TIMI frame count is an alternative to the TIMI flow. Unlike TIMI flow, it offers a quantitative assessment of coronary artery blood flow. TIMI frame count is expressed as the number of frames required for dye to reach a standardized distal landmark in a coronary artery.

The first frame is counted when the dye touches both border of the coronary artery and moves forward with at least 70% opacification of the vessel lumen.
The last frame is counted when the dye enters the standardized distal landmark:

• Right coronary artery: first branch of the posterolateral artery
• Circumflex artery: most distal branch of the obtuse marginal branch
• Left anterior descending artery (LAD): distal bifurcation of LAD

Correction factor is used for the left anterior descending artery (LAD) - the number of frames is divided by 1.7 to compensate for its longer length compared to the circumflex and the right coronary arteries.

For a frame rate of 30 frames per second, a normal TIMI frame count is 21±3. But:

• increased or decreased flow rate of dye injection may change TIMI frame count by ≤2 frames
• injection during diastole reduces TIMI frame count by 6 frames
• nitrates may increase TIMI frame count by 6 frames