ECG-Guided Immediate Intervention at the Time of Primary PCI

To Reduce Door-to-Balloon Time in ST-Elevation Myocardial Infarction Patients

ABSTRACT: Background. In ST-segment elevation acute myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PCI), all efforts must be made to improve door-to-balloon (DTB) times. This study was designed to assess the impact of electrocardiographic-guided immediate intervention (EGII) without performing a complete coronary evaluation on DTB times and clinical outcomes of STEMI patients treated with primary PCI. Methods. Consecutive STEMI patients undergoing primary PCI at Laval Hospital between May 2006 and August 2007 were considered for inclusion. Patients with thrombolysis in myocardial infarction (TIMI) 2–3 flow in the culprit vessel on initial angiography and patients with previous coronary bypass surgery were excluded from the analysis. The primary evaluation was DTB time. Clinical outcomes consisted of cardiac death, reinfarction, revascularization or stroke. Results. Two hundred seventy-nine (279) patients were included in the present analysis. Eighty-seven (87) patients underwent EGII (Group 1) and 192 underwent PCI after a complete angiographic diagnostic evaluation (Group 2). Median catheterization laboratory door-to-balloon time was 21 minutes in Group 1 and 25.5 minutes in Group 2 (p Methods Population. The study population consisted of patients who underwent primary PCI for STEMI at Québec Heart and Lung Institute (QHLI) between May 2006 and August 2007. Acute STEMI was defined as chest pain or equivalent symptoms at rest > 30 minutes, with either ST-segment elevation in > 2 contiguous leads (> 2 mm in the precordial lead, > 1 mm in the limb lead), ST-segment depression > 1 mm in the precordial leads, new or presumed new left bundle-branch block (LBBB). Patients who received fibrinolytic therapy, patients who underwent previous coronary artery bypass grafting (CABG) and those with thrombolysis in myocardial infarction (TIMI) 2–3 flow in the culprit vessel on initial angiography were excluded from the analysis. All patients were treated with aspirin > 320 mg unless allergic and received either heparin or enoxaparin. Patients were classified in two groups: Group 1 consisted of patients for whom the intention of the operator was to perform immediate intervention of the culprit vessel without undergoing a full diagnostic angiographic routine (EGII). In these patients, the operator started the intervention using an angioplasty guiding catheter to intervene on the presumed culprit vessel as suggested by the 12-lead electrocardiogram (ECG). Group 2 consisted of patients who underwent PCI after the operator performed a complete diagnostic coronary angiogram with or without a ventriculogram. Group 2 also includes patients for whom the operator chose to perform coronary angiography of the culprit vessel with a guiding catheter after imaging the opposite coronary artery with a diagnostic catheter. The choice of the procedural strategy was left at the discretion of the performing physicians. Group differentiation was based on procedure logs and by reviewing video recordings of the procedures. Data management. Clinical characteristics and important time points were recorded prospectively and entered in an electronic database. The time points considered were: time of symptoms onset, time of arrival at the initial hospital (first-door time), time of first (admission) ECG, time of first qualifying ECG, time of arrival in the catheterization laboratory and time of first device activation or achievement of TIMI 2 or 3 flow in the culprit vessel (whichever occurred first). Angiographic evaluation. TIMI flow in the culprit vessel was evaluated by two investigators who reviewed all coronary angiograms. Procedural success was defined as TIMI 2 or 3 flow in the culprit vessel and a residual stenosis of 1 mm and lasting for ≥ 30 minutes and/or either CK-MB or troponin re-elevation above the upper limit of normal and above the previous value, provided cardiac enzymes were declining after the index MI peak. Revascularization was defined as any unplanned PCI performed for recurrent symptoms. Stroke was defined as a neurologic deficit lasting more than 24 hours confirmed by a brain imaging study and/or a clinical diagnosis made by a neurologist or an internist. Statistical analysis. Data are presented as count (%) for categorical variables and median (25th, 75th percentile) for continuous variables. Time delays, angiographic success and clinical outcomes of patients in Group 1 were compared to those of patients in Group 2. Differences in means were assessed with the Student’s T-test or the Wilcoxon rank sum test depending on variable distribution. Multiple regression analysis was also performed to adjust for differences in clinical and procedural characteristics. Chi-square tests and Fisher’s exact test were used to assess differences in proportions. A Kaplan-Meier analysis was performed and the log-rank test was used to assess differences in time to cardiac death between the two groups. The Cox proportional hazard model was used to adjust for differences in baseline characteristics. Variables included in the model were those of the Zwolle risk score.5 All p-values Results Baseline characteristics. During the study period, 449 patients were treated with primary PCI for a STEMI at Laval Hospital. Of these, 279 met the inclusion criteria. The operators intended EGII in 87 patients (31%) (Group 1). In this group, the presumed occluded coronary artery was the actual culprit vessel in 83 (95%) patients. A complete angiographic evaluation was performed before PCI in the remaining 192 patients. There were no significant differences between the two groups in terms of clinical and procedural characteristics (Tables 1 and 2). Treatment delays. Relevant time points were available for all patients undergoing PCI. The time from catheterization laboratory arrival to vascular access was similar in both groups. In Group 2, complete diagnostic evaluation was performed in 7 minutes. Catheterization laboratory DTB time was 21 minutes in Group 1 compared to 25.5 minutes in Group 2, a 4.5-minute absolute reduction. The median DTB time was 80 minutes in Group 1 compared to 90 minutes in Group 2 (p = 0.01; Table 3.). DTB time was ≤ 90 minutes in 63% of patients in Group 1 compared to 49% of patients in Group 2 (p = 0.04; Table 3.). After adjusting for baseline characteristics, EGII remained an independent predictor of DTB time (p = 0.01). Patients referred for coronary artery bypass graft (CABG) surgery. During the course of the study, 3 STEMI patients referred for coronary angiography did not undergo coronary angioplasty. One patient presented with anterior MI. In this patient, the operator initially performed an angiogram of the right coronary artery (RCA), which revealed a moderate stenosis. The left coronary angiogram revealed a severe stenosis of the left main and an occlusion of the left anterior descending artery. This patient was referred for urgent CABG. The second patient presented with ST-elevation in the inferior leads. The operator performed an angiogram of the RCA with a guiding catheter. No severe stenosis was observed in the RCA. Coronary angiography of the left system revealed a severe stenosis of the left main. This patient underwent CABG 2 days after coronary evaluation. The last patient presented in cardiogenic shock. An echocardiogram was performed before coronary angiography and revealed a ventricular septal defect and mitral insufficiency. This patient was referred for urgent cardiac surgery. During the course of the study, no mechanical complications were diagnosed by ventriculography. Follow up. In-hospital and 30-day follow up was available for all patients. Long-term follow up was available for 94% of the studied population. The average length of follow up was 10.8 ± 2.9 months and was identical in each group. One-year event rates are presented in Table 4. There was no difference in unadjusted survival between Group 1 and Group 2 (p = 0.11) (Figure 1). Adjusting for differences in baseline characteristics yielded similar results (p = 0.31). Discussion This study suggests that a strategy of EGII improves DTB times compared to the standard approach of obtaining all angiographic views before attempting PCI. This reduction in DTB time translated to a higher proportion of patients being treated within the recommended 90-minute delay in Group 1 compared to Group 2. In the present study, there was a small numeric difference observed between diagnostic evaluation time and total reduction in DTB time. This difference may be explained by differences in treatment delays that occurred prior to catheterization laboratory arrival and/or by differences in the time needed to perform the angioplasty itself. Because this is a nonrandomized study, small differences in treatment delays not explained by increased diagnostic evaluation time between the two groups may be observed. However, the impact of these differences on DTB time reduction was marginal. In fact, neither the difference in first door-to-cath lab door delay nor the guiding catheter-to-balloon delay between the two groups was significant. As a result, the significant reduction in DTB time observed was mainly the result of a cut in diagnostic evaluation time. Although the present study suggests that EGII may be associated with a 6% reduction in total mortality, it is unlikely that this was solely the effect of shortened treatment delays in the catheterization laboratory. In fact, recent data suggest that each 10-minute decrease in DTB time, as seen in the present study, results in a more modest 0.16–0.24% absolute decrease in mortality.2,3 Because of the nonrandomized design of the present analysis, differences in clinical characteristics are more likely responsible for this apparent mortality reduction. Although differences in infarct location and duration of symptoms before presentation cannot explain the survival divergence, other factors not accounted for are most probably implicated. The trend towards a higher proportion of anterior wall MIs in Group 1 would tend to minimize the observed mortality difference. The benefits associated with shortened treatment delay are greatest in patients presenting within 3 hours of symptom onset.6 In this setting, EGII has the potential to improve outcomes in STEMI patients since myocardial salvage is still possible. Since mechanical complications such as ventricular septal defect or severe mitral regurgitation seldom occur early in the course of a MI, EGII is an interesting option in these patients. On the other hand, in patients presenting with TIMI 2 or 3 flow, it is reasonable to take adequate time to perform a complete diagnostic evaluation before embarking on PCI. Possible objections to EGII include the need to rule out severe 3-vessel disease and the need to make an early diagnosis of severe mitral regurgitation or ventricular septal defect. However, even in these disastrous scenarios, one could argue that most patients will gain from early flow restoration with PCI before proceeding to surgery. Also, in this era of aggressive upfront antiplatelet therapy with clopidogrel and/or glycoprotein IIb/IIIa inhibitors, postponing CABG, whenever possible, is probably a wise choice. Following this logic, completing the diagnostic coronary angiographic views and ventriculography after completion of PCI will not compromise outcomes in these patients and will not interfere with the possibility of delayed CABG. Study limitations. In the present study, patients were not randomly assigned to either treatment strategy. Since the decision to perform EGII was left to the discretion of the interventional cardiologist, some confounding factors not accounted for may be present and may have biased the results. In particular, infarct size and ejection fraction were not available for all patients and could not be used in the risk-adjustment models. Due to its small sample size, this study had limited power to detect differences in clinical outcomes. Finally, this study was conducted in a high-volume primary PCI tertiary care center in stable patients without suspicion of mechanical complications or left main disease. Therefore, the results may not be generalizable to different clinical settings or scenarios. In conclusion, this study suggests that EGII is safe and feasible and may contribute to significantly reducing DTB time in STEMI patients. However, both strategies were equivalent regarding patient outcomes. Before this approach can be endorsed widely, demonstration of improved clinical outcomes in an adequately-powered randomized clinical trial is warranted.

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