How Cardiac Scar Manifests in Post-MI Patients with Reduced LVEF
In patients with prior myocardial infarction and reduced left ventricular ejection fraction, cardiac scar manifests as a critical arrhythmogenic substrate that independently predicts ventricular arrhythmias, sudden cardiac death, and appropriate ICD shocks—with scar burden >5% of left ventricular mass conferring substantially higher risk regardless of ejection fraction. 1
Clinical Manifestations and Arrhythmic Risk
Arrhythmogenic Substrate
- Myocardial scar tissue creates the anatomical foundation for malignant ventricular tachyarrhythmias by forming areas of slow conduction that facilitate reentrant circuits, typically originating from the subendocardial surface adjacent to dense scar 1, 2
- The reentry circuit spans several centimeters in a complex three-dimensional structure involving endocardial, midmyocardial, or epicardial tissue 2
- Scar heterogeneity (the peri-infarct zone with mixed viable and fibrotic tissue) is particularly arrhythmogenic and strongly predicts ventricular tachycardia inducibility 1
Critical Threshold for Risk
- A sharp step-up in arrhythmic events occurs when scar size exceeds 5% of left ventricular mass (HR 5.2,95% CI 2.0-13.3) 1
- Among patients with LVEF >30%, those with significant scarring (>5%) have 6-fold higher risk than those with minimal scarring (HR 6.3,95% CI 1.4-28.0) 1
- Even among patients with LVEF ≤30%, significant scarring confers nearly 4-fold higher risk (HR 3.9,95% CI 1.2-13.1) 1
- Transmural myocardial scar is strongly associated with major arrhythmic events beyond age, sex, cardiovascular risk factors, and resting LVEF (adjusted HR per 10% increase: 1.48,95% CI 1.22-1.80) 3
Diagnostic Detection Methods
Delayed-Enhancement Cardiac MRI (Primary Modality)
- DE-CMR is the preferred non-invasive imaging modality providing high spatial resolution images of scar tissue with 99% sensitivity for acute infarction and 94% for chronic infarction 1, 2
- Demonstrates presence, location, and transmural extent of myocardial scar 1
- Scar detection by DE-CMR is superior to LVEF alone for estimating arrhythmogenic substrate, as extensive scarring may exist with preserved LVEF while severely impaired LV function may show minimal scarring 1
- Infarct surface area and mass identify patients with VT substrate better than LVEF 1, 4
FDG-PET/CT
- Full thickness myocardial scarring shows strong association with major arrhythmic events after accounting for age, sex, cardiovascular risk factors, beta-blocker therapy, and resting LVEF (adjusted HR per 10% increase in scars: 1.48,95% CI 1.22-1.80) 1
CT Imaging
- Wall thinning, hypoperfusion, and delayed enhancement can identify scars 1
- Myocardial scars depicted by CT show good concordance with electrical features from electroanatomic mapping (κ = 0.536) 1
Echocardiography
- Pulse-cancellation echocardiography (eScar technique) can detect scar presence in ≥1 segment, which is associated with appropriate ICD shocks (80% in cases vs 52% in controls, P = 0.004) 5
- Threshold of ≥3 segments by eScar shows AUC of 0.715 for predicting ICD shocks 5
ECG-Based Assessment
- Modified Selvester QRS score correctly diagnoses scar presence with AUC of 0.91 and quantification correlation of r=0.74 in patients with LVEF ≤35% 6
- Each 3-point QRS-score increase (representing 9% LV scarring) associates with OR 2.2 (95% CI 1.5-3.2) for inducing monomorphic VT 6
- Performance remains robust in patients with hypertrophy, conduction defects, and nonischemic cardiomyopathy (AUC 0.81-0.94) 6
Prognostic Implications
Mortality and Adverse Events
- Extent of myocardial scar is associated with increased all-cause mortality independent of LVEF 1
- Extent of peri-infarct zone is a strong independent predictor of all-cause and cardiac mortality even after adjusting for LVEF 1
- Scar index predicts all-cause death or heart transplantation 1
- Presence of regional fibrosis/scar predicts appropriate ICD therapy irrespective of LVEF 1
Ventricular Arrhythmias
- Scar distribution identifies substrate for inducible VT independently of LVEF 1
- Infarct transmurality is a significant predictor of appropriate ICD therapy and death 1
- Total infarct size as percent of LV mass is the only significant independent predictor of spontaneous sustained monomorphic VT (OR 1.33 per% change, 95% CI 1.12-1.6) and VT inducibility (OR 1.3 per% change, 95% CI 1.1-1.6) 7
Scar Location Impact
- Presence of scar in antero-basal left ventricular segments independently predicts worse postoperative outcomes following surgical ventricular reconstruction 8
- Patients with postoperative LV end-systolic volume index >60 ml/m² show higher risk of cardiac events (HR 3.67) 8
Clinical Presentation
Arrhythmic Manifestations
- Typically presents as sustained monomorphic ventricular tachycardia with QRS morphology determined by the exit site where reentry wavefronts propagate from scar 2
- May cause hemodynamic instability, syncope, or electrical storm (recurrent VT/VF with frequent appropriate ICD firing) 2
- Multiple VT morphologies may be induced in the same patient despite monomorphic presentation 2
Quality of Life Impact
- Significantly impairs quality of life, especially when associated with ICD shocks 2
- ICD shocks are associated with higher mortality and impaired quality of life 2, 9
Important Clinical Caveats
Scar vs. Ischemia
- Myocardial scar, not ischemia, is associated with appropriate ICD shocks and sudden cardiac death in stable patients with LVEF ≤35% 3
- Non-transmural scar/hibernation and markers of myocardial ischemia (global or peri-infarct ischemia, coronary flow reserve, myocardial blood flows) are not associated with major arrhythmic events 3
Relationship to ICD Shocks
- Myocardial scarring is a predictor of appropriate ICD therapy and arrhythmic events, not a consequence of ICD shocks 9
- The presence and extent of scarring detected by DE-CMR strongly predicts adverse outcomes regardless of LVEF 9