TIMI flow grade
Synonyms and keywords: TIMI flow, TIMI flow grade, TFG

# Overview
The TIMI flow grading system is a widely used method of grading coronary flow.
While the TMPG that was invented by C. Michael Gibson M.S., M.D. assesses  perfusion in the capillary bed at the tissue level, the TIMI flow grade is used to assess epicardial coronary blood flow.

# Clinical Importance and Evaluation
The Thrombolysis In Myocardial Infarction (TIMI) flow grade classification scheme has been widely used to assess coronary blood flow in acute coronary syndromes.  The association of the TIMI Flow Grades (TFG)s with clinical outcomes including mortality has been well documented,       although the association of the TFGs with mortality must be interpreted with caution as there are several confounders:
- The majority of TIMI grade 2 flow is observed in the left anterior descending artery (LAD) territory, whereas the majority of TIMI grade 3 flow is observed in the right coronary artery (RCA).  Thus, the improved mortality observed among patients with TIMI grade 3 flow may be explained at least in part by the fact that inferior myocardial infarction (MI) location is associated with a lower mortality rate. 
- The clinical improvement associated with TIMI grade 3 flow may be nonlinear.  For example, greater clinical benefits may be observed if a closed artery (TFG 0/1) is opened with even slow flow (TIMI grade 2 flow) compared with the improvement that might occur if an artery with TIMI grade 2 flow is converted to TIMI grade 3 flow.
- As more arteries with TIMI grade 2 flow are treated with adjunctive percutaneous coronary intervention (PCI), the prognosis associated with this flow grade may improve. The fact that patients who were treated with an inferior fibrinolytic monotherapy strategy faired so well in GUSTO V may be explained in part by the fact that these patients underwent PCI more often.  Two-year follow-up in more recent studies indicates that the survival advantage of TIMI grade 3 flow over TIMI grade 2 flow at 2 years may not be as great as it once was in the era before aggressive utilization of rescue and adjunctive (PCI).

# TIMI Flow Grade (TFG)

## TIMI Flow Grade 0
No perfusion. No antegrade flow beyond the point of occlusion.   

### Examples

## TIMI Flow Grade 1
Penetration without perfusion. Contrast material passes beyond the area of obstruction but fails to opacify the entire coronary bed distal to the obstruction for the duration of the cineangiographic filming sequence.  
This category is subdivided into:
- 1.0: dye minimally leaks past the area of obstruction.
- 1.5: dye leaks well past the area of obstruction but fails to opacify the entire coronary bed.

### Examples

## TIMI Flow Grade 2
Partial perfusion. Contrast material passes across the obstruction and opacifies the coronary bed distal to the obstruction. However, the rate of entry of contrast material into the vessel distal to the obstruction or its rate of clearance from the distal bed (or both) are perceptibly slower than its flow into or clearance from comparable areas not perfused by the previously occluded vessel (i.e. opposite coronary artery or the coronary bed proximal to the obstruction).  
This category is subdivided into:
- 2.0: TIMI 2 slow flow, dye markedly delayed in opacifying distal vasculature.
- 2.5: TIMI 2 fast flow, dye minimally delayed in opacifying distal vasculature.

### Examples

## TIMI Flow Grade 3
Complete perfusion. Antegrade flow into the bed distal to the obstruction occurs as promptly as antegrade flow into the bed proximal to the obstruction, and clearance of contrast material from the involved bed is as rapid as clearance from an uninvolved bed in the same vessel or the opposite artery.  

### Examples

## TIMI Flow Grade 4
TIMI grade 4 flow is a term developed by Dr. C. Michael Gibson, M.S., M.D. to describe hyperemic flow on a coronary arteriogram.  Hyperemic flow on a coronary arteriogram is defined qualitatitively as near instantaneous filling of the coronary artery with dye, and quantitatively as a corrected TIMI frame count < 14 frames. Hyperemic flow in a coronary artery may be due to either repayment of oxygen debt following ischemia due to a balloon inflation for instance, or distal embolization.  If it is due to distal embolization, and if impaired myocardial perfusion is present (TIMI myocardial perfusion grade 0 or TIMI myocardial perfusion grade 1), then the mortality associated with TIMI grade 4 flow is actually higher than that of TIMI grade 3 flow.  In this scenario, the hyperemic flow is a surrogate or marker of endogenous adenosine release due to distal embolization, rather than being causally related to adverse outcomes.

# The TIMI Frame Count
The TIMI flow grade, while useful, has been largely supplanted by the more quantitative measure named TIMI frame count, which is the number of frames required for dye to traverse the length of the artery. The TIMI frame count provides prognostic information independent of the TIMI Flow Grade.
For more detailed information about TIMI frame count (TFC) click here.

# TIMI Flow Grade Based on the Corrected TIMI Frame Count
The TIMI flow grade may be approximated from the raw TIMI frame count (TFC):
Note:
- There is no upper limit in CTFC for TIMI flow grade 2.
- The frame count entered in the CRF is the raw TIMI frame count (TFC)
- Corrected TIMI frame count (CTFC) can be calculated by the formula: CTFC = TFC / correction factor
- Correction factor varies depending on the infarct-related artery (see below).