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Angioplasty Guidewire Velocity: A New Simple Method to Calculate Absolute Coronary Blood Velocity and Flow
Angioplasty Guidewire Velocity: A New Simple Method to Calculate Absolute Coronary Blood Velocity and Flow C. Michael Gibson, MD, J. Theodore Dodge Jr, MD, Mukesh Goel, MD, Eyas N. Al-Mousa, MD, Michael Rizzo, BS, Christine McLean, BS, Kathryn Ryan, Anthony Sparano, BS, Susan J. Marble, MS, William L. Daley, MD, Christopher P. Cannon, MD, and Elliott M. Antman, MD
BS,
The Thrombolysis In Myocardial Infarction (TIMI) frame count is a relative index of coronary flow that measures time by counting the number of frames required for dye to travel from the ostium to a standardized coronary landmark in a cineangiogram filmed at a known speed (frames/s). We describe a new method to measure distance along arteries so that absolute velocity (length 4 time) and absolute flow (area 3 velocity) may be calculated in patients undergoing percutaneous transluminal coronary angiography (PTCA). After PTCA, the guidewire tip is placed at the coronary landmark and a Kelly clamp is placed on the guidewire where it exits the Y-adapter. The guidewire tip is then withdrawn to the catheter tip and a second Kelly clamp is placed on the wire where it exits the Y-adapter. The distance between the 2 Kelly clamps outside the body is the distance between the catheter tip and the anatomic landmark inside the body. Velocity (cm/s) may be calculated as this distance (cm) 4 TIMI frame count (frames) 3 film frame speed (frames/s). Flow (ml/s) may be calculated
by multiplying this velocity (cm/s) and the mean crosssectional lumen area (cm2) along the length of the artery to the TIMI landmark. In 30 patients, velocity increased from 13.9 6 8.5 cm/s before to 22.8 6 9.3 cm/s after PTCA (p <0.001). Despite TIMI grade 3 flow both before and after PTCA in 18 patients, velocity actually increased 38%, from 17.0 6 5.4 to 23.5 6 9.0 cm/s (p 5 0.01). For all 30 patients, flow doubled from 0.6 6 0.4 ml/s before to 1.2 6 0.6 ml/s after PTCA (p <0.001). In the 18 patients with TIMI grade 3 flow both before and after PTCA, flow increased 86%, from 0.7 6 0.3 to 1.3 6 0.6 ml/s (p 5 0.001). Distance along coronary arteries (length) can be simply measured using a PTCA guidewire. This length may be combined with the TIMI frame count to calculate measures of absolute velocity and flow that are sensitive to changes in perfusion. TIMI grade 3 flow is composed of a range of velocities and flows. Q1997 by Excerpta Medica, Inc. (Am J Cardiol 1997;80:1536 –1539)
he binary nature of clinical decision making, such as whether to intervene and treat a lesion or T whether to manage a patient conservatively has col-
rather than qualitative, objective rather than subjective, and it is a continuous rather than a categorical variable. A potential limitation of the TIMI frame count is that as a measure of time it is an index of coronary blood flow rather than an absolute measure of coronary velocity. We describe a new method to measure distance along arteries so that absolute velocity (length 4 time) and absolute flow (area 3 velocity) may be calculated in patients undergoing percutaneous transluminal coronary angioplasty (PTCA).
ored our perception of coronary artery disease pathophysiology. Indeed, lesion severity, disease progression, and restenosis have all at one time been perceived to be discrete phenomena, and likewise coronary blood flow has been categorized as either normal or delayed.1 In keeping with this dichotomous perception of coronary blood flow, the Thrombolysis In Myocardial Infarction (TIMI) trial study group proposed the TIMI flow grade system in 1985.2 Although a valuable method to classify flow, this method has several important limitations.3 To overcome these limitations, we developed a technique called the TIMI frame count in which the number of frames needed for dye to reach standardized distal landmarks is counted.3 In contrast to the conventional TIMI flow grade system, the TIMI frame count is quantitative From the Cardiovascular Division of the Department of Medicine, the Brigham and Women’s Hospital and West Roxbury Veteran’s Affairs Medical Center, Harvard Medical School, Boston, Massachusetts. Manuscript received March 18, 1997; revised manuscript received and accepted September 16, 1997. Address for reprints: C. Michael Gibson, MD, Chief Cardiovascular Division, West Roxbury Veterans Affairs Medical Center, 1400 VFW Parkway, West Roxbury, Massachusetts 02132.
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©1997 by Excerpta Medica, Inc. All rights reserved.
METHODS
Patient group: The PTCA guidewire technique was applied to 30 culprit arteries of 29 patients undergoing PTCA at the West Roxbury VA Medical Center. Patients were men aged 60 6 10 years and had a body surface area of 2.03 6 0.18 m2. Left ventricular size was normal in 25, mild to moderately dilated in 2, and unknown in 2 (no ventriculography or echocardiography performed). Left ventriculograms performed in 17 patients revealed ejection fractions of 64 6 9% and left ventricular end-diastolic volume indexes of 69 6 15 ml/m2. The indication for PTCA was stable angina in 13, chest pain after myocardial infarction in 5, unstable angina in 4, recent non–Q-wave myocardial infarction in 4, congestive heart failure in 2, and acute 0002-9149/97/$17.00 PII S0002-9149(97)00747-9
FIGURE 1. Method of measuring the distance from the ostium to the distal TIMI frame count landmark of the coronary artery using the guidewire pullback technique. The end of the guidewire is placed at the TIMI frame count landmark and its position is confirmed using a dye injection. The first Kelly clamp (#1) should then be attached where the guidewire exists the Y-adapter. The guidewire is then withdrawn to the ostium of the artery. A second Kelly clamp (#2) should now be attached to the guidewire as it exits the Yadapter. The wire is then withdrawn while keeping both the Kelly clamps in place. Outside the body, the distance from the proximal edge of the first Kelly clamp to the proximal edge of the second Kelly clamp is then measured and is the same distance to the TIMI frame count landmark from the origin of the artery.
myocardial infarction in 1. Nine culprit left anterior descending arteries, 15 culprit right coronary arteries, and 6 culprit left circumflex arteries were studied. Patients were not routinely treated with nitrates unless clinical symptoms warranted treatment. Assessment of TIMI flow grades: The TIMI flow grade was assessed at the angiographic core laboratory as previously defined.3 To evaluate coronary flow objectively as a continuous quantitative variable, the number of cine frames required for contrast to first reach standardized distal coronary landmarks in the culprit artery (the TIMI frame count) was measured using the cine viewer frame counter.3 The first frame in the TIMI frame count is defined by a column of near or fully concentrated dye extending across at least 70% of the arterial lumen and with anterograde dye motion. The last frame counted is that in which dye enters (but does not necessarily fill) a standard distal landmark in the artery. Measurement of length to the TIMI frame count landmark using the PTCA guidewire: Ascertainment of the
PTCA guidewire velocity requires no major departure from routine clinical practice. The wire is positioned distally at the branch of the parent artery containing the TIMI landmark: at the first branch of the right posterolateral branch if a lesion is located in the right coronary artery, at the last branch of the longest obtuse marginal branch containing the lesion in the dye path, and in the left anterior descending artery at which the distal bifurcation is also known as the ‘‘moustache,’’ ‘‘pitch fork,’’ or ‘‘whales tail.’’ After the final PTCA balloon inflations are performed, the guidewire tip is placed at the TIMI frame count landmark. The wire need not enter the landmark, but is just
placed at the origin of the branch used for TIMI frame counting. A Kelly clamp (clamp 1) is placed on the guidewire where it exists the Y-adapter (Figure 1). The wire is then withdrawn to the catheter tip. A second Kelly clamp (clamp 2) is then placed on the wire where it exits the Y-adapter. The distance from the proximal edge of the first clamp to proximal edge of the second clamp is measured. This measured distance outside the body is the distance from the catheter tip to the distal landmark inside the body. Flow was assessed after removal of the guidewire. Use of the TIMI frame count to determine absolute velocity: By counting the number of frames, one can
determine the time in seconds required for the dye to travel a given length of artery when the film speed is 30 frames/s using equation (1): Time ~s! 5 observed frames 3
1 second 30 frames
(1)
This measurement of time can then be combined with the distance to the landmark to calculate velocity using the following generalized formula (1) for any film acquisition rate: Velocity ~cm/s! 5
Distance separating Kelly clamps ~cm! Observed frames ~s! Frames acquired per second
(2)
Determination of flow (ml/s): Absolute flow (ml/s) can be calculated by multiplying the mean crosssectional lumen area (cm2) along the length of the artery to the TIMI landmark times the velocity. The
CORONARY ARTERY DISEASE/CALCULATING CORONARY BLOOD FLOW
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dye velocities and flows that constitute TIMI grade 3 flow. Even if 2 PTCA strategies result in the same proportion of TIMI grade 3 flow, there may Before After No. be a difference in the velocities that TIMI 0/1 n (%) 3 (10%) 0 (0%) constitute TIMI grade 3 flow. The TIMI 2 n (%) 7 (23%) 3 (10%) range of velocities that constitute difTIMI 3 n (%) 20 (67%) 27 (90%) ferent TIMI flow grades has also reCorrected TIMI frame count 35.3 6 30.0 16.4 6 7.5 Median 30 15 30 cently been described in a small Wire length (cm) 12.5 6 2.6 30 number of patients using intracoroPTCA guidewire velocity (cm/s) 13.9 6 8.5 22.8 6 9.3‡ 30 nary Doppler velocity wires.4 PTCA guidewire velocity within 17.0 6 5.4 23.5 6 9.0* 18 An advantage of the PTCA guideTIMI grade 3 flow (cm/s) PTCA guidewire flow (ml/s) 0.6 6 0.4 1.2 6 0.6‡ 30 wire velocity is that it is a continuous PTCA guidewire flow within TIMI 0.7 6 0.3 1.3 6 0.6† 18 variable that simplifies the reporting grade 3 flow (ml/s) of data as a single number (rather 2 Mean lumen area (mm ) 4.4 6 1.8 5.7 6 1.9 28 than 4 categories using the flow *p 5 0.01 comparing pre- and post-PTCA values; †p 5 0.001 comparing pre- and post-PTCA values; grade system), and it allows more ‡ p ,0.001 comparing pre- and post-PTCA values. powerful statistical analyses to be Values are expressed as mean 6 SD except where stated otherwise. performed. Whereas there was only a trend toward an improvement in flow after PTCA when the TIMI flow mean cross-sectional lumen area may be obtained by grade system was used, the corrected TIMI frame using quantitative coronary arteriography to measure count, the PTCA guidewire velocity, and the PTCA the diameter at every point along the artery and then guidewire flow were all much more statistically powerful in this small dataset. Furthermore, we found that assume a circular lumen cross section. Statistics: All values are expressed as mean 6 SD despite having TIMI grade 3 flow before and after and parametric tests such as Student’s t test or analysis PTCA, coronary flow calculated using the PTCA of variance were used to compare normally distributed guidewire technique actually increased by 86% in these patients. continuous variables. An intracoronary Doppler velocity wire (Cardiometrics Inc. Mountain View, California)4,5 can be RESULTS Angiographic results: The rate of TIMI grade 3 flow used to determine absolute velocity in coronary artertended to improve from 67% before to 90% after ies; however, its use has several limitations.1,5 VelocPTCA (p 5 0.06). The corrected TIMI frame count ity determinations are dependent upon coaxial posiimproved significantly after PTCA (a decrease from tioning of the wire and are best obtained in straight 35.3 6 30.2 to 16.4 6 7.5 frames (p ,0.001, n 5 30) arteries. To compare data at 2 time points, care must (Table I). Likewise, the velocity increased from be taken to position the wire at the same location, 13.9 6 8.5 cm/s before to 22.8 6 9.3 cm/s after PTCA which can be difficult. Each wire is fairly expensive, (p ,0.001) (Table I). In 18 patients who had TIMI can be used only once, and a sizeable initial investgrade 3 flow both before and after PTCA, the velocity ment is required to buy the central control module. actually increased 38%, from 17.0 6 5.4 to 23.5 6 9.0 There is a need for an inexpensive, quick, and cm/s (p 5 0.01). In the entire cohort of 30 arteries, the practical method of assessing coronary velocity in flow doubled from 0.6 6 0.4 ml/s before to 1.2 6 0.6 interventional trials and in clinical practice. Some of ml/s after PTCA (p ,0.001) (Table I). Again, despite the potential advantages to calculating coronary veTIMI grade 3 flow both before and after PTCA in 18 locity and flow using the PTCA guidewire technique patients, coronary flow increased by 86%, from 0.7 6 include the fact that any wire from any manufacturer 0.3 to 1.3 6 0.6 ml/s (p 5 0.001) (n 5 18). The may be used to cross difficult lesions, and no expense maximum displacement of the PTCA guidewire tip is added to the cost of PTCA (aside from that of a ruler between systole and diastole was 0.20 6 0.18 cm and 2 disposable Kelly clamps). (a maximum displacement of 1.6% 6 1.6% of the The TIMI frame count is essentially a measure of total arterial length, n 5 20). time (TIMI frame count/30 5 seconds). Neomoto et al6 recently found a correlation coefficient of 0.73 (p ,0.005), relating the time for dye to go down the DISCUSSION We report here an extension of the TIMI frame artery and average flow velocity by Doppler velocity count method (which measures time) to include the wire. Kern et al4 reported a coefficient correlation of use of the PTCA guidewire to measure coronary artery 0.45 (p 5 0.02) between the ‘‘angiographic cine length to arrive at absolute velocity (length/time 5 frames-to-opacification count’’ and Doppler velocity cm/s). Because both primary PTCA and newer throm- wire data. In these comparisons of velocity and frame bolytic agents may achieve a higher incidence of TIMI counting or time, no correction was made for the grade 3 flow, a categorical scale may fail to distin- longer lengths of left anterior descending arteries or guish the true superiority of 1 strategy over another the variability in artery length from patient to patient. due to the inability to distinguish among the range of Because the PTCA guidewire velocity technique uses TABLE I Angiographic Data Before and After PTCA
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the directly measured length of an artery, the correlations would be expected to be better than that found between Doppler flow wire velocity and unadjusted frame counts. The intracoronary Doppler wire clearly is a versatile tool with which peak flow, mean flow, coronary flow reserve, and other measures of coronary blood flow physiology can be determined,4,5 whereas the PTCA guidewire velocity technique may be limited to determining mean velocity and flow. Comparison of these 2 techniques in different clinical syndromes is needed, but it should be borne in mind that they measure different velocities: the method described here measures mean velocity along the entire length of the artery, while a Doppler velocity technique measures velocity at a single point in the artery. This technique can be adapted to calculate realtime absolute velocity in the cardiac catheterization laboratory by using newly developed PTCA guidewires containing radio-opaque markers such as the Stabilizer™ Marker Wire (Cordis Corporation, Miami, Florida).1 These wires can be used to measure distance (i.e., the number of marker bands traversed) and the frame count can be used to measure time, allowing the simple calculation of velocity during a procedure. Study limitations: Just as with Doppler flow wires, not all anatomy may be suitable for study using this technique, particularly beyond total occlusions in vessels. Whereas the PTCA guidewire velocity method can be applied to straight or curved vessels, it must be noted that very tortuous anatomy may prevent distal placement of guidewires and that nonfloppy wires may straighten and/or kink tortuous arteries. Even if the guidewire cannot be placed at the distal TIMI landmark, however, the number of frames for dye to traverse the length of the wire wherever it is positioned can still be used to calculate mean velocity. While the length of the wire may be foreshortened on the angiogram, its true length is measured outside the
body where foreshortening is not present. Variability in the corrected TIMI frame count has been reported as 5 frames in acute myocardial infarction (0.16 second in time), and the PTCA wire may be displaced by approximately 2 mm relative to the origin of the landmark during the cardiac cycle. Conclusions: A PTCA guidewire can be used to measure the distance dye travels, and the number of frames can be counted to estimate the time required for dye to travel that distance. Knowledge of time and distance, coronary artery blood velocity may be calculated. When quantitative coronary angiography is used to measure mean lumen area, absolute coronary blood flow may be calculated. Although there was only a trend toward an improvement in flow after PTCA when the TIMI flow grade system was used, as continuous variables, the TIMI frame count, the PTCA guidewire velocity, and the PTCA guidewire flow were all much more statistically powerful in this small dataset. TIMI grade 3 flow is composed of a range of velocities.
1. Dotani I, Dodge TJ, Goel M, Al-Mousa EN, McLean C, Rizzo MJ, Ryan K, Vatner R, Marble SJ, Daley WL, Gibson CM. New techniques in the angiographic analysis of coronary flow. J Interv Cardiol 1996;9:429 – 444 2. The TIMI Study Group. The thrombolysis in myocardial infarction (TIMI) trial. N Engl J Med 1985;312:932–936 3. Gibson CM, Cannon CP, Daley WL, Dodge JT, Alexander B, Marble SJ, McCabe CH, Raymond L, Fortin T, Poole WK, Braunwald E, for the TIMI 4 study group. The TIMI frame count: a quantitative method of assessing coronary artery flow. Circulation 1996;93:879 – 888 4. Kern MJ, Moore JA, Aguirre FV, Bach RG, Caracciolo EA, Wolford T, Khoury AF, Mechem C, Donohue TJ. Determination of angiographic (TIMI grade) blood flow by intracoronary Doppler flow velocity during acute myocardial infarction. Circulation 1996;94:1545–1552 5. Doucette JW, Corl PD, Payne HM, Flynn AE, Goto M, Nassi M, Segal, J. Validation of a Doppler guide wire for intravascular measurement of coronary artery flow velocity. Circulation 1992;85:1899 –1911. 6. Neomoto T, Kimura K, Shimizu T, Mochida Y, Kosuge M, Kuji N, Ishikawa T, Miyazaki N, Tochikubo O, Ishii M. Coronary artery flow velocity waveform in acute myocardial infarction with angiographic no-reflow (abstr). Circulation 1995;92(suppl I):I-325.
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BS,
The Thrombolysis In Myocardial Infarction (TIMI) frame count is a relative index of coronary flow that measures time by counting the number of frames required for dye to travel from the ostium to a standardized coronary landmark in a cineangiogram filmed at a known speed (frames/s). We describe a new method to measure distance along arteries so that absolute velocity (length 4 time) and absolute flow (area 3 velocity) may be calculated in patients undergoing percutaneous transluminal coronary angiography (PTCA). After PTCA, the guidewire tip is placed at the coronary landmark and a Kelly clamp is placed on the guidewire where it exits the Y-adapter. The guidewire tip is then withdrawn to the catheter tip and a second Kelly clamp is placed on the wire where it exits the Y-adapter. The distance between the 2 Kelly clamps outside the body is the distance between the catheter tip and the anatomic landmark inside the body. Velocity (cm/s) may be calculated as this distance (cm) 4 TIMI frame count (frames) 3 film frame speed (frames/s). Flow (ml/s) may be calculated
by multiplying this velocity (cm/s) and the mean crosssectional lumen area (cm2) along the length of the artery to the TIMI landmark. In 30 patients, velocity increased from 13.9 6 8.5 cm/s before to 22.8 6 9.3 cm/s after PTCA (p <0.001). Despite TIMI grade 3 flow both before and after PTCA in 18 patients, velocity actually increased 38%, from 17.0 6 5.4 to 23.5 6 9.0 cm/s (p 5 0.01). For all 30 patients, flow doubled from 0.6 6 0.4 ml/s before to 1.2 6 0.6 ml/s after PTCA (p <0.001). In the 18 patients with TIMI grade 3 flow both before and after PTCA, flow increased 86%, from 0.7 6 0.3 to 1.3 6 0.6 ml/s (p 5 0.001). Distance along coronary arteries (length) can be simply measured using a PTCA guidewire. This length may be combined with the TIMI frame count to calculate measures of absolute velocity and flow that are sensitive to changes in perfusion. TIMI grade 3 flow is composed of a range of velocities and flows. Q1997 by Excerpta Medica, Inc. (Am J Cardiol 1997;80:1536 –1539)
he binary nature of clinical decision making, such as whether to intervene and treat a lesion or T whether to manage a patient conservatively has col-
rather than qualitative, objective rather than subjective, and it is a continuous rather than a categorical variable. A potential limitation of the TIMI frame count is that as a measure of time it is an index of coronary blood flow rather than an absolute measure of coronary velocity. We describe a new method to measure distance along arteries so that absolute velocity (length 4 time) and absolute flow (area 3 velocity) may be calculated in patients undergoing percutaneous transluminal coronary angioplasty (PTCA).
ored our perception of coronary artery disease pathophysiology. Indeed, lesion severity, disease progression, and restenosis have all at one time been perceived to be discrete phenomena, and likewise coronary blood flow has been categorized as either normal or delayed.1 In keeping with this dichotomous perception of coronary blood flow, the Thrombolysis In Myocardial Infarction (TIMI) trial study group proposed the TIMI flow grade system in 1985.2 Although a valuable method to classify flow, this method has several important limitations.3 To overcome these limitations, we developed a technique called the TIMI frame count in which the number of frames needed for dye to reach standardized distal landmarks is counted.3 In contrast to the conventional TIMI flow grade system, the TIMI frame count is quantitative From the Cardiovascular Division of the Department of Medicine, the Brigham and Women’s Hospital and West Roxbury Veteran’s Affairs Medical Center, Harvard Medical School, Boston, Massachusetts. Manuscript received March 18, 1997; revised manuscript received and accepted September 16, 1997. Address for reprints: C. Michael Gibson, MD, Chief Cardiovascular Division, West Roxbury Veterans Affairs Medical Center, 1400 VFW Parkway, West Roxbury, Massachusetts 02132.
1536
©1997 by Excerpta Medica, Inc. All rights reserved.
METHODS
Patient group: The PTCA guidewire technique was applied to 30 culprit arteries of 29 patients undergoing PTCA at the West Roxbury VA Medical Center. Patients were men aged 60 6 10 years and had a body surface area of 2.03 6 0.18 m2. Left ventricular size was normal in 25, mild to moderately dilated in 2, and unknown in 2 (no ventriculography or echocardiography performed). Left ventriculograms performed in 17 patients revealed ejection fractions of 64 6 9% and left ventricular end-diastolic volume indexes of 69 6 15 ml/m2. The indication for PTCA was stable angina in 13, chest pain after myocardial infarction in 5, unstable angina in 4, recent non–Q-wave myocardial infarction in 4, congestive heart failure in 2, and acute 0002-9149/97/$17.00 PII S0002-9149(97)00747-9
FIGURE 1. Method of measuring the distance from the ostium to the distal TIMI frame count landmark of the coronary artery using the guidewire pullback technique. The end of the guidewire is placed at the TIMI frame count landmark and its position is confirmed using a dye injection. The first Kelly clamp (#1) should then be attached where the guidewire exists the Y-adapter. The guidewire is then withdrawn to the ostium of the artery. A second Kelly clamp (#2) should now be attached to the guidewire as it exits the Yadapter. The wire is then withdrawn while keeping both the Kelly clamps in place. Outside the body, the distance from the proximal edge of the first Kelly clamp to the proximal edge of the second Kelly clamp is then measured and is the same distance to the TIMI frame count landmark from the origin of the artery.
myocardial infarction in 1. Nine culprit left anterior descending arteries, 15 culprit right coronary arteries, and 6 culprit left circumflex arteries were studied. Patients were not routinely treated with nitrates unless clinical symptoms warranted treatment. Assessment of TIMI flow grades: The TIMI flow grade was assessed at the angiographic core laboratory as previously defined.3 To evaluate coronary flow objectively as a continuous quantitative variable, the number of cine frames required for contrast to first reach standardized distal coronary landmarks in the culprit artery (the TIMI frame count) was measured using the cine viewer frame counter.3 The first frame in the TIMI frame count is defined by a column of near or fully concentrated dye extending across at least 70% of the arterial lumen and with anterograde dye motion. The last frame counted is that in which dye enters (but does not necessarily fill) a standard distal landmark in the artery. Measurement of length to the TIMI frame count landmark using the PTCA guidewire: Ascertainment of the
PTCA guidewire velocity requires no major departure from routine clinical practice. The wire is positioned distally at the branch of the parent artery containing the TIMI landmark: at the first branch of the right posterolateral branch if a lesion is located in the right coronary artery, at the last branch of the longest obtuse marginal branch containing the lesion in the dye path, and in the left anterior descending artery at which the distal bifurcation is also known as the ‘‘moustache,’’ ‘‘pitch fork,’’ or ‘‘whales tail.’’ After the final PTCA balloon inflations are performed, the guidewire tip is placed at the TIMI frame count landmark. The wire need not enter the landmark, but is just
placed at the origin of the branch used for TIMI frame counting. A Kelly clamp (clamp 1) is placed on the guidewire where it exists the Y-adapter (Figure 1). The wire is then withdrawn to the catheter tip. A second Kelly clamp (clamp 2) is then placed on the wire where it exits the Y-adapter. The distance from the proximal edge of the first clamp to proximal edge of the second clamp is measured. This measured distance outside the body is the distance from the catheter tip to the distal landmark inside the body. Flow was assessed after removal of the guidewire. Use of the TIMI frame count to determine absolute velocity: By counting the number of frames, one can
determine the time in seconds required for the dye to travel a given length of artery when the film speed is 30 frames/s using equation (1): Time ~s! 5 observed frames 3
1 second 30 frames
(1)
This measurement of time can then be combined with the distance to the landmark to calculate velocity using the following generalized formula (1) for any film acquisition rate: Velocity ~cm/s! 5
Distance separating Kelly clamps ~cm! Observed frames ~s! Frames acquired per second
(2)
Determination of flow (ml/s): Absolute flow (ml/s) can be calculated by multiplying the mean crosssectional lumen area (cm2) along the length of the artery to the TIMI landmark times the velocity. The
CORONARY ARTERY DISEASE/CALCULATING CORONARY BLOOD FLOW
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dye velocities and flows that constitute TIMI grade 3 flow. Even if 2 PTCA strategies result in the same proportion of TIMI grade 3 flow, there may Before After No. be a difference in the velocities that TIMI 0/1 n (%) 3 (10%) 0 (0%) constitute TIMI grade 3 flow. The TIMI 2 n (%) 7 (23%) 3 (10%) range of velocities that constitute difTIMI 3 n (%) 20 (67%) 27 (90%) ferent TIMI flow grades has also reCorrected TIMI frame count 35.3 6 30.0 16.4 6 7.5 Median 30 15 30 cently been described in a small Wire length (cm) 12.5 6 2.6 30 number of patients using intracoroPTCA guidewire velocity (cm/s) 13.9 6 8.5 22.8 6 9.3‡ 30 nary Doppler velocity wires.4 PTCA guidewire velocity within 17.0 6 5.4 23.5 6 9.0* 18 An advantage of the PTCA guideTIMI grade 3 flow (cm/s) PTCA guidewire flow (ml/s) 0.6 6 0.4 1.2 6 0.6‡ 30 wire velocity is that it is a continuous PTCA guidewire flow within TIMI 0.7 6 0.3 1.3 6 0.6† 18 variable that simplifies the reporting grade 3 flow (ml/s) of data as a single number (rather 2 Mean lumen area (mm ) 4.4 6 1.8 5.7 6 1.9 28 than 4 categories using the flow *p 5 0.01 comparing pre- and post-PTCA values; †p 5 0.001 comparing pre- and post-PTCA values; grade system), and it allows more ‡ p ,0.001 comparing pre- and post-PTCA values. powerful statistical analyses to be Values are expressed as mean 6 SD except where stated otherwise. performed. Whereas there was only a trend toward an improvement in flow after PTCA when the TIMI flow mean cross-sectional lumen area may be obtained by grade system was used, the corrected TIMI frame using quantitative coronary arteriography to measure count, the PTCA guidewire velocity, and the PTCA the diameter at every point along the artery and then guidewire flow were all much more statistically powerful in this small dataset. Furthermore, we found that assume a circular lumen cross section. Statistics: All values are expressed as mean 6 SD despite having TIMI grade 3 flow before and after and parametric tests such as Student’s t test or analysis PTCA, coronary flow calculated using the PTCA of variance were used to compare normally distributed guidewire technique actually increased by 86% in these patients. continuous variables. An intracoronary Doppler velocity wire (Cardiometrics Inc. Mountain View, California)4,5 can be RESULTS Angiographic results: The rate of TIMI grade 3 flow used to determine absolute velocity in coronary artertended to improve from 67% before to 90% after ies; however, its use has several limitations.1,5 VelocPTCA (p 5 0.06). The corrected TIMI frame count ity determinations are dependent upon coaxial posiimproved significantly after PTCA (a decrease from tioning of the wire and are best obtained in straight 35.3 6 30.2 to 16.4 6 7.5 frames (p ,0.001, n 5 30) arteries. To compare data at 2 time points, care must (Table I). Likewise, the velocity increased from be taken to position the wire at the same location, 13.9 6 8.5 cm/s before to 22.8 6 9.3 cm/s after PTCA which can be difficult. Each wire is fairly expensive, (p ,0.001) (Table I). In 18 patients who had TIMI can be used only once, and a sizeable initial investgrade 3 flow both before and after PTCA, the velocity ment is required to buy the central control module. actually increased 38%, from 17.0 6 5.4 to 23.5 6 9.0 There is a need for an inexpensive, quick, and cm/s (p 5 0.01). In the entire cohort of 30 arteries, the practical method of assessing coronary velocity in flow doubled from 0.6 6 0.4 ml/s before to 1.2 6 0.6 interventional trials and in clinical practice. Some of ml/s after PTCA (p ,0.001) (Table I). Again, despite the potential advantages to calculating coronary veTIMI grade 3 flow both before and after PTCA in 18 locity and flow using the PTCA guidewire technique patients, coronary flow increased by 86%, from 0.7 6 include the fact that any wire from any manufacturer 0.3 to 1.3 6 0.6 ml/s (p 5 0.001) (n 5 18). The may be used to cross difficult lesions, and no expense maximum displacement of the PTCA guidewire tip is added to the cost of PTCA (aside from that of a ruler between systole and diastole was 0.20 6 0.18 cm and 2 disposable Kelly clamps). (a maximum displacement of 1.6% 6 1.6% of the The TIMI frame count is essentially a measure of total arterial length, n 5 20). time (TIMI frame count/30 5 seconds). Neomoto et al6 recently found a correlation coefficient of 0.73 (p ,0.005), relating the time for dye to go down the DISCUSSION We report here an extension of the TIMI frame artery and average flow velocity by Doppler velocity count method (which measures time) to include the wire. Kern et al4 reported a coefficient correlation of use of the PTCA guidewire to measure coronary artery 0.45 (p 5 0.02) between the ‘‘angiographic cine length to arrive at absolute velocity (length/time 5 frames-to-opacification count’’ and Doppler velocity cm/s). Because both primary PTCA and newer throm- wire data. In these comparisons of velocity and frame bolytic agents may achieve a higher incidence of TIMI counting or time, no correction was made for the grade 3 flow, a categorical scale may fail to distin- longer lengths of left anterior descending arteries or guish the true superiority of 1 strategy over another the variability in artery length from patient to patient. due to the inability to distinguish among the range of Because the PTCA guidewire velocity technique uses TABLE I Angiographic Data Before and After PTCA
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the directly measured length of an artery, the correlations would be expected to be better than that found between Doppler flow wire velocity and unadjusted frame counts. The intracoronary Doppler wire clearly is a versatile tool with which peak flow, mean flow, coronary flow reserve, and other measures of coronary blood flow physiology can be determined,4,5 whereas the PTCA guidewire velocity technique may be limited to determining mean velocity and flow. Comparison of these 2 techniques in different clinical syndromes is needed, but it should be borne in mind that they measure different velocities: the method described here measures mean velocity along the entire length of the artery, while a Doppler velocity technique measures velocity at a single point in the artery. This technique can be adapted to calculate realtime absolute velocity in the cardiac catheterization laboratory by using newly developed PTCA guidewires containing radio-opaque markers such as the Stabilizer™ Marker Wire (Cordis Corporation, Miami, Florida).1 These wires can be used to measure distance (i.e., the number of marker bands traversed) and the frame count can be used to measure time, allowing the simple calculation of velocity during a procedure. Study limitations: Just as with Doppler flow wires, not all anatomy may be suitable for study using this technique, particularly beyond total occlusions in vessels. Whereas the PTCA guidewire velocity method can be applied to straight or curved vessels, it must be noted that very tortuous anatomy may prevent distal placement of guidewires and that nonfloppy wires may straighten and/or kink tortuous arteries. Even if the guidewire cannot be placed at the distal TIMI landmark, however, the number of frames for dye to traverse the length of the wire wherever it is positioned can still be used to calculate mean velocity. While the length of the wire may be foreshortened on the angiogram, its true length is measured outside the
body where foreshortening is not present. Variability in the corrected TIMI frame count has been reported as 5 frames in acute myocardial infarction (0.16 second in time), and the PTCA wire may be displaced by approximately 2 mm relative to the origin of the landmark during the cardiac cycle. Conclusions: A PTCA guidewire can be used to measure the distance dye travels, and the number of frames can be counted to estimate the time required for dye to travel that distance. Knowledge of time and distance, coronary artery blood velocity may be calculated. When quantitative coronary angiography is used to measure mean lumen area, absolute coronary blood flow may be calculated. Although there was only a trend toward an improvement in flow after PTCA when the TIMI flow grade system was used, as continuous variables, the TIMI frame count, the PTCA guidewire velocity, and the PTCA guidewire flow were all much more statistically powerful in this small dataset. TIMI grade 3 flow is composed of a range of velocities.
1. Dotani I, Dodge TJ, Goel M, Al-Mousa EN, McLean C, Rizzo MJ, Ryan K, Vatner R, Marble SJ, Daley WL, Gibson CM. New techniques in the angiographic analysis of coronary flow. J Interv Cardiol 1996;9:429 – 444 2. The TIMI Study Group. The thrombolysis in myocardial infarction (TIMI) trial. N Engl J Med 1985;312:932–936 3. Gibson CM, Cannon CP, Daley WL, Dodge JT, Alexander B, Marble SJ, McCabe CH, Raymond L, Fortin T, Poole WK, Braunwald E, for the TIMI 4 study group. The TIMI frame count: a quantitative method of assessing coronary artery flow. Circulation 1996;93:879 – 888 4. Kern MJ, Moore JA, Aguirre FV, Bach RG, Caracciolo EA, Wolford T, Khoury AF, Mechem C, Donohue TJ. Determination of angiographic (TIMI grade) blood flow by intracoronary Doppler flow velocity during acute myocardial infarction. Circulation 1996;94:1545–1552 5. Doucette JW, Corl PD, Payne HM, Flynn AE, Goto M, Nassi M, Segal, J. Validation of a Doppler guide wire for intravascular measurement of coronary artery flow velocity. Circulation 1992;85:1899 –1911. 6. Neomoto T, Kimura K, Shimizu T, Mochida Y, Kosuge M, Kuji N, Ishikawa T, Miyazaki N, Tochikubo O, Ishii M. Coronary artery flow velocity waveform in acute myocardial infarction with angiographic no-reflow (abstr). Circulation 1995;92(suppl I):I-325.
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