ORIGINAL ARTICLES

Predictors of Mortality at 30 Days in High-Risk Patients Treated with Direct or Rescue Stenting
for Acute Myocardial Infarction

Luigi La Vecchia, MD, Manuela Martini, MD, Maurizio Sartori, MD, Paolo Vincenzi, MD, Luigi Cischele, MD, Tiziana Righetti, MD, Renato Ometto, MD, Alessandro Fontanelli, MD
Luigi La Vecchia, MD, Manuela Martini, MD, Maurizio Sartori, MD, Paolo Vincenzi, MD, Luigi Cischele, MD, Tiziana Righetti, MD, Renato Ometto, MD, Alessandro Fontanelli, MD
Large-scale trials reported the benefits of coronary angioplasty over systemic thrombolysis for the treatment of acute myocardial infarction (AMI).1,2 More recent studies demonstrated that stenting can determine a further improvement in results over conventional balloon angioplasty.3,4 However, most of these data were obtained in selected patients so that results achievable in a broader population, including patients with more severe conditions, may be expected to be less impressive. In fact, it is known that patients who are not eligible for randomized trials have an unfavorable combination of risk factors that translates into a higher mortality.5 In cardiac catheterization facilities located in small-to-mid size centers where percutaneous revascularization cannot be offered to all AMI patients, high-risk cases are likely to be selected hypothesizing that they benefit most from an aggressive approach.6 Likewise, patients initially admitted to remote and less equipped hospitals may necessitate late revascularization in case of failed thrombolysis, thus identifying another high-risk subgroup7 that is usually neglected in published studies. Since adverse outcomes are by definition more likely to occur in high-risk conditions, it may become difficult to ascertain whether the single center involved in this treatment is providing adequate results for that particular group of patients. This concept is well appreciated when dealing with cardiogenic shock. Recent studies show how difficult it is to unequivocally demonstrate the advantages of an aggressive approach,8 while most clinicians would probably not deny such a strategy, if available, in the single patient. The definition of “high-risk” is based on observations derived from large trials9,10 and is confirmed by single-center studies11 and clinical experience. Although the relative weight of individual risk factors may vary considerably in different studies and for different endpoints, their utilization provides useful information to the reader concerning the severity profile of the patients studied as well as to compare outcomes for similar risk. Based on these concepts, we analyzed the results of coronary stenting performed in our laboratory on high-risk AMI patients in order to define the rate of fatal events in the short term, predictors of such events and possible strategies of intervention to improve results. Methods Patient population. One-hundred and twenty consecutive high-risk patients (76% male; mean age, 64 years; age range, 38–95 years) were treated with stenting for evolving AMI at our institution since 1995 by 3 operators (LL, MM, PV). The definition of high-risk was based on the presence of at least 1 of the following characteristics: age > 75 years; anterior AMI (ST segment elevation in leads V1–V6); cardiogenic shock; Killip class 3; triple-vessel disease or left main disease; cardiac arrest before intervention; left ventricular ejection fraction 20%.3 Besides the above-mentioned risk factors, other clinical, angiographic and procedural variables were recorded and analyzed. Among these are: time to reperfusion; infarct size (defined as the peak CK-MB level after the procedure); treated vessel; and procedural variables (number of inflations, inflation pressure, length of stented segment, etc.). Procedural data. Routinely, the procedure was accomplished via a femoral approach. In the earlier experience, heparin was administered as an initial bolus of 10,000 U. Subsequently, the dose of heparin was reduced to 5,000 U. In patients receiving abciximab, no further heparin was administered; in the remainder, a total dose of 100 U/kg was reached by adding a second weight-adjusted bolus when indicated. Details on safety and bleeding complications with this regimen have been previously reported.12 Intracoronary nitrates were administered routinely during the procedure; additional intracoronary thrombolytics were not used. Soft-tip steerable guidewires and monorail balloon systems were used. Stents were either bare or pre-mounted. Aspirin 160 mg and ticlopidine 500 mg for 1 month were routine treatment after stenting. The presence of a left ventricular end-diastolic pressure > 20 mmHg with persistent arterial hypotension (systolic blood pressure Statistical analysis. Data are presented as means ± one standard deviation for continuous variables and frequencies for categorical variables. Comparisons between groups were performed using a 2-tailed unpaired t-test for continuous variables and Chi-square statistics for categorical variables. Scores were compared by means of non-parametric analysis. A multivariate stepwise logistic regression analysis was performed in order to identify significant predictors of outcome. Odds ratios, 95% confidence intervals and their level of significance are provided. A p-value Baseline clinical and angiographic characteristics. The profile of the study population is illustrated in Table 1. Eighty percent of the patients had more than 1 risk factor, with a mean risk score of 2.6. One third of the patients had a previous myocardial infarction and the mean left ventricular ejection fraction was 40 ± 13%. At baseline angiography, TIMI flow was 0–1 in 81% of cases. The left anterior descending (LAD) coronary artery was by far the most frequently treated vessel (57%). The mean time elapsed from onset of chest pain to recanalization was 4.8 hours with 28% of patients treated > 6 hours. Procedural results. Procedural success (Table 1) was obtained in 105 cases (88%). Success rate increased from 84% during 1995–1997 to 91% during 1998–1999. Nine patients (8%) had a suboptimal result due to a TIMI 2 flow after stenting in the absence of significant residual stenosis. In 2 of these cases, a residual dissection was recognized. In 6 patients the procedure failed. In 3 patients, critical flow reduction with extensive thrombosis was observed after stenting and could not be reversed despite abciximab, intra-aortic balloon pumping (IABP), nitrates and verapamil (1 case). Control angiography at 24 hours revealed a fully patent vessel with TIMI 3 flow in 2 patients. Stenting was attempted in 117 patients and was successful in 115 patients (98%). The mean inflation pressure employed for stenting was 13 ± 2.5 atmospheres. Starting from November 1997, abciximab was administered in 36% of patients as a bolus followed by a 12-hour infusion. The intra-aortic balloon pump was used in 42% of cases. The indications for IABP included: cardiogenic shock; electrical or hemodynamic instability; TIMI 2 flow post-procedure; or severe multivessel disease. In most instances, it was inserted at the end of the procedure and maintained for 48 hours afterwards. Only a few patients (6% of the total) had the procedure performed while on IABP. 30-day outcome. At 30 days, twenty patients (17%) died. Of these, seventeen (85%) were in cardiogenic shock before the procedure (10 under respiratory assistance, 8 with severe electrical instability, and 9 under cardiopulmonary resuscitation). With regard to patients presenting with cardiogenic shock (n = 26), mortality was as high as 65%; a 3.2% mortality was observed in those without shock (n = 94). Although mortality was similar during 1995–1997 as compared to 1998–1999, adding up to 10 cases in each period, procedural success was obtained in only 4 of the patients that subsequently died in 1995–1997 compared to 8 patients in 1998–1999. No death was recorded after patient discharge. Comparison of risk factors, clinical characteristics and procedural variables in survivors versus non-survivors is illustrated in Table 2. Non-survivors showed a significantly higher prevalence of shock, pre-hospital cardiac arrest and suboptimal result. In addition, they had significantly older age, higher risk score and lower left ventricular ejection fraction. Baseline clinical and angiographic characteristics were also compared in patients treated with primary and rescue stenting. The only significant difference between the 2 groups was a longer pre-coronary time in rescue stenting (5.9 ± 2.9 hours versus 3.7 ± 2.9 hours; p Conclusion. Thirty-day mortality in high-risk patients treated with stenting for AMI at our institution is determined mostly by cardiogenic shock. Despite the presence of other significant risk factors, a 3.2% mortality has been achieved in the remaining patients. Rescue stenting is not associated “per se” with an increased mortality compared to primary stenting. Although we consider these results acceptable, we feel that they may be improved by increasing activity, facilitating access to the catheterization laboratory and optimizing procedural success rate. These goals hopefully will translate into a reduced event rate in the short term for both primary and rescue procedures.
References
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