What is high lateral thinning in the context of cardiac evaluation?

High Lateral Thinning in Cardiac Evaluation

High lateral thinning refers to reduced myocardial wall thickness (typically ≤5.5 mm end-diastolic thickness) in the lateral wall of the left ventricle, which can represent either chronic transmural myocardial infarction with scar tissue or, less commonly, viable myocardium with limited scar burden that may improve with revascularization. 1

Definition and Anatomic Location

• High lateral thinning specifically involves the lateral free wall of the left ventricle, including regions visualized in leads V5-V6, I, and aVL on ECG, and corresponds to the lateral wall segments on echocardiography and cardiac MRI 2
• Wall thickness ≤5.5 mm measured at end-diastole is the standard threshold for defining regional wall thinning 1
• The lateral wall is particularly important because it is a common site for myocardial fibrosis and late gadolinium enhancement in cardiomyopathies 2

Clinical Significance and Differential Diagnosis

The presence of lateral wall thinning should prompt immediate investigation for underlying structural heart disease, as it may indicate:

• Chronic ischemic cardiomyopathy with prior myocardial infarction in the left circumflex or diagonal artery territory 1
• Hypertrophic cardiomyopathy in the end-stage phase with progressive wall thinning and cavity dilatation—this occurs in approximately 9% of HCM patients who develop systolic dysfunction 3
• Left-dominant arrhythmogenic cardiomyopathy where subepicardial LV lateral wall involvement with fatty infiltration results in myocardial wall thinning 2
• Dilated cardiomyopathy with global or regional wall thinning 4, 3

Diagnostic Evaluation

Echocardiographic assessment should include:

• Measurement of end-diastolic wall thickness in all LV segments using 2D short-axis views from base to apex 2
• Assessment of systolic thickening—normal myocardium should demonstrate 30-50% systolic thickening, while thinned regions with transmural scar show minimal or no thickening 4, 5
• Evaluation for regional wall motion abnormalities (hypokinesis, akinesis, or dyskinesis) 2

Cardiac MRI with gadolinium is essential when lateral thinning is detected because:

• It provides superior assessment of the lateral free wall compared to echocardiography 2
• Late gadolinium enhancement quantifies scar burden—this is critical because 18% of thinned regions have limited scar burden (≤50%) and may improve with revascularization 1
• The pattern of LGE helps differentiate etiologies: subepicardial distribution favors arrhythmogenic cardiomyopathy, while subendocardial or transmural patterns suggest ischemic disease 2, 1
• Wall thickness in thinned regions with limited scar can increase from 4.4 mm to 7.5 mm after revascularization, with resolution of thinning 1

Prognostic Implications

Lateral wall thinning carries important prognostic significance:

• In HCM patients, progressive wall thinning (≥5 mm decrease) occurs in 62% of those who develop systolic dysfunction (ejection fraction <50%), compared to only 4% of those maintaining normal function 3
• Scar extent within thinned regions inversely correlates with both regional (r = -0.72) and global (r = -0.53) contractile improvement after revascularization 1
• Lateral or inferolateral T-wave inversion on ECG in the presence of lateral wall thinning strongly suggests underlying cardiomyopathy and requires comprehensive investigation including cardiac MRI 2

Management Approach

When lateral wall thinning is identified:

• Perform cardiac MRI with gadolinium to quantify scar burden and assess viability 2, 1
• If scar burden is limited (≤50% of thinned region) and coronary disease is present, consider revascularization as contractile function may improve and wall thickness may normalize 1
• If extensive scar (>72% of thinned region) is present, functional improvement is unlikely regardless of revascularization 1
• Serial cardiac imaging is necessary even when initial evaluation shows only thinning without other abnormalities, as this may represent early phenotypic expression of evolving cardiomyopathy 2, 3
• Risk stratification for sudden cardiac death should be performed, particularly if associated with HCM or arrhythmogenic cardiomyopathy 2

Common Pitfalls

• Do not assume all lateral wall thinning represents irreversible transmural scar—nearly one-fifth of thinned regions have limited scar and potential for recovery 1
• Do not rely solely on echocardiography for assessing the lateral wall, as cardiac MRI provides superior visualization of this region 2
• Do not dismiss isolated lateral wall thinning even with normal ejection fraction, as it may represent early or evolving cardiomyopathy requiring longitudinal follow-up 2, 3