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← Section I · Physical Principles, Instrumentation, Examination Principles
I.K

M-Mode Echocardiography

17 cards

Notes

Basics

  • M-mode = single scan line displayed vs. time.
  • Excellent temporal and axial resolution (sampling > 1000/sec). Better than 2-D for timing.
  • Trade-off: no spatial (lateral) information.

Standard M-mode landmarks (at the mitral valve level, PLAX)

  • E point - maximum anterior excursion of AMVL during early diastolic filling.
  • E-F slope - mid-diastolic closure of the leaflet as filling equalizes.
  • A point - reopening due to atrial contraction.
  • C-D closure line - closed leaflet during systole.

Normal M-mode measurements (PLAX at MV tip level, end-diastole)

  • IVSd < 1.1 cm
  • LVIDd < 5.6 cm (varies with BSA/sex; index for chamber-quant)
  • PWTd < 1.1 cm
  • M-mode dimensions are usually slightly larger than the same 2-D measurement (leading-edge–to–leading-edge).

Normal septal motion

  • IVS normally moves posteriorly (leftward) in early ventricular systole.
  • Peak downward motion of the septum slightly precedes peak upward motion of the posterior wall.

Paradoxical septal motion (M-mode)

  • Early systolic anterior (rightward) motion of the septum. Septal thickening is preserved.
  • Causes: RV volume overload (ASD, severe TR/PR), LBBB or RV pacing, and translational motion after cardiac surgery / AVR.

Classic M-mode findings

  • Acute severe AI - early MV closure (rapid equalization of LV diastolic and aortic diastolic pressures), generous E-point septal separation, soft S1, early diastolic rumble, early AV opening.
  • Severe PAH (pulmonary valve M-mode) - diminutive/absent A-wave, prolonged pre-ejection period, mid-systolic notching ("flying-W sign"), from transient reversal of the PA–RV gradient due to poor PA compliance.
  • Pulmonary stenosis - exaggerated prominent A wave, no mid-systolic notching.
  • Rheumatic MS - reduced E-F slope (most characteristic), thickened leaflets, posterior leaflet moves in the same direction as the anterior (both fixed together), paradoxical anterior septal motion.
  • LA myxoma - mass of echoes behind MV during diastole, echo-free space behind AMVL at diastole onset, delayed appearance of mass into orifice, diminished MV EF slope.
  • Constrictive pericarditis - septal "shudder" or bounce in early diastole, flattening of posterior wall in diastole.
  • Tamponade - RV diastolic collapse (most specific), RA inversion for > 1/3 of the cardiac cycle (more sensitive), plethora of the IVC.
  • Pre-excitation (WPW, left-sided pathway) - inward posterior-wall motion before the IVS.

Aortic root M-mode

  • Aortic root moves anteriorly in systole and posteriorly in diastole (following LA filling/emptying).
  • "Box-like" opening of AV cusps normally opens to ≥ 15 mm.
  • Early systolic closure of AV suggests dynamic LVOT obstruction (HOCM, subaortic membrane).

Cards

  • basicI.K-001
    What is M-mode's main advantage over 2-D echo?
    → Superior temporal and axial resolution (sampling > 1000/sec). Excellent for timing events and measuring rapid motion.
  • basicI.K-002
    On a normal mitral M-mode, what do the E point, E-F slope, A point, and C-D line represent?
    → E point: maximum AMVL excursion during early diastolic filling. E-F slope: mid-diastolic closure. A point: reopening from atrial contraction. C-D line: closed leaflet during systole.
  • basicI.K-003
    State the upper-limit normal M-mode values for IVSd, LVIDd, PWTd.
    → IVSd < 1.1 cm, LVIDd < 5.6 cm (varies with BSA/sex), PWTd < 1.1 cm.
  • basicI.K-004
    How does M-mode measurement of chamber size compare to 2-D?
    → M-mode values are usually slightly larger (leading-edge to leading-edge convention captures more than the 2-D inner-edge measurement).
  • basicI.K-005
    Give three causes of paradoxical septal motion on M-mode.
    → 1) RV volume overload (ASD, severe TR/PR). 2) LBBB or RV pacing. 3) Post-op state (AVR/cardiac surgery — translational motion). Septal thickening is preserved in all.
  • basicI.K-006
    What is the most characteristic M-mode finding in rheumatic mitral stenosis?
    → Reduced E-F slope (loss of the normal 'M' shape of the mitral valve M-mode). Also: thickened leaflets, posterior leaflet moving in the same direction as anterior, paradoxical anterior septal motion.
  • basicI.K-007
    What M-mode findings suggest acute severe aortic insufficiency?
    → Early mitral valve closure (before end-diastole) due to rapid equalization of LV and aortic diastolic pressures, wide E-point septal separation, early AV opening, and often a soft S1.
  • basicI.K-008
    What M-mode findings suggest severe pulmonary hypertension on the pulmonic valve?
    → Diminutive or absent A-wave, prolonged pre-ejection period, and mid-systolic notching ('flying-W sign') due to transient reversal of the PA-to-RV outflow gradient from poor PA compliance.
  • basicI.K-009
    How does the pulmonary valve M-mode differ between pulmonic stenosis and severe pulmonary hypertension?
    → PS: exaggerated prominent A-wave, NO mid-systolic notching. Severe PAH: diminutive/absent A-wave WITH mid-systolic notching.
  • basicI.K-010
    M-mode findings in cardiac tamponade — most sensitive and most specific?
    → Most specific: RV diastolic collapse. Most sensitive: RA inversion > 1/3 of the cardiac cycle (or IVC plethora).
  • basicI.K-011
    What M-mode finding suggests left-sided WPW pre-excitation?
    → Inward (posterior wall) motion BEFORE the interventricular septum, reflecting the accessory pathway pre-exciting the left posterolateral wall.
  • basicI.K-012
    How does an LA myxoma appear on mitral M-mode?
    → Mass of echoes behind the mitral valve during diastole, echo-free space behind AMVL at diastole onset (time-lag before the mass enters the orifice), and diminished MV E-F slope.
  • basicI.K-013
    What M-mode landmarks suggest constrictive pericarditis?
    → Septal 'shudder' or bounce in early diastole (equivalent to the septal bounce and pericardial knock) and flattening of the posterior wall in diastole (completion of most filling in early diastole).
  • basicI.K-014
    What is the sampling rate advantage of M-mode over 2-D echo?
    → M-mode samples > 1000 times per second along a single scan line — providing excellent temporal resolution for measuring rapid events (e.g., valve closure, wall motion timing). 2-D typically 30–100 Hz frame rate.
  • basicI.K-015
    Where in the LV is M-mode typically directed to measure chamber dimensions?
    → At or just apical to the tips of the mitral leaflets, perpendicular to the LV long axis. This is the standard M-mode measurement site for IVSd, LVIDd, PWTd, and LVIDs.
  • basicI.K-016
    Why are M-mode measurements typically larger than 2-D measurements?
    → M-mode uses the 'leading edge to leading edge' convention (echo-tissue interface to echo-tissue interface). 2-D uses inner edge to inner edge (white-black interface). Leading-edge is systematically larger.
  • basicI.K-017
    How does an M-mode of the aortic valve appear when the LV output is severely reduced (low CO)?
    → Reduced amplitude of AV cusp opening (small 'box'), often with early closure due to low forward stroke volume. Contrast with normal cusp separation ≥ 15 mm.