M-Mode Waves Simplified

M-Mode Echocardiography: Normal Values and Key Diagnostic Findings

What is M-Mode in Echocardiography?

M-Mode (Motion mode) is a one-dimensional echocardiographic technique that records the motion of cardiac structures along a single ultrasound line over time. It provides:

Excellent temporal resolution

Precise linear measurements

Accurate assessment of valve motion

LV dimension and wall thickness quantification

Although 2D and Doppler imaging are routine, M-mode remains essential for standard chamber measurements and subtle motion abnormalities.

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Standard M-Mode Views

1. Parasternal Long Axis (PLAX) – LV Measurements

Cursor placed perpendicular to LV long axis at the level of mitral leaflet tips.

Measurements Taken:

IVSd (Interventricular septal thickness in diastole)

LVIDd (LV internal diameter in diastole)

LVIDs (LV internal diameter in systole)

LVPWd (Posterior wall thickness in diastole)

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Normal Adult LV M-Mode Values (ASE-Based)

LV Dimensions

LVIDd

Men: 4.2 – 5.8 cm

Women: 3.8 – 5.2 cm

LVIDs

Men: 2.5 – 4.0 cm

Women: 2.2 – 3.5 cm

Wall Thickness

IVSd: 0.6 – 1.0 cm

LVPWd: 0.6 – 1.0 cm

LV Systolic Function

Fractional Shortening (FS): 25 – 45%

Formula:

FS = (LVIDd − LVIDs) / LVIDd × 100

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Aortic Root & Left Atrium (PLAX M-Mode)

Normal Values:

Aortic root: 2.0 – 3.7 cm

Left atrial diameter:

Men: ≤ 4.0 cm

Women: ≤ 3.8 cm

LA/Ao ratio in children: < 1.3

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Mitral Valve M-Mode

Normal Pattern

M-shaped anterior leaflet

E wave > A wave

E-F slope normal

Key Abnormal Findings

1. Reduced E-F slope → Mitral stenosis

2. Increased EPSS (>7 mm) → LV systolic dysfunction

3. Anterior leaflet doming → Rheumatic MS

4. Diastolic fluttering → Aortic regurgitation

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Aortic Valve M-Mode

Normal

Box-like opening pattern

Symmetrical cusp separation

Abnormal

Reduced separation → Aortic stenosis

Eccentric closure line → Bicuspid valve

Fine oscillations → Vegetation

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Common Pathological Patterns on LV M-Mode

1. Concentric LVH

Increased IVSd and LVPWd

Normal or reduced cavity size

Causes: Hypertension, Aortic stenosis

2. Dilated Cardiomyopathy

Increased LVIDd and LVIDs

Reduced fractional shortening

3. Asymmetric Septal Hypertrophy

IVSd > LVPWd (ratio > 1.3)

Suggestive of HCM

4. Paradoxical Septal Motion

Seen in:

LBBB

RV pacing

Post cardiac surgery

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Right Ventricular Assessment (Subtle Role of M-Mode)

TAPSE (Tricuspid Annular Plane Systolic Excursion)

Measured using M-mode in apical 4-chamber view.

Normal: ≥ 17 mm

Reduced in RV systolic dysfunction

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Practical Tips for Accurate M-Mode

Always ensure cursor is perpendicular

Measure at end-diastole (R wave)

Avoid oblique cuts

Average over 3 cardiac cycles (5 in AF)

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Clinical Importance of M-Mode in Modern Practice

Despite advanced imaging techniques, M-mode remains valuable because of:

Superior temporal resolution

Reproducible LV measurements

Quick bedside assessment

Essential component of ASE chamber quantification guidelines

M-mode is simple, fast, and highly informative when used correctly.