Adjunctive Mechanical Intervention To Further Improve Flow

As the previous section indicates, stand alone thrombolytic therapy faces a formidable challenge in increasing the rate of TIMI grade 3 flow beyond 60%. While there are clear angiographic benefits to rescue (opening a closed artery) and adjunctive PTCA (further dilating an open artery with TIMI grade 2 or 3 flow) as discussed above, the clinical benefits are less clear. Previously the routine use of immediate adjunctive conventional angioplasty to supplement the results of thrombolysis has not been shown to be any more efficacious than a conservative approach of deferred angioplasty (59-61). PTCA/stenting in the subgroup of patients with suboptimal TIMI 2 flow has not been fully assessed. Preliminary results from the TIMI study group have shown that in the 38 patients in which TIMI grade 2 flow was dilated, TIMI grade 3 flow was restored in 34 patients (89.5%), and the mean post-intervention CTFC was 30.8 6 26.8 frames (62). The 30-d risk of death or recurrent MI was 11.2% in patients who were medically managed for TIMI grade 2 flow (12 out of 107) and was 10.0% in those patients who were treated with PTCA/stenting for TIMI grade 2 flow (4 out of 40) (p 5 NS) (62). Thus, PTCA/stenting may not offer a major advantage in clinical outcomes over medical management. Larger randomized trials are obviously needed to ascertain the clinical benefit (if any) of mechanical intervention over medical management for TIMI grade 2 flow following thrombolysis.

If thrombolytic therapy is not effective in opening the infarct related artery, a "rescue" or "salvage" PTCA may be performed. Experience with rescue angioplasty sheds important light on the relative importance of coronary blood flow and the timing with which that flow is achieved. In the TIMI 4 trial, although successful rescue angioplasty for an occluded artery at 90 min resulted in a much higher rate of TIMI 3 flow than successful thrombolysis (86.5 vs 64.8%, p = 0.002), this higher rate of grade 3 flow was achieved later, at over 120 min after thrombolysis, and this time, delay may explain in part the higher rate of mortality (9.6%) for this strategy than successful thrombolysis (3.3%) (Fig. 8) (63).

Direct or primary angioplasty in acute MI has been demonstrated to achieve high rates of patency and TIMI grade 3 flow in several small angiographic trials (63-71). In the initial study in this area, the Primary Angioplasty in Myocardial Infarction (PAMI) investigators reported a success rate of 97.1% for primary angioplasty (64). There was a trend for patients treated with primary angioplasty to have a lower mortality rate than patients treated with thrombolysis alone (2.6 vs 6.5%, respectively, p = 0.06) in this trial. However, other randomized trials of primary angioplasty at the time, each involving less than 100 patients per treatment arm, revealed no significant difference in mortality between the two strategies (65-67).

These early comparisons of primary angioplasty with thrombolysis, however, were limited by the use of either older dosing regimens of tPA or streptokinase (SK), rather than utilizing the more efficacious regimen of front-loaded tPA. Fortunately, the most recent randomized trial in this field (the GUSTO IIb trial) overcomes many of these limitations in its comparison of direct angioplasty to front-loaded tPA in a large series of 1138 patients (68). The composite endpoint of the trial (death, reinfarction or stroke) was lower in the primary angioplasty group than the front-loaded tPA group (9.6 vs 13.7%, p = 0.03), and there was a trend for the 30-d mortality rate to also be slightly lower (5.7 vs 7.0%,p = NS) with this strategy (68). In contrast to the 90-99% success rate previously reported by primary angioplasty operators and the 84% rate reported in the GUSTO IIb trial, only 73% of patients achieved TIMI grade 3 flow following angio-plasty in this trial when the TFGs were evaluated by an independent angiographic core laboratory. Although this core laboratory rate of TIMI grade 3 flow is lower than the rate assessed by the primary PTCA operators themselves, this 73% rate of TIMI grade 3 flow following primary PTCA still compares favorably with the 60% rate reported

Thrombolytic Success

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^- 65% TIMI 3 Flow y^90Min. 3,3% Mortality

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