Gradual Decline in the Age-Adjusted In-Hospital Mortality Rate From STEMI-Related Cardiogenic Shock Irrespective of Cause, Race or Gender With Persistent Higher Mortality Rates in Women Despite Multivariate Adjustment

Abstract: Background. Recent improvements in the care of critically ill patients with cardiogenic shock (CS) should be associated with improved outcomes. The goal of this study was to evaluate the trends of age-adjusted mortality rates for all-cause and ST-elevation myocardial infarction (STEMI)-related CS in the United States. Methods. The Nationwide Inpatient Sample (NIS) database was utilized to calculate the age-adjusted mortality rate of all-cause and STEMI-related CS from 1996 to 2006. We used specific ICD-9 codes for CS and STEMI based on race and gender. Results. We found a gradual decrease in mortality over the 10-year period in patients suffering from all causes or STEMI-related CS irrespective of gender and race with a persistently higher mortality rates in women and African Americans. However, after multivariate adjustment, only female gender remains associated with persistently higher mortality. The age-adjusted mortality rate from STEMI-related CS in women was 2.2% in 1996, with a gradual reduction to the lowest level of 1.7% in 2006 (P<.01). Likewise, the age-adjusted mortality rate from STEMI-related CS in men was 1.7% in 1996, which declined to the lowest level of 1.4% in 2006 (P<.01). Conclusion. Regardless of gender and race, age-adjusted in-hospital mortality is gradually declining in patients presenting with all causes or STEMI-related CS. However, as compared to men, women suffer from persistently higher mortality rates in the setting of STEMI-related CS despite multivariate adjustment. 

J INVASIVE CARDIOL 2014;26(1):7-12

Key words: epidemiology, cardiovascular disease, coronary artery disease incidence, acute myocardial infarction, acute coronary syndrome, ST-elevation myocardial infarction, shock, cardiogenic shock

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Despite a decline in ST-elevation myocardial infarction (STEMI) and non-STEMI related mortality,^1-3 cardiogenic shock (CS) has remained a leading cause of death in patients hospitalized with acute myocardial infarction (AMI).⁴ STEMI leading to left ventricular pump failure accounts for more than 75% of CS cases.⁵ The remaining cases are secondary to infarction-related mechanical complications like papillary muscle or interventricular septum rupture. Data suggest that CS complicates about 5%-8% of STEMI and 2.5% of non-STEMI cases.^6-8 Overall, in-hospital mortality in patients with CS associated with STEMI remains high.^7,9,10 

Following the findings of the 1999 SHOCK trial,⁵ which showed improved survival of patients with CS in the setting of STEMI who were assigned to early mechanical revascularization rather than medical management, the American College of Cardiology (ACC) and American Heart Association (AHA) guidelines strongly recommended early mechanical revascularization as a preferred therapy in such cases.¹¹ No changes were made to this approach in the subsequent (2005 and 2007) ACC/AHA updated guidelines. Furthermore, over the last two decades, accumulating evidence suggests that early reperfusion, irrespective of revascularization method, results in better survival and reduced complications in patients with STEMI. Based on these observations, ACC/AHA guidelines recommend a door-to-needle time of less than 60 minutes in patients with STEMI who present within 3 hours of symptom onset or a door-to-balloon time of less than 90 minutes within 12 hours of symptom onset.¹² 

These guidelines were established to improve survival and decrease the risk of complications in patients with STEMI and CS. However, little is known about the practical implementation and the real-world benefits of these recommendations. As we know from previous studies,^13,14 development of guidelines does not always result in broad implementation. With early reperfusion of occluded arteries in patients with CS in the setting of STEMI, one would expect to see a reduction in overall mortality; however, it is not known whether the execution of these guidelines has resulted in improvement in patient outcome in the real world. To see whether the implementation of new evidence-based guidelines resulted in better survival in patients with STEMI-related CS, we retrospectively analyzed a large database. Our hypothesis is that the recent improvements in the care of STEMI patients should lead to a reduction in the in-hospital mortality from CS, irrespective of gender or ethnicity. 

Methods

Data collection and data sources. The Nationwide Inpatient Sample (NIS) is a set of hospital inpatient databases obtained by the Healthcare Cost and Utilization Project (HCUP). This database was created by the Agency for Healthcare Research and Quality (AHRQ) using a Federal-State-Industry partnership. HCUP Researchers use NIS databases to identify and analyze national trends in health-care utilization, patient outcomes, and the quality of care. The NIS is the largest all-payer inpatient care database in the United States; containing over 8 million hospital stays each year. Using the available NIS database from the years 1996 to 2006, we analyzed the trends over time and explored what was most common during that period. The NIS contains information on all patients regardless of how treatment is reimbursed, including persons covered by Medicare, Medicaid, or private insurance companies. It also contains an approximately 20% stratified sample of patients from all community hospitals in the United States, with primary and secondary diagnoses, primary and secondary procedures, demographics, and admission and discharge statuses. Furthermore, the NIS contains safeguards to protect the privacy of individual patients, physicians, and hospitals. 

Description of the data. For this study, we utilized the International Classification of Diseases, ninth revision, Clinical Modification (ICD-9-CM) primary code for cardiogenic shock (785.51). Furthermore, regarding STEMI-related CS, we utilized ICD-9 codes that were consistent with STEMI in the NIS database. In order to reduce the number of patients with non-atherosclerotic causes of cardiogenic shock and STEMI, we studied patients over the age of 40. The following codes were found to be consistent with the diagnosis of STEMI: true posterior wall infarction (410.61), AMI of the anterolateral wall (410.01), infarction of other anterior wall (410.11), infarction of inferolateral wall (410.21), infarction of inferoposterior wall (410.31), other inferior wall (410.41), lateral wall (410.51) infarctions. Also, various specified sites including infarction of atrium, papillary muscle, septum alone, or STEMI in other specified sites (410.81) were present. In addition, we obtained the demographic information, such as age and gender, so we could calculate the age-adjusted occurrence of STEMI patients per 100,000 patients, which were plotted from the years 1996-2006. Furthermore, we calculated the total number of STEMI-related mortality cases over the years studied. 

Statistical analysis. The average age-adjusted mortality rates from STEMI-related and all-cause CS were calculated by multiplying age-specific mortality rates with age-specific weights. The age-specific weights used were obtained from the year 2000 data, approximating the United States population age brackets. The weighted rates were summed across age groups to give the age-adjusted rate for each year from 1996 to 2006. The independent samples t-test was used for analysis. The Statistical Package for Social Sciences (SPSS) software was used for computations. We used stepwise multiple regression analysis for multivariate adjustment. A P-value of <.05 was considered statistically significant.

Results

The study population consisted of 49,826,834 hospital admission samples in the NIS database from 1996 to 2006. STEMI-related cardiogenic shock patients had the following demographics: total number, 47,511; mean age, 69.67 ± 12 years; gender, 56.9% male and 43.1% female; and race, 62.5% Caucasian, 3.9% African-American, 4.6% Hispanic. A summary of our patients’ baseline demographics can be seen in Table 1.

We found a gradual decrease in mortality over the 10-year study period in patients suffering from all-cause or STEMI-related CS irrespective of gender or race, with a persistently higher mortality rate in women and African-Americans (Figures 1 and 2). However, after multivariate adjustment, this association between higher mortality and STEMI-related CS remained significant only for women. The age-adjusted mortality rate from STEMI-related CS in women was 2274 per 100,000 in 1996, with a gradual decline to the lowest level of 1724 per 100,000 in 2006 (P<.01). This decline was similar in males (from 1.7% in 1996 to 1.4% in 2006) and in females (from 2.2% per 100,000 in 1996 to 1.7% per 100,000 in 2006; Figure 1). Regarding ethnicities and gender (Figure 3), there were persistently higher mortality rates in women and African-Americans, with the lowest mortality rate seen in Caucasians (Figures 3 and 4). 

The total unadjusted in-hospital mortality rate from all causes of CS has remained steady over the years, irrespective of gender or race (Figures 5 and 6). There was a notable decline in the total mortality of patients with STEMI-related CS throughout gender and ethnicities (Figures 7 and 8). However, after multivariate adjustment for hyperlipidemia, chronic renal failure, type-2 diabetes, pulmonary hypertension, heart failure, smoking, and a history of coronary disease, only female gender remained independently associated with higher mortality in patients with STEMI-related CS (female gender odds ratio [OR], 1.4; 95% confidence interval [CI], 1.2-1.6; P<.001 for year 1996 and OR, 1.3; 95% CI, 1.1-1.5; P=.01 for year 2006). After multivariate adjustment, African-American race was not found to be independently associated with higher mortality. 

Discussion

Our results indicated that, irrespective of gender or ethnicity, age-adjusted mortality for all-cause and STEMI-related CS gradually decreased over the 10 years of the study period, with persistently higher mortality rates in women and African-Americans. Furthermore, we observed significant reductions in the unadjusted total mortality rate from STEMI-related CS irrespective of gender and ethnicities, but not all causes of CS. 

CS following AMI is a devastating condition which, despite considerable improvements in the medical management, still carries a very high mortality. Clinical predictors of CS in the setting of STEMI after PCI include advanced age, diabetes mellitus, anterior wall MI, previous MIs, multivessel disease, and prior heart failure,^15,16 and coexistent chronic total occlusion (CTO) of the non-infarct related artery (IRA).¹⁷ Pathological studies have shown that the risk of CS development is higher when >40% of left ventricular mass has been affected by infarctions.¹⁸ Similarly, factors associated with adverse outcomes in patients with CS include advanced age, female sex, presence of altered sensorium, cold clammy extremities, or oliguria;¹⁹ left ventricular ejection fraction <28% or severe mitral regurgitation;²⁰ location of culprit lesion in left main or saphenous vein graft;²¹ postprocedural TIMI flow grades 0-2 in the IRA;²² and right ventricular dysfunction.²³ On the other hand, regardless of the method of revascularization (fibrinolytics or mechanical), an open IRA in patients with CS following AMI correlates strongly with better survival.²⁴ However, the SHOCK (Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock) trial later confirmed the superiority of early mechanical revascularization (PCI or emergency coronary artery bypass graft surgery) to medical management followed by late or no revascularization in patients with CS in the setting of AMI. Patients with CS in the setting of STEMI who were treated with early mechanical revascularization had lower 6-12 month mortality than those assigned to medical management.^5,25 

Early reperfusion with either fibrinolytics or mechanical revascularization has been proven to be associated with better survival and decreased AMI-related complications in patients presenting with STEMI. With fibrinolytic therapy, the benefit is greatest when these agents are given within 2 hours of symptom onset.²⁶ Similarly, primary PCI within 2 hours of symptom onset and a door-to-balloon time of <90 minutes has been shown to improve mortality in patients with STEMI according to several studies.^27-29 

Additionally, primary PCI, when compared to fibrinolysis, is likely to result in more effective ST resolution and better IRA patency and reduced infarct size.³⁰ Intuitively speaking, these PCI-related benefits should result in better outcomes, ie, reduced incidence and mortality with CS in STEMI patients treated with PCI; however, the actual data comparing PCI to thrombolytics in preventing CS are sparse. Recently, Lindholm et al³¹ compared fibrinolysis to PCI as a preferred strategy to prevent CS in patients with STEMI and found that angioplasty does not offer additional protection against in-hospital development of CS in STEMI patients. These findings indicate that it is not the shift from thrombolytics to PCI, but rather the early revascularization and the improvements in pharmacological management of patients with STEMI, that is driving the incidence of CS to a lower level.

Similarly, better survival in patients with STEMI complicated by CS can be explained by improvements in medical management and implications of evidence-based guidelines for the management of CS. After the findings of the SHOCK trial, which confirmed a 13% absolute increase in the 1-year survival of patients assigned to early mechanical revascularization, this strategy has been widely adopted by many clinicians, resulting in improved CS-related mortality. This was shown by Babaev et al,⁶ who studied 293,633 subjects in the NRMI database over a period of 10 years (1995 to 2004). The authors found that the overall in-hospital mortality due to STEMI-related CS decreased from 60.3% in 1995 to 47.9% in 2004 (P<.001). It paralleled the increased rates of primary PCI for STEMI-complicated CS from 27.4% to 54.4%. The authors found a reduction in the rates of thrombolytic therapy (19.9 to 5.6%), with no change in the use of intraaortic balloon pump in this setting. They also found that the door-to-balloon time for primary PCI in patients with CS decreased from 117 minutes to 103 minutes over the study period. These findings of improved mortality in STEMI-related CS cases shown by us and the above-mentioned study indirectly confirms the benefit of early mechanical revascularization. In addition, there is now a growing consensus that the earlier the revascularization (lytics or mechanical) in patients with CS, the better the resulting outcome. In the SHOCK trial, there appeared to be increasing mortality as the time to revascularization increased from 0 to 8 hours. Also, the increasing use of stenting and glycoprotein IIb/IIIa inhibitors was shown to be independently associated with improved outcomes in patients undergoing PCI for STEMI-related CS.³² Systemic inflammation^33-35 and metabolic derangement^36,37 are other contributing factors leading to higher mortality of patients with CS. 

Finally, we confirmed previous studies on the racial and gender-based outcomes, the disparity between men and women, and between Caucasians and African-Americans.^1,38 However, the African-American race was not independently associated with mortality after multivariate adjustment, but the female gender continued to be independently associated with mortality. There are many explanations in the literature trying to explain this disparity. The most plausible explanation is based on comorbidities. It states that women and African-Americans presenting with cardiovascular disease at the same age appear to have a higher number of comorbidities.³⁹ However, despite adjustments made for those comorbidities, the female gender has remained independently associated with higher mortality when presenting with STEMI, which is consistent with other studies.⁴⁰ In one study, African-Americans had a lower rate of cardiac catheterization⁴¹ when presenting with myocardial infarction and a longer delay to reperfusion therapy.⁴² Racial and gender disparity remain a major public health controversy and is beyond the scope of this manuscript. Randomized clinical trials are warranted to evaluate gender or race-specific factors in regard to mortality in patients presenting with STEMI.

Study limitations. We used an administrative database using ICD-9 codes, which has some limitations in accuracy, limiting our data. This could explain lower total mortality in our patients with CS than expected due to possible over-diagnosis of this condition during coding. Furthermore, our study was a retrospective data analysis and not a randomized trial, limiting our results.

Conclusion

Age-adjusted in-hospital mortality has been gradually declining in patients present with all causes of STEMI-related CS, regardless of gender or race. However, women have persistently higher mortality rates over the years studied despite multivariate adjustment, which needs further confirmation. Total mortality from CS only declined in STEMI-related CS, irrespective of gender or race and not in all causes of CS. This evidence suggests that the advancements in percutaneous treatment of patients diagnosed with STEMI and cardiogenic shock have led to improved outcomes. Furthermore, women and African-Americans had persistently higher mortality rates. However, after multivariate adjustment, only female gender remained independently associated with CS-related mortality. Our findings are consistent with previous studies showing a large gap in the outcomes between men and women and possibly between African-Americans and Caucasians in the cardiovascular outcomes.

Acknowledgment. We would like to thank Stephen Alavi for editing this manuscript.

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From the ¹CareMore Health Care Arizona, ²Division of Cardiology, The Southern Arizona VA Health Care System, Tucson, Arizona; ³Division of Cardiology, University of Arizona Sarver Heart Center, Tucson, Arizona; and ⁴Department of Medicine, Long Beach VA Medical Center, Long Beach, California.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted June 17, 2013, provisional acceptance given July 10, 2013, final version accepted September 13, 2013.

Address for correspondence: M. Reza Movahed, MD, PhD, FACP, FACC, PSCAI,  Arizona CareMore Regional Cardiology Director, Professor of Medicine, University of Arizona Sarver Heart Center, 7091 E. Speedway Blvd., Tucson, AZ 85710. Email: rmova@aol.com