. (1,2) The San Francisco Syncope Rule, the Osservatorio Epidemiologico sulla Sincope nel Lazio (OESIL) score, and the Evaluation of Guidelines in Syncope Study (EGSYS) score have been validated for risk stratification, although their performance in DCM requires further study. (1,47)
ADVANCED EVALUATION
Rhythm monitoring. In-hospital telemetry is indicated for high-risk patients. (1,2) After discharge, options include Holter monitoring (24–72 hours) when syncope is frequent, (2) external event recorders (2–4 weeks) for less frequent symptoms, and implantable loop recorders for infrequent, unexplained, recurrent syncope, with a diagnostic yield of 35–43% over 1–2 years. (9,10) Last-generation insertable cardiac monitors offer a comparable diagnostic yield (42%) with a lower clinical workload, (11) and in cardiomyopathy patients at borderline arrhythmic risk at least one ILR-guided diagnosis was made in 44% during a mean follow-up of 19 months, most frequently de novo atrial fibrillation. (12) In DCM, an ILR is particularly useful when LVEF is only mildly or moderately reduced and the arrhythmic origin of syncope remains uncertain. (12,13)
Electrophysiological study. Programmed ventricular stimulation can identify inducible VT, (30,48,49) but its predictive value differs by etiology: sensitivity for subsequent arrhythmic events is approximately 50–80% in ischemic cardiomyopathy (48) but only 20–30% in non-ischemic DCM, so a negative study does not reliably exclude arrhythmic risk. (30,49) Indications for EPS in patients with syncope and structural heart disease, including DCM, have been summarized in dedicated recommendations. (50)
Cardiac magnetic resonance. Beyond assessment of ventricular size and function, CMR enables tissue characterization through LGE, which reflects myocardial fibrosis and arrhythmogenic substrate. (39) LGE independently predicts ventricular arrhythmias, SCD, appropriate ICD therapies, and all-cause mortality in DCM, (40) and its prognostic value extends beyond severely reduced LVEF. (51,52)
Tilt-table testing and carotid sinus massage. Tilt testing is indicated when reflex syncope is suspected and has approximately 90% specificity but variable sensitivity (30–70%), depending on the protocol. (1,2,53) Carotid sinus massage is recommended in patients >40 years of age with unexplained syncope; carotid sinus hypersensitivity is diagnosed when massage produces asystole >3 seconds or a systolic blood pressure decrease >50 mmHg. (1,2)
THERAPEUTIC INTERVENTIONS
Device therapy. ICD implantation is indicated in patients with DCM and syncope with LVEF ≤35% after at least 3 months of guideline-directed medical therapy (GDMT) (class I, primary prevention), documented or inducible sustained VT/VF (class I, secondary prevention), or unexplained syncope with high suspicion of arrhythmic etiology. (44,45,54) In the Defibrillators in Non-Ischemic Cardiomyopathy Treatment Evaluation (DEFINITE) trial, ICD therapy showed a trend toward reduced mortality (hazard ratio 0.65, P = .08) and significantly reduced sudden death. (55) Pacemaker implantation is indicated for documented bradyarrhythmias or conduction system disease, (21,56) and cardiac resynchronization therapy with a defibrillator (CRT-D) is preferred when indications for both CRT and an ICD exist. (14,54) CRT is recommended in symptomatic patients with LVEF ≤35% and left bundle branch block with QRS duration ≥150 ms despite optimal medical therapy, and should be considered at QRS durations of 130–149 ms; (15) the choice between CRT-D and CRT with a pacemaker (CRT-P) may be refined by CMR tissue characterization, genotype, and electrophysiological testing. (16)
Medical therapy. GDMT for HF, including ACE inhibitors, ARBs, or angiotensin receptor–neprilysin inhibitors (ARNIs), beta-blockers, mineralocorticoid receptor antagonists, and sodium–glucose cotransporter 2 (SGLT2) inhibitors, should be optimized. (54,57) Amiodarone or sotalol may be used for VT suppression in selected cases, typically as an adjunct to ICD therapy. (44,58) Medications should be adjusted when orthostatic hypotension is identified, and volume should be repleted when hypovolemia contributes. (24)
Catheter ablation. Ablation is generally considered for recurrent monomorphic VT despite ICD therapy. (44,59,60) Success rates are lower in non-ischemic DCM (approximately 50–70%) than in ischemic cardiomyopathy (approximately 70–80%) because of diffuse, often epicardial or mid-myocardial substrate, and epicardial access is frequently required. (59,60)
Treatment of non-cardiac causes. Vasovagal syncope is managed with education, trigger avoidance, counter-pressure maneuvers, and adequate hydration; (1,23) orthostatic hypotension with medication adjustment, compression stockings, and increased salt and fluid intake. (24) Pacemaker implantation is recommended for recurrent cardioinhibitory carotid sinus hypersensitivity or vasovagal syncope with documented asystole. (1,56)
The main characteristics of syncope in DCM are summarized inTable 1, key practical considerations for its evaluation inTable 2, and a diagnostic and management algorithm is presented inFigure 1.
| Parameter | Findings | References |
|---|---|---|
| Prevalence | 3.3% (general DCM); 12–14% (advanced HF) | (5,6,17) |
| Cardiac causes (total) | 50–60% | (6,8) |
| Ventricular arrhythmias | ≈33% | (6,18) |
| Conduction disorders | ≈23% | (6,21) |
| Low cardiac output | Variable | (5) |
| Non-cardiac causes | ≈14% | (6) |
| Unexplained syncope | 30–37% | (1,6) |
| Recurrence rate | 35% | (3,4) |
| Physical injury rate | 29% | (3,4) |
| Annual mortality (cardiac syncope) | 18–33% | (3,5) |
| Annual mortality (non-cardiac syncope) | 0–12% | (3) |
| Appropriate ICD therapy | 40–60% | (7,8,30) |
| DCM: Dilated cardiomyopathy; HF: Heart failure; ICD: Implantable cardioverter-defibrillator | ||
DISCUSSION
This review shows that syncope affects 3–14% of patients with DCM and carries substantial prognostic weight, with cardiac causes, predominantly ventricular arrhythmias and conduction disorders, responsible for most cases. (5,6,8) Annual mortality differs by as much as 20-fold between cardiac and non-cardiac syncope. (3,5) Even “unexplained” syncope frequently reflects occult arrhythmia, as shown by high rates of appropriate ICD therapy during follow-up, (7,8,30) so the reported 33% contribution of ventricular arrhythmias probably underestimates their true role. Conversely, traditional markers of HF severity such as LVEF and NYHA class do not reliably identify which patients will experience syncope, (6,38) supporting a substrate-oriented model that integrates myocardial fibrosis, arrhythmic burden, conduction disease, autonomic dysfunction, and genotype.
Although 40–60% of patients with DCM and unexplained syncope receive appropriate ICD therapy during follow-up, (7,8,30,43) the Danish Study to Assess the Efficacy of ICDs in Patients with Non-ischemic Systolic Heart Failure on Mortality (DANISH) showed that prophylactic ICD implantation did not significantly reduce all-cause mortality in non-ischemic HF, although SCD was significantly reduced. (61) Decisions should therefore integrate syncope history, fibrosis burden, genetic substrate, and arrhythmic markers rather than LVEF alone. (16) Shared decision-making remains essential, as ICD therapy may be associated with anxiety, psychological distress, and altered quality of life. (62) Contemporary therapies such as ARNIs and SGLT2 inhibitors may both reduce arrhythmogenic substrate and increase orthostatic risk, and their effect on syncope warrants systematic investigation. (63)
Ischemic and non-ischemic DCM differ in arrhythmic substrate, diagnostic yield, and therapeutic outcomes (Table 3). Ischemic cardiomyopathy features re-entry circuits within dense subendocardial scar, whereas non-ischemic DCM is characterized by diffuse mid-myocardial or epicardial fibrosis, (20) lower sensitivity of programmed stimulation, (49) lower ablation success, (59,60) and, in some genetic forms, disproportionate arrhythmic risk. (22)
Future research should develop DCM-specific syncope risk scores integrating clinical, imaging, genetic, and electrophysiological markers; validate wearable monitoring and artificial intelligence–assisted algorithms in diverse DCM populations; clarify the role of catheter ablation through prospective trials; and establish collaborative registries to refine genotype-guided management.
This review has several limitations. The literature on syncope specifically in DCM is sparse and often requires extrapolation from broader populations; studies are heterogeneous, frequently small, and derived from single specialized centers; and much of the evidence predates contemporary HF therapies.
CONCLUSION
Syncope in DCM should be regarded as a major clinical warning sign. Although non-cardiac mechanisms remain possible, structural myocardial disease substantially increases the likelihood of malignant ventricular arrhythmias, conduction abnormalities, and SCD. Contemporary evaluation extends beyond LVEF, integrating prolonged rhythm monitoring, CMR with fibrosis characterization, and genetic testing to identify high-risk phenotypes. A structured, mechanism-oriented approach, with early recognition of high-risk features and timely individualized therapy, including ICD implantation and HF optimization, may improve outcomes in this vulnerable population.