TIMI frame count (TFC)

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Overview
TIMI frame count or TFC is defined as the number of cineframes required for contrast to reach a standardized distal coronary landmark in the culprit vessel. The number is expressed based upon a cinefilming rate of 30 frames/second. Thus, a frame count of 30 would mean that 1 second was required for dye to traverse the artery.

The TIMI Frame Count is counted using an electronic frame counter. Selected anatomic endpoints (landmarks) are used for the analysis.

History
The frame count was invented by C. Michael Gibson MS. MD. It was originally referred to as the "frames to opacification" but was later renamed the TIMI frame count.

Clinical Importance
There are several limitations to the TFG classification scheme. To overcome these limitations, Gibson developed a more objective and precise index of coronary blood flow called the corrected TIMI frame count (CTFC). In this method, the number of cineframes required for dye to reach standardized distal landmarks are counted. Each frame is 1/30th of a second, and the angiogram is therefore essentially a measure of the time for dye to go down the artery. In the first frame used for TIMI frame counting, a column of dye touches both borders of the coronary artery and moves forward. In the last frame, dye begins to enter (but does not necessarily fill) a standard distal landmark in the artery. These standard distal landmarks are as follows: in the RCA, the first branch of the posterolateral artery; in the circumflex system, the most distal branch of the obtuse marginal branch, which includes the culprit lesion in the dye path; and in the LAD, the distal bifurcation, which is also known as the "moustache," "pitchfork" or "whale’s tail". These frame counts are corrected for the longer length of the LAD by dividing by 1.7 to arrive at the CTFC. Knowing the time for dye to go down the artery from the CTFC (CTFC/30=seconds), and length of the artery (either from an angioplasty guide wire or by planimetry), dye velocity (cm/s) can also be calculated in a more refined fashion. . This refined measure allows calculation of the velocity proximal and distal to the lesion.

Some of the advantages of the TIMI frame count method are as follows. In contrast to the TFG classification scheme, the CTFC is quantitative rather than qualitative, it is objective rather than subjective, it is a continuous rather than a categorical variable, and it is reproducible. The CTFC demonstrates that flow is not divided into arbitrary slow and fast categories, but rather coronary blood flow is unimodally distributed as a continuous variable. The CTFC has been shown to be quite reproducible with a 1- to 2-frame difference between observers. The CTFC is also highly correlated with other measures of flow such as Doppler velocity wire measures of coronary flow reserve, distal velocity, average peak velocity, and volumetric flow,  as well as fractional flow reserve (r=0.85)

Several technical and physiological variables may impact the CTFC    :

1. Injection force: A power injector to change the force of injection (cc/sec) from the 10th to the 90th percentile of human injection rates lowers the CTFC by only 2 frames.

2. Nitrate administration significantly increases the CTFC by 6 frames (P<0.001)

3. Dye injection at the beginning of diastole decreases the CTFC by 3 to 6 frames

4. Increasing the heart rate by 20 beats per minute significantly decreases the CTFC by 5 frames (P<0.001)

Association of the CTFC with Clinical Outcomes
Following fibrinolytic administration as well as PCI, the CTFC is related to a variety of clinical outcomes     Flow in the infarct-related artery in survivors is significantly faster than in patients who die (49.5 versus 69.6 frames; P=0.0003). In NSTEMI and STEMI, the post-PCI culprit flow among survivors is significantly faster than among those patients who died (CTFCs 20.4 versus 33.4 frames, P=0.017). Among patients undergoing PCI, the CTFC has demonstrated greater sensitivity in detecting improvements in epicardial flow compared with the use of TIMI grade 3 flow among patients treated with new device interventions and in the detection of transplant rejection.

Anatomic Endpoint in Right Coronary Artery (RCA)
The landmark used in the right coronary artery is the first branch arising from the posterior lateral extension of the right coronary artery after the origin of the posterior descending artery, regardless of the size of this branch.

This branch will often be located just distal to the bifurcation, and may be oriented either superiorly (R4U) or inferiorly (R4L).

In some cases this branch will lie further along the extension of the distal right coronary artery and will course either superiorly as the AV nodal artery (AV) or will be oriented inferiorly as the right inferior branch (RI). In the event that a very proximal posterior descending stenosis is the culprit lesion, the first branch off the posterior descending after the stenosis is the endpoint.

Infrequently, the distal portion of the posterior descending artery is supplied by a proximally arising acute marginal branch and the proximal portion of the posterior descending artery arises at the base of the heart. In these cases, it is the extension of the distal right coronary past the posterior descending at the base of the heart and not the proximal acute marginal branch that is used for determining the TIMI frame count endpoint.

In patients with left dominant anatomy, the TIMI frame count endpoint is the distal-most branch off the right coronary artery once it is no longer in the AV groove.

Anatomic Endpoint in Left Circumflex Artery (Cx)
The branch of the circumflex artery used for TIMI Frame Counting is determined as follows. The artery used for TIMI Frame Counting is the artery with the longest total distance along which dye travels in the left circumflex system and yet passes through the culprit lesion.

When the culprit lesion is proximal to two arteries with equal total dye path distances, the artery which arises more distally from the left circumflex is used.

For example when the culprit lesion is located in the proximal left circumflex, the marginal branch with the longest total dye path distance is used, regardless of whether it is the first, second or third marginal. If these second and third marginals have equal total dye path distances, the third marginal is the target artery.

The target artery is always the first marginal when the culprit lesion is in the first marginal and, likewise, always the second marginal when the culprit lesion is in the second marginal.

In left and balanced dominant systems, the target artery is no further distal than the marginal branch which lies at the border of the inferior and lateral walls, usually the 3rd or 4th marginal; inferior wall vessels are never target arteries (i.e. “wrap around” LCx). The anatomic endpoint is the distal-most branch in the target artery, regardless of the size of the branch. Usually this endpoint branch can be found at approximately the mid-point of the distal third of the artery (5/6ths the distance down the vessel from its origin), but occasionally it is just prior to the termination of the artery.

Anatomic Endpoint in Left Anterior Descending Artery (LAD)
The landmark in the LAD is the distal-most branch in the left anterior descending artery (referred to as the "pitchfork", "moustache" or "whale’s tail") usually occurs at the apex of the heart.

In a "wrap around" left anterior descending artery, the branch closest to the apex of the heart is used.

Definitions of the first and last frames used for TIMI Frame Counting
The first frame used for TIMI Frame Counting is the first frame in which dye fully enters the artery, marked by dye touching both borders of the left main or right coronary artery. Dye may initially track down a single wall of the artery as dye leaks from the catheter prior to the injection and these frames are not included in the TIMI frame count.

In the infrequent situation in which the left anterior descending artery is subselectively engaged and the left circumflex artery is the culprit vessel, the TIMI frame count begins when dye first touches both borders at the origin of the left circumflex artery. The last frame counted occurs when dye first enters the endpoint branch off the target artery.

Note that complete opacification of the target artery is not required, just initial entry of dye into the culprit artery. Often the last frame is best determined by running the cinefilm past the initial opacification of the endpoint branch and then moving frame-by-frame in reverse until the endpoint branch disappears and then advance one more frame.

The Corrected TIMI Frame Count vs the TIMI Frame Count
The raw TIMI Frame Count is the number of cineframes required for contrast to reach a standardized distal coronary landmark in the culprit vessel converted to 30 frames/second. This value is not the “Corrected TIMI Frame Count (CTFC),” which adjusts for vessel length as well. A 1.7 correction factor is used to correct the TIMI frame counts for the average greater length of the LAD, as compared with the LCx or the RCA. When this correction is applied, this is called the corrected TIMI Frame Count (CTFC). A 1.6 correction factor is used to correct the TIMI frame counts for the average greater length of SVG’s, as compared with the LCx or the RCA.

Adjusting for Different Film Speeds
30 frames/second is the standard film speed used in U.S. cardiac catheterization laboratories (more recently 30 frames/sec filming rates are widely available at international catheterization laboratories). Alternatives include 15 frames/second and 60 frames/second. The European equivalents of U.S. 30 frames/second and 15 frames/second are 25 frames/second and 12.5 frames/second, respectively. If the frame count was collected at a rate of 15 frames/second, then the frame count is multiplied by 2 to arrive at the CTFC.

Insights into the Pathophysiology of STEMI and UA/NSTEMI based upon the CTFC
One of the more interesting observations learned with the use of the CTFC is the fact that flow in nonculprit arteries in the setting of acute coronary syndromes is "abnormal." For instance, the CTFC in uninvolved arteries in acute STEMI (30.5 frames) is in fact 40% slower than normal (21 frames, P<0.001)   Adjunctive and rescue PCI following fibrinolysis restores flow in culprit vessels that is nearly identical to that of nonculprit arteries in the STEMI setting (30.5 versus 30.5 frames, p=NS), but this flow remains slower than normal (21 frames). It is notable that PCI of the culprit lesion is also associated with improvements in the nonculprit artery after the intervention in both the STEMI and UA/NSTEMI settings. Slower flow throughout all 3 arteries in STEMI is associated with a higher risk of adverse outcomes, poorer wall motion in remote territories , poorer tissue perfusion on digital subtraction angiography (DSA) , and a greater magnitude of ST depression in remote territories such as the anterior precordium in inferior MI. The basis of slowed flow in non-culprit arteries is not clear. It has been speculated that the delayed flow in the non-culprit artery may be the result of spasm in shared territories of microvasculature, or a result of global vasoconstriction mediated through either a local neurohumoral or paracrine mechanism. Gregorini et al have highlighted the importance of sympathetic storm. Consistent with this hypothesis, they have demonstrated that the CTFC and fractional wall shortening is improved in both the culprit and nonculprit arteries after administration of alpha-blockers. Willerson and others      have also demonstrated that a wide range of vasoconstrictors including thromboxane A2, serotonin, endothelin, oxygen-derived free radicals, and thrombin are all released in the setting of vessel injury, thrombosis and reperfusion. While a residual stenosis following PCI in the setting of STEMI may be responsible for the delay in flow, it is important to note that despite a minimal 13% residual stenosis and the relief of intraluminal obstruction with stent placement, flow remains persistently abnormal in 34% of stented vessels.

Washout TIMI Frame Count
The washout TIMI Frame Count is the number of frames required for dye to exit the infarct related artery (clearance of dye from the ostium to the standardized distal TIMI landmark).

In the first frame, unopacified blood occupies at least 70% of the ostium of the artery with antegrade motion down the artery. In the last frame, unopacified blood first enters (but does not completely fill) the standard distal TIMI landmark

TIMI Myocardial Frame Count (TMFC) = frame when blush is the brightest minus frame when blush first appears.

How do I pick the first frame?
In frame zero, dye touches either none of the borders or only one of the borders as shown below:



We find that in some injections dye will dribble down on border of the artery and these frames are not selected as the first frame. In frame number one, dye extends across at least 70% of the artery and moves forward as shown below:



How do I pick the last frame?
In the last frame, the dye first enters the distal landmark. This frame is included in the frame count. For example, in frame 20 in the RCA shown below, dye has not yet entered the first branch off of the posterolateral:



In frame 21 shown below, the dye has begun to enter the first branch off of the posterolateral artery. This is the last frame counted:

In frame 22, dye begins to fill more completely the distal landmark as shown below:



What are the Distal Landmarks Used for TIMI Frame Counting?
In the RCA it is the first branch off of the posterolateral artery:



In the circumflex, it is the last branch off of the most distal obtuse marginal as shown below:



In the LAD, it is the bifurcation of the LAD at the apex which is also known as the pitchfork, or the whale’s tail as shown below: