Coronary care units (CCUs) were first established in the late 1960s to improve mortality after acute myocardial infarction by detecting and aggressively treating arrhythmias while providing a clinical laboratory for advancing research and treatment of acute coronary syndromes 1. The CCU became widely utilized after Killip and Kimbal 2 reported a nearly 20% reduction in mortality with its use. Since that time, these units have evolved into the modern-day CCUs, which now have expanded roles and allow advanced monitoring and treatment modalities for the management of not only acute coronary syndromes (myocardial infarction and unstable angina), but also advanced heart failure, complex dysrhythmias, pulmonary hypertension, and myocarditis. They also as serve as a platform for research and trial of advanced therapeutic techniques.
In the early 1990s, Tesky et al. 3 reported a 13% mortality for patients admitted to the CCU in Ottawa, Canada. Rotstein et al. 4 reported a crude 30-day mortality rate of 5.4% for a hospital in Israel in the mid-1990s, which was slightly lower than the 7–8% CCU mortality rate in the United States from 1989 to 2006 reported by Katz et al. 5. In the present era of quality improvement and benchmarking, other than the data from Katz et al. 5, it is surprising to find that there are limited data available on mortality or predictors of survival for patients admitted to the CCU. Without a standard for comparison, it is difficult to evaluate hospital and physician performance and to find areas of improvement for patients admitted to these specialized and costly units.
Accordingly, the goal of the present study was to provide additional data on mortality in the modern-day CCU by sampling hospitals in a large urban setting. The study also aimed to define clinical, demographic, temporal, treatment, and logistic factors of patients surviving and succumbing in the CCU and to better understand mortality in the CCU in the hope of improving the standard of care of patients admitted to these units.
We attempted to obtain data from 29 hospitals in the New York City metropolitan area for the 2011 calendar year. Six hospitals were willing to share their data including the number of admissions and the number of deaths in the CCU over that time period. We only used data from hospitals that had a dedicated CCU [separate from a medical intensive care unit (ICU) or other ICUs]. Each CCU had a dedicated cardiologist who served as the director. The hospitals providing data are listed in the Acknowledgements section. Deaths were only included in the mortality data if the patient died in the CCU, not if the patient was discharged to another hospital unit and succumbed there.
As the range of mortality data was quite narrow and the information identified as particularly important to CCU mortality was comprehensive, patient information including demographics, admission diagnoses, previous medical history, laboratory data, treatment during CCU stay, and time and cause of death was tabulated from nearly 1000 patients from two representative hospitals and compared with that from patients who survived to CCU discharge. All data were deidentified after collection. The study was approved by the Institutional Review Board of Beth Israel Medical Center.
All differences between survivors and nonsurvivors in terms of demographic measures, prior medical history, and primary diagnosis were evaluated using t-tests for mean differences in the case of normally distributed variables or t-tests for proportions for measures that reflected proportions. All analyses were carried out using Stata, version 12.2 (Stata Corp. LP, College Station, Texas, USA).
Of the six hospitals providing data, all had dedicated cardiac care units. All hospitals were teaching hospitals with house staff in both Internal Medicine and Cardiology ACGME-approved training programs. There were a total of 4958 hospital beds in the six hospitals providing data. The average number of CCU beds was 11 per hospital (range 8–16). The average ratio of total hospital beds to CCU beds was 73 (range 38–152). There were 4275 admissions to the CCUs of the six hospitals in 2011. There were a total of 239 deaths. As shown in Fig. 1, the weighted average mortality in the CCU across all hospitals was 5.6%, with a range from 2.2 to 9.2%.
The demographic characteristics of the 956 patients admitted to the CCU of the two representative hospitals are summarized in Table 1. The average age of the patients admitted to the CCU was 67 years, with 68% being male. The breakdown of admissions to the CCU by race mirrors admissions to urban New York City metropolitan hospitals. Asians had a slightly higher mortality rate (9.7%) compared with other races (African-Americans, 5.8%; Hispanics, 8.2%; Whites, 6.3%); however, this was of borderline statistical significance (P=0.055).
Most patients (33%) admitted to the CCU had a history of diabetes (Table 2). Nearly 32% had a history of coronary artery disease. Approximately 20% were active smokers. On evaluating mortality based on prior medical history, death was found to be more common among patients with a history of systolic heart failure, atrial fibrillation, cerebral vascular accident or transient ischemic attack, metastatic cancer, or cirrhosis (Table 2).
The most frequent causes for admission to the CCU were ST-segment elevation myocardial infarction, non-ST-segment elevation myocardial infarction, and unstable angina (Table 3). Acute coronary syndromes accounted for nearly 57% of all CCU admissions. Less frequent were admissions for systolic heart failure (6.2%), bradycardia (5.6%), cardiac arrest (4.6%), and atrial fibrillation (3.6%). Approximately 8% of patients were admitted to the CCU for ‘other’ reasons, which included monitoring after coronary intervention, aspirin desensitization, gastrointestinal bleeding, seizures, drug overdoses, or severe electrolyte abnormalities. Survival was worse among patients admitted after cardiac arrest (mortality of 25.0%), those with sepsis (21.7%), those with primary respiratory failure (16.7%), and those with systolic heart failure (15.3%); P less than 0.05 for each of these diagnoses.
In terms of clinical signs and laboratory evaluation at the time of CCU admission, patients admitted with hypotension, tachycardia, diminished oxygen saturation on pulse oximetry, hypocapnia, elevated blood urea nitrogen, glucose, magnesium, liver enzyme, troponin, or B-type natriuretic peptide levels, or an elevated international normalized ratio, had higher rates of mortality (Table 4).
Of all patients admitted to the CCU, 37% underwent cardiac catheterization and/or percutaneous coronary intervention during their CCU stay, 15% received treatment with either inotropic agents or pressors, 11% were placed on mechanical ventilation, 9% received an intra-aortic balloon pump for cardiac support, and ∼6% were on respiratory assistance with bilevel positive airway pressure.
Looking at mortality excluding patients who were made ‘do not resuscitate’ during their CCU stay, those who experienced in-CCU cardiac arrest requiring defibrillation, those requiring right heart invasive monitoring (reflecting more advanced heart failure), those on mechanical ventilation, those receiving inotropic or pressor therapy, those requiring emergent dialysis, and those with invasive cardiac support with an intra-aortic balloon pump had higher rates of in-CCU mortality (Table 5). The most frequent causes of death were intractable cardiogenic shock, brain death, respiratory failure, multiorgan failure, and hypotension (Table 6).
In terms of the time of death, there was no difference between day and night or in the day of the week. The average length of hospital stay for nonsurvivors was 5.7 days (SD=9.1 days; range <24 h to 56 days), with 28.8% of them dying within 24 h of admission. The average length of hospital stay for survivors was 3.4 days (SD=3.4 days, range <24 h to 32 days).
To our knowledge, this is the first study to define CCU mortality in multiple urban hospitals in the current practice era. Overall, mortality for patients admitted to the CCU was 5.6%. The mortality rate was found to be relatively uniform across the New York City metropolitan hospitals that provided data.
The mortality observed and reported here is significantly lower than that reported by the Myocardial Infarction Research Units in the 1960s, which was in the range of 25–35% 1. Certainly, advances in revascularization therapy, arrhythmia detection and treatment, and pharmacotherapy have contributed to the survival increase. In addition to overall mortality decreases, the mortality from acute myocardial infarction has also steadily decreased from about 20–25% in the 1980s to 10–15% in the 1990s to ∼6% at present 1,6. However, it should be noted that there have been substantial changes in diagnosis at admission to the CCU over the years. Katz et al. 5 reported an increased prevalence of critical noncardiovascular diagnoses including sepsis, acute renal failure, and respiratory failure. Therefore, it must be recognized that the mortality figures noted in the present study are also inclusive of many other diagnoses that were not seen in early Myocardial Infarction Research Units, which likely influence patient outcome. Further, the earlier mortality data were certainly from before the era of thrombolytic therapy and 24-h cardiac intervention. Thus, it is impossible to compare current mortality with those collected from CCUs previously.
In 1991, Teskey et al. 3 reported an inhospital mortality rate of 13% in their CCU and showed that the Acute Physiology and Chronic Health Evaluation (APACHE) II scoring system worked reasonably well in predicting mortality, although the receiver operating characteristic curve was relatively flat. The mean length of stay in their CCU was 2.9 days. Similar to our findings, patients with out-of-hospital cardiac arrest had a very high mortality. In an important longitudinal study, Katz et al. 5 reported a CCU mortality rate of 7–8% in the Duke University Hospital and found it to be relatively stable over the time period from 1989 to 2006 despite the increasing acuity of illness. A recent study of 684 patients at the Heart Centre of the Cologne University Hospital, Germany, reported a mortality rate of 32.5%, which is much higher than that reported here. The high rate was attributed to the center having an intermediate unit for less severely ill patients 7. Using data obtained from over 1700 hospitals in the United States, Groeger et al. 8 showed that the average hospital had nine CCU beds and ∼50% of CCU admissions were for ischemic heart disease. In addition, in this survey, ∼20% of patients in the CCU received invasive arterial monitoring and ventilator support. Fourteen percent received right heart catheterization, and 27% received inotropic support. These findings are in aggregate similar to our data presented here. Similarly, Rotstein et al. 4 reported that the average age of patients admitted to the CCU was 63 years, with 73% being male, in a single center in Israel. Sixty-one percent of their patients underwent cardiac catheterization, and mortality was 5.4%, which is nearly identical to our aggregate average.
In contrast to the limited data for CCUs, admission and mortality data for medical or surgical ICUs have been extensively reported. Mortality rates in the ICU have been reported to range from 5 to 27% 9–11. A 1993 study collected data on 32 850 ICU beds, with 25 871 patients from 2876 separate ICUs in 1706 hospitals in the United States 8. In these ICUs, the three primary admitting diagnoses were ischemic heart disease, postoperative management, and respiratory insufficiency/failure, which differed from the primarily cardiac diagnosis of the patients admitted to the CCU in this study. Another report from the Mayo Clinic evaluated 46 381 patients admitted to the ICU from 1994 to 2003 and included 13 755 (29.7%) patients who had a cardiovascular diagnosis. ICU mortality was 5.3% overall, with mortality in the medical ICUs being 9.7%, multispecialty ICUs being 7.8%, and surgical ICUs being 2.7% 9.
Over the last decade, specific efforts have been made to improve the quality of medical care in the ICUs in the USA. Because mortality is significantly affected by patient demographics, comorbidities, and severity of illness, risk-prediction models have been developed to adjust for these factors 12–15. The three most widely used models have been updated over the past few years: the mortality probability model III 16; the simplified acute physiology score III 17; and APACHE IV 18. These models differ substantively in the number and type of variables used to assess mortality risk. Prior studies have compared older versions of these models 19–23. However, the predictive accuracies of these updated models have not been directly compared. In addition, there exists substantial variation in ICU risk-adjusted mortality rates. This variation in outcome may represent true differences in performance or merely the inability of the risk-adjustment models to account for unmeasured differences in case mix. Although there is no ‘gold standard’ against which to judge available models, a scoring system would be an ideal way to measure CCU performance.
A recent statement from the American Heart Association 24 emphasizes the complex changes in the environment of the present-day CCU and recognizes that further modifications in the structure and training methods may be necessary in the future. With the rising cost of medical care in the ICUs in the USA to over $55 billion in 2000 25, it is important that benchmarks and scoring systems for the CCU be developed to provide the most efficient care for patients.
Several important limitations of this study reduce the generalizability of the results presented here. First, the data are from a relatively small number of New York-based hospitals. Many hospitals were unwilling to share their data with us. Nonetheless, these data represent a reasonable cross-sampling of hospitals on CCU mortality with a fairly narrow range of mortality, suggesting that the overall mortality in the CCU is somewhere between 5–8%. Second, detailed information on demographics, diagnosis, treatment, and mortality was only obtained from two hospitals because of the inability to obtain full information from the remaining four hospitals. However, these two centers had mortality rates that fell between the rather narrow range of CCU mortality rates reported here and included a reasonable number of patients; thus, they are believed to represent the practice of the current-day, state-of-the-art CCU. However, these data should be used only as a starting point for comparison. Although we recognize that these limitations are significant, we believe the data represent a comparison point that can be used for intrahospital comparison, prediction, and quality improvement.
In this study of urban New York City hospitals, the average mortality rate is 5.6%. The major admitting diagnosis to the CCU was acute coronary syndrome. Asians appear to have increased rates of death compared with other races. In-CCU cardiac arrest, receiving a pulmonary artery catheter, requiring emergent hemodialysis or inotropic/pressor support, being placed on a ventilator, and receiving an intra-aortic balloon pump were all associated with a mortality rate of greater than 10%. Approximately 29% of those who died in the CCU died within 24 h. Those patients who survived had an average length of stay of 3.4 days. The data presented should serve as a platform for further research and quality improvement in the CCU setting and, if corroborated in larger samples, the development of a CCU mortality scoring system.
The authors thank the following CCU Directors for their participation in this study: Dr Linda Cuomo, Westchester Medical Center, Valhalla, NY; Dr Michael Kim, Mount Sinai Hospital, Manhattan, NY; Dr Mark Menegus, Montefiore Medical Center, Bronx, NY; Dr Eyal Herzog, St. Luke’s and Roosevelt Hospitals, Manhattan, NY. They also acknowledge the dedicated care of the nurses, associated healthcare staff, house officers, and fellows who care for patients in the CCU.
Conflicts of interest
There are no conflicts of interest.
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Keywords:© 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
cardiovascular mortality; coronary care unit; prognosis