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Outcomes of Percutaneous Coronary Intervention Among Elderly Patients in Cardiogenic Shock: A Multicenter, Decade-Long Experienc
July 2003
Outcomes for patients with acute myocardial infarction (AMI) complicated by cardiogenic shock have improved in the setting of increased use of coronary revascularization during the 1990s.1,2 Consistent with these observations, the randomized Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock (SHOCK) trial showed a significant overall benefit for patients with cardiogenic shock treated with a strategy of early revascularization when compared with a more conservative approach.3 In contradistinction to prior registry observations,4 the SHOCK trial results were not favorable with respect to elderly shock patients undergoing early revascularization. Thus, current guidelines for treatment of patients with AMI complicated with cardiogenic shock restrict the Class I recommendation for early revascularization to those patients who are less than 75 years old.5 It is possible that clinical selection of elderly shock patients based upon lack of significant comorbidities and favorable angiographic characteristics6 may allow a more favorable outcome to be obtained with early revascularization. We utilized a decade-long experience in the Northern New England Cardiovascular Registry to identify the characteristics of elderly shock patients selected for PCI and their real world outcomes.
Methods
Study population. A total of 52,418 patients underwent PCI at the member institutions of the Northern New England Cardiovascular Disease Study Group between January 1, 1990 and December 31, 2000. This study examined the outcomes of the 310 patients (0.6%) who had PCI performed for the indication of cardiogenic shock. Of these patients, seventy-four were elderly (age >= 75 years) and these elderly shock patients were compared to non-elderly shock patients (n = 236) with respect to baseline clinical characteristics, procedural variables and hospital mortality rates. No patients were excluded from the analysis. The use of PCI for cardiogenic shock did not vary significantly between the pre-stent era (1990–1996: 0.5%) and the stent era (1997–2000: 0.7%). Data collection. Data were collected by the Northern New England Cardiovascular Diseases Study Group, a voluntary, regional consortium of physicians, allied health professionals, administrators and scientists from 8 institutions in Maine, New Hampshire, Vermont and Massachusetts. The institutions in Maine, New Hampshire and Vermont are the sole providers of coronary artery bypass graft (CABG) surgery and PCI in the region. Since 1987, this group has worked to study the process and outcomes of cardiovascular care via prospectively collected data obtained on all coronary revascularization procedures performed at these institutions. The details of the data collection methodology have been previously described.7,8 Briefly, information is collected in the following areas: demographics, past medical history, primary indication for procedure, priority of procedure, therapy, cardiac anatomy and function, procedural details and hospital outcomes. Past medical history includes information on prior CABG, PCI, AMI and comorbid conditions documented in the medical record. These comorbid conditions include congestive heart failure, chronic obstructive pulmonary disease, peripheral vascular disease, renal disease requiring dialysis and chronic renal insufficiency, defined as a creatinine > 2.0 mg/dl. Priority of revascularization procedure was classified as emergent, urgent or nonurgent, and indication of procedure was classified according to the type of coronary syndrome (i.e., stable angina, primary therapy for AMI). This included a specific indication relative to this analysis: PCI for cardiogenic shock, defined by clinical parameters (systolic blood pressure 1 Information concerning the exact timing of revascularization with respect to AMI onset was not collected, although the dates of AMI and revascularization were collected. For this reason, all patients with cardiogenic shock undergoing revascularization for the indication of shock were included, rather than only patients who had documented revascularization within 36 hours of shock onset. Coronary anatomy was defined by operators according to visual interpretations of angiograms. Severity of coronary artery disease and lesion type were classified using methods adapted from the NHLBI Coronary Artery Study Group.9 Procedural and hospital outcomes were assessed by review of the inpatient medical record. Data collection methods of the Northern New England Cardiovascular Disease Study Group have been approved by the human subjects committees of each of the participating institutions. Statistical analysis. Comparisons of characteristics between elderly and non-elderly shock patients were made using the t-test for continuous variables and the Chi-square test for categorical variables. Logistic regression was used to assess the univariate relation between patient, disease and treatment characteristics and in-hospital mortality. Indirect standardization was used to calculate adjusted mortality rates controlling for gender, renal failure, diabetes mellitus, multivessel coronary artery disease and the presence of collaterals. Independent predictors of hospital mortality were determined using multivariate logistic regression analysis including all variables found to be significant predictors of mortality (p Results Baseline characteristics. Elderly patients undergoing PCI for cardiogenic shock were significantly more likely to be female and non-smokers than non-elderly patients (Table 1). There were trends toward patients having more hypertension and prior AMIs, but less diabetes and heart failure. The 2 groups were remarkably similar with respect to rates of peripheral vascular disease, prior CABG, chronic renal insufficiency and chronic obstructive pulmonary disease. Angiographic and procedural characteristics. Elderly shock patients were significantly less likely to have a totally occluded culprit vessel at the time of initial angiography compared to the non-elderly (Table 1). There was also a trend toward them having more double-vessel and less single-vessel disease than younger patients. There were no significant differences in the location of the culprit lesion or in its features. Over two-thirds of both patient populations received stents (Table 2) at the time of PCI (during the stent era of 1997–2000). There was also no difference in the use of GP IIb/IIIa inhibitors. There was a significantly higher failure rate to cross the lesion among the elderly subgroup. Despite this, there was a trend toward a decreased use of intraaortic balloon pumps in the elderly. Hospital outcomes. Nonfatal outcomes were similar between age groups (Table 2), including an overall rate of approximately 6% for emergent CABG and an 11% rate of vascular complications. The overall hospital mortality rate was 37%. A trend was seen toward higher mortality among the elderly as compared to non-elderly shock PCI patients (46.7% versus 34.5%, respectively; p = 0.058), and these mortality rates were identical after adjustment (Figure 1). Univariate predictors of hospital survival for all patients undergoing PCI for cardiogenic shock are shown in Table 3. Survivors were significantly less likely to have diabetes, with a trend toward having less renal insufficiency and less triple-vessel disease. They were more likely to have collateral flow distal to the culprit lesion. Survival was better in patients who could receive a stent. Multivariate logistic regression analysis identified 2 independent predictors of hospital mortality during the decade-long experience: older age (odds ratio, 1.81; 95% confidence interval, 1.03–3.18; p = 0.038) and collateral vessels (odds ratio, 0.29; 95% confidence interval, 0.13–0.67; p = 0.004). A similar analysis performed during the stent era (1997–2000) identified 2 different independent predictors of hospital mortality: stenting (odds ratio, 0.37; 95% confidence interval, 0.18–0.74; p = 0.005) and diabetes mellitus (odds ratio, 2.96; 95% confidence interval, 1.37–6.38; p = 0.006). Survival improved significantly over the time period of the stent era (Figure 2).Discussion
Recent improvements in the early survival of patients hospitalized with cardiogenic shock in the United States have occurred in the setting of increased use of coronary revascularization.1,2,4,10 The randomized SHOCK trial demonstrated a trend toward improved 30-day survival and a significant improvement in 6-month survival with the use of an early revascularization strategy among patients with AMI complicated by cardiogenic shock.3 This survival advantage was not extended to elderly patients, and current recommendations for early revascularization are confined to non-elderly shock patients.5 The SHOCK trial identified a 75% hospital mortality rate among the 56 elderly patients in their study who underwent early revascularization.3 However, using data from a decade-long PCI experience in the Northern New England Cardiovascular Disease Study Group, we found that the hospital mortality for selected elderly shock patients undergoing PCI was less than 50% (Figure 1). This mortality rate of 46.7% for elderly shock patients is in fact lower than the 47–69% range of early mortality rates previously reported in multicenter registries and trials for patients of all ages with AMI complicated by cardiogenic shock,1,3,11 and suggests that it may be possible to identify selected elderly shock patients for an early revascularization strategy. Defining the real world mortality rate for elderly shock PCI patients. Age has been shown to be a significant predictor of early mortality in both registries and trials of patients with AMI complicated by cardiogenic shock,3,4,6 and our results confirm this. On the other hand, the mortality rate for elderly patients undergoing PCI for shock is 46% in this multicenter registry study, and not the 75% rate seen in the SHOCK trial.3 This may be due to different definitions of cardiogenic shock used in various registries and randomized trials.1–4/SUP> The clinical definition of cardiogenic shock used in this study is similar to that used in other multicenter registry studies.1,4 The 46% mortality rate for elderly patients with cardiogenic shock seen among these selected PCI patients is significantly lower than the 69% mortality rate seen in the unselected Worcester Heart Attack Study’s elderly shock cohort.4 Notably, this study analyzed unselected shock patients hospitalized in the mid-1990s; thus, both patient selection and changes in interventional procedures occurring later in the 1990s may in part explain the lower mortality rate seen in this more current cohort. Another explanation for the markedly lower mortality rate seen in this decade-long registry experience is the general improvement in shock mortality seen after the SHOCK trial completed enrollment (Figure 2).12 However, it is equally important that discrepancies between registry outcomes and randomized clinical trials with respect to PCI mortality rates may be expected with respect to high-risk patient subgroups. An example of this discrepancy is the outcome of diabetic patients in the BARI trial as compared to the BARI registry. In the BARI registry, the 5-year mortality rate for diabetic patients undergoing multivessel PCI was 14.4%, as compared to 34.5% for diabetic multivessel PCI patients in the randomized trial.13 This much lower than expected mortality rate in the registry group reflects clinical judgement that was applied to appropriate selection of diabetic patients for multivessel PCI (i.e., more focal multivessel coronary artery disease among diabetic registry patients as opposed to randomized trial patients).9,14 Similarly, our registry defines a much lower mortality rate than the SHOCK trial for clinically selected elderly patients with PCI for cardiogenic shock. Understanding the details of “good clinical judgement” that lead to these improved real world outcomes for high-risk patients may be the key to further improving outcomes for this highest risk subgroup of AMI patients. Selection of elderly shock patients for PCI. The importance of selecting elderly shock patients for possible PCI is underscored by the frequency of this clinical scenario; nearly 40% of patients with AMI complicated by shock will be >= 75 years old.12 Selection of elderly patients with a favorable lack of comorbidities would not have been possible under the restrictions imposed by a randomized clinical trial such as the SHOCK trial. Factors that have been associated with increased mortality among elderly patients undergoing PCI include a history of renal failure, diabetes mellitus, prior revascularization and peripheral vascular disease.15,16 These and other adverse clinical variables would be expected to have an increased prevalence in elderly versus non-elderly patients undergoing PCI for shock.17–19 The similar prevalence of significant comorbidities among elderly versus non-elderly shock patients undergoing PCI in the Northern New England Cardiovascular Study Group Registry suggests that cardiologists were able to select elderly shock patients for PCI who clinically “looked younger than their stated age” (Table 1). For example, the prevalence of peripheral vascular disease and renal failure should be higher in elderly as compared to non-elderly patients undergoing PCI.17 The similar prevalence of these comorbidities among the older shock cohort selected for PCI suggests that operators were carefully selecting older shock patients without the usual increased prevalence of comorbid conditions expected in that age group. Of particular importance, the prevalence of diabetes mellitus was similar in both the young and old patients undergoing PCI for cardiogenic shock. Recently, diabetes mellitus has been shown to be an independent predictor of hospital mortality for shock patients treated during the stent era in the Global Registry of Acute Coronary Events (GRACE);12 our multivariate model confirms the negative impact of this particular comorbidity on hospital survival for these patients. The elderly shock patients selected for PCI also had similar angiographic and procedural complexity. The prevalence of Type B2/C lesions was not higher among elderly as compared to non-elderly shock patients undergoing PCI, as would be expected based upon prior analyses of elderly patients in stent trials.19 This translated into a similar ability to achieve stent placement in elderly and non-elderly groups (approximately 70%) undergoing PCI for shock during the stent era (1997–2000). Recent data from single and multicenter registries have suggested that stent placement is among the most powerful independent predictors of hospital survival among patients undergoing revascularization for cardiogenic shock.12,20 Our multivariate analysis confirms the independent importance of having a “stentable” patient and lesion for favorable outcomes in this high-risk patient group. Thus, clinical selection of elderly shock patients for PCI appears to have been performed according to two criteria: 1) a similar clinical comorbidity profile to that expected for a younger patient with AMI complicated by shock; and 2) an ability to use the full armamentarium of current PCI technology (including intraaortic balloon placement, GP IIb/IIIa inhibition and, most importantly, coronary stenting) based upon similar angiographic, peripheral vascular and bleeding profiles for the elderly and non-elderly shock PCI patients. Study limitations. First, this registry represents our regional experience and is generalizable only to the extent that our patterns of practice and outcomes are similar to those in other communities. Second, we cannot comment on whether percutaneous revascularization was the best treatment strategy for elderly patients as we do not know the characteristics and outcomes of those patients who were managed medically. Given the difficulty in performing randomized clinical trials in these high-risk elderly patients, multicenter registry studies may be the best way to assess current outcomes and associations with improving hospital survival. Third, it is recognized that the overall sample size of elderly shock patients undergoing PCI in this study is not large (n = 75). Still, this is the largest report of outcomes for elderly shock patients undergoing PCI to date and thus may best reflect current outcomes. While our study points to a negative interaction with diabetes mellitus and shock outcomes, the conclusive definition of other key variables for selecting elderly shock patients for PCI would require a much larger sample than obtained in this multicenter registry cohort. Conclusion. Despite the results of the SHOCK trial, it appears that there is a group of identifiable elderly patients who can be treated with percutaneous revascularization with an acceptable risk. These are the older patients with comorbidities and anatomy more similar than not to their younger counterparts. Further identification of variables that define elderly patients with shock who should be candidates for PCI may have important implications for improving outcomes in this high-risk group of patients. Acknowledgment. We are indebted to participating hospitals in the Northern New England Cardiovascular Study Group for their cooperation.1. Goldberg RJ, Samad NA, Yarzebski J, et al. Temporal trends in cardiogenic shock complicating acute myocardial infarction. N Engl J Med 1999;340:1162‚Äì1168.
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