Relation of Corrected Thrombolysis in Myocardial
infarction Frame Count and ST-Segment
Resolution to Myocardial tissue perfusion
After Acute Myocardial Infarction

Objectives: To evaluate myocardial tissue perfusion by corrected thrombolysis in myocardial infarction (TIMI) frame count (CTFC) and ST-segment resolution after suc­cessful percutaneous coronary intervention (PCI) in patients with acute myocardial infarction (AMI). Background: Early and sustained potency of infarct-related artery (IRA) has become the main goal of reperfusion therapy in patients with AMI. However, myocardial tissue perfusion may remain impaired even after the achievement of TIMI grade 3 flow of the epicardial artery without residual stenosis. Methods: CTFC was measured after successful PCI in 63 patients with first AMI. The extent of ST-segment resolution was recorded 1 hr after reperfusion therapy. The wall motion score index (WMSI) was assessed before and 1 month after PCI. Then we studied the correlation between CTFC, ST-segment resolution, and WMSI. Results: According to CTFC, the patients with TIMI grade 3 flow after PCI were divided into two groups: CTFC fast group and CTFC slow group. CTFC fast group had higher percentage of complete ST resolution (54.1% vs. 25,0%, P < 0,05) and lower percentage of no ST resolution (2.6% vs. 29,2%, P < 0,05). Improvement of WMSI in the CTFC fast group was significantly greater than that of the CTFC slow group (1.30 ± 0.41 vs. 0.64 ± 0.30, P < 0,05). CTFC had a significant negative correlation with the change in WMSI (r = -0,75, P < 0.01). Conclusions: Combined with ST-segment resolution, CTFC could predict risk for patients with successful reperfusion therapy after AMI and provide evidence for additional adjunctive treatment.
Key words: corrected TIMI frame count; wall motion score index; percutaneous coro­nary intervention; myocardial tissue perfusion


INTRODUCTION

Percutaneous coronary intervention (PCI) is an effective treatment to patients with acute myocardial infarction (AMI). Early and sustained potency of the infarct-related artery (IRA) has become the primary goal of reperfusion therapy in patients with AMI. The achievement of thrombolysis in myocardial infarction (TIMI) grade 3 flow in the IRA is regarded as successful reperfusion. However, increasing evidence suggests that myocardial tissue perfusion may remain impaired even after the achievement of TIMI grade 3 flow of the epicardial artery without residual stenosis. This may limit the benefits of reperfusion therapy. The recovery of microcirculatory flow is the key lo restoring the myocardial tissue perfusion. Corrected TIMI frame count (CTFC) and ST-segment elevation resolution can indirectly reflect the dysfunction of coronary microcirculation 1,2. In this study, we evaluated myocardial tissue perfusion by CTFC, the grade of ST-segment resolution and wall motion score index (WMSI) by two dimensional echocardiografhy after successful PCI (TIMI grade 3 flow and residual stenosis < 30%) in patients with AMI. The result showed that among patients with acute ST-segment elevation myocardial Infarction successfully treated by primary angioplasty, CTFC combined with ST-segment resolution may provide complementary information in the evaluation of myocardial perfusion and give additional prognostic information.

METHODS

Patient Population

We screened 70 consecutive patients who underwent primary PCI for a first ST-segment elevation AMI during the first 6 hr of symptom onset at the Shandong Provincial Hospital in Jinan, China. The diagnosis criteria of AMI were chest pain lasting more than 30 min in conjunction with persistent ST-segment elevation -> 0,1 mV in two or more contiguous leads on the 12-lead electrocardiogram (ECG) (or ->0,2 mV in leads V1 through V3) and a >2-fold increase in creatine kinase serum levels or increased serum troponin T levels. The exclusion criteria were cardiogenic shock defined as systolic blood pressure below 90 mm Hg despite conservative measurements, prior coronary artery bypass grafting, previous myocardial infarction and PCI, unsuccessful PCI defined as no antegrade flow, and/or >30% residual stenosis in the IRA. Studies with inadequate filling of the coronary arteries or visualization of the distal landmarks for frame count-ing were also excluded. We defined successful angioplasty as complete restoration of coronary artery patency with a TIMl grade 3 flow (CTFC < 40) and <30% diameter stenosis of the IRA after primary PCI.
Of the 70 patients screened, 63 had successful angioplasty and constituted our study population and no evidence of reinfarction during a l-month follow-up period. All patients gave informed consent to the study before the procedure. The institutional review board had approved the study protocol. Electrocardiograms and angiograms and echocardiograms were analyzed by blinded investigators.

Analysis of Clinical Descriptive Variables.

Variables recorded in the patients included the following: (1) clinical and demographic characteristics: age, gender, prior cardiac history, blood pressure and the heart rate at admission; (2) risk factors of coronary artery disease such as hypertension, diabetes mellitus; and 3) angiographic characteristics, which included from symptom onset to the actual performance of PTCA, culprit coronary artery, the number of diseased coronary vessels, collateral circulation, TIMI in the IRA before PCI, TIMI frame count, residual stenosis and stent implantation.

Primary Angioplasty and Stenting Procedure

Primary coronary angioplasty was performed within 6 hr after the onset of symptoms according to standard clinical protocol at our institution. Vascular access was obtained using the Judkins technique through the femo­ral approach. An initial intravenous bolus of heparin 6,000 u and additional doses of 3,000 u were given to patients during the procedure every 1 hr longer. All patients were pretreated with aspirin 300 mg and clopidogrel 300 mg. Patients who received intracoronary stents (58.7%) were subsequently treated with clopidogrel for a period of 4 weeks. (b-Adrenergic blockers and angiotensin-converting enzyme inhibitors were started according to evidence-based practice guidelines. Intracoronary nitroglycerin 200 ug were administered before CTFC counting lo preserve a state of maximum vasodilation. Time from symptom onset to PTCA (we defined elapsed time) was calculated as the time between symptom onset and first balloon inflation.

Calculation of CTFC

The TIMI frame count was measured with digital cardiac image sequence acquisitions (INNOVA 2000, GE Medical Systems, USA), The number of cine frames required for contrast to first reach standardized distal coronary artery landmarks was measured using the frame counter. The first frame used for TIMI frame counting was defined as a column of contrast fully entering the artery with anterograde motion. This occurs when the two criteria are met: (1) A column of nearly full or fully concentrated dye must extend across the entire width of (he origin of the artery and touch both borders of the origin of the artery; (2) There must be anterograde motion to the dye. The last frame counted was that in which contrast enters (but did not necessarily fill) a dislal arterial landmark. These landmarks were as follows: the first branch of the posterolateral artery in the right coronary artery (RCA); in the left circumflex (LCX) system the distal branch of the lateral left vermicular wall artery furthest from the coronary ostium; and in the left anterior descending (LAD) artery the distal bifurcation known as the "moustache", "pitch fork" or "whale's tail." The TIMI frame count of the LAD and circumflex arteries often was assessed best in either the right or left ante­rior oblique views with caudal angulation, and the RCA often was assessed test in the left anterior oblique projection with steep cranial angulation 3.

Electrocardiographic ST-Segment Resolution

Electrocardiographic tracings were obtained before PCI and at 1 hr after PCI. The ECGs were analyzed manually by at least two investigators who were