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← Section V · Cardiac Masses, Pericardial Disease, Contrast and New Applications
V.D

Assessment of Myocardial Perfusion with Contrast

3 cards

Notes

Principle

  • Microbubbles behave as intravascular tracers (do not leave the vascular space).
  • Their presence within the myocardium reflects myocardial capillary blood volume.
  • Real-time imaging tracks contrast wash-in and wash-out.

Flash-replenishment technique

  1. Steady-state contrast infusion.
  2. High mechanical index (MI ~1.0) 'flash' destroys myocardial microbubbles.
  3. Low MI continuous imaging tracks replenishment kinetics.
  4. Replenishment rate (β) reflects capillary flow velocity; plateau intensity (A) reflects capillary blood volume.
  5. Myocardial blood flow (MBF) ∝ A × β.

Ischemia detection

  • Regional delay in replenishment or reduced plateau intensity in a coronary territory → ischemia.
  • Contrast can augment stress echo by defining borders AND perfusion.

Viability assessment

  • Myocardial contrast enhancement in a wall-motion-abnormal region suggests viable microvasculature (potential for functional recovery after revascularization).
  • Absent contrast enhancement in the segment suggests scar (transmural infarction).

Clinical use

  • Not routinely performed outside specialized centers due to technical demand and off-label use of some agents.
  • More often used in research; PET, SPECT, and cMRI are the standard clinical perfusion tools.

Advantages

  • Bedside, portable.
  • No ionizing radiation.
  • Simultaneous assessment of wall motion, chamber size, and perfusion.

Cards

  • basicV.D-001
    Why do microbubbles work as intravascular tracers?
    → They are too large to leave the vascular space and remain confined to the intravascular compartment — so their myocardial concentration reflects capillary blood volume.
  • basicV.D-002
    Describe the 'flash-replenishment' technique for myocardial perfusion echo.
    → During steady-state contrast infusion, a brief high-MI 'flash' pulse destroys myocardial microbubbles. Subsequent low-MI imaging tracks replenishment kinetics: replenishment rate (β) reflects capillary flow velocity; plateau intensity (A) reflects capillary blood volume. MBF ∝ A × β.
  • basicV.D-003
    How does myocardial contrast echo distinguish viable vs infarcted myocardium?
    → Contrast enhancement in a wall-motion-abnormal region indicates intact microvasculature and viable myocardium (potential for functional recovery after revascularization). Absent enhancement suggests scar / transmural infarction.