ONLINE APPENDIX
Statistical Methodology
We have used hierarchical modeling to adjust for the clustered nature of cases in the Nationwide
Inpatient Sample. We used a unique hospital identifier to group together cases from the same
hospital. Year of hospital stay was included as an independent variable in both regression
analyses to control for confounding by patient and hospital differences across time that are not
captured in other variables.
Tests for linear and curvilinear trends in disease characteristics and outcomes over time were
performed using variance-weighted regressions. This technique has been described previously
and is among the methods recommended by the Healthcare Cost and Utilization Project (HCUP)
for use with the Nationwide Inpatient Sample.1,2 Estimates and their associated standard errors
are generated for each year using methods appropriate for complex sample surveys, taking into
account clustering, case weighting, and the stratification strategy. Variance-weighted regression
analyses are then performed using the summary datasets generated. This methodology takes into
account the standard errors associated with the estimates of each year but does not assume
homogeneity of variance. In accordance with HCUP guidelines, we defined the threshold for
including estimates in trend analyses to be a relative standard error less than 30%.
Because of the difficulties inherent in presenting yearly estimates of many different
characteristics and outcomes over an 8-year period, we opted to aggregate the data into 2 groups
1
Bao Y, Sturm R. How do trends for behavioral health inpatient care differ from medical inpatient care in US community
hospitals? J Mental Health Policy Econ 2001;4:55-63.
2
Using the Nationwide Inpatient Sample to Estimate Trends. Rockville, MD: Healthcare Cost and Utilization Project
(HCUP), Agency for Healthcare Research and Quality, 2011. (http://www.hcup-us.ahrq.gov/toolssoftware/ccs/ccs.jsp).
2
of years: 2004 to 2007 and 2008 to 2011. In Tables 1 to 3, the columns entitled 2004 to 2007 and
2008 to 2011 contain estimates of the weighted means for the characteristics listed. These
weighted means are only for illustrative purposes, designed to help readers interpret the trend
across many years. The actual trend analysis was performed using discrete data for each year
from 2004 through 2011.
3
Online Table 1 Outcomes of Cardiogenic Shock by Indication for Hospital Stay (2008 - 2011)
Characteristics
AMI
CAD
CHF
Other
8.6
5.2
33.5
11.8
9 (3 - 20)
8 (4 - 16)
27 (12 - 46)
16 (6 - 42)
Routine
27.8
26.6
27.9
32.4
Home health care
15.6
21.4
29.0
23.2
Transfer*
56.6
52.0
43.1
44.4
Mortality rate, %
41.2
47.2
32.5
49.2
Permanent device, %
Length of stay, median (IQR),
days
Disposition, %
AMI = acute myocardial infarction; CAD = coronary atherosclerosis and other heart disease; CHF =
congestive heart failure; IQR = interquartile range.
*
Includes short-term hospital, skilled nursing facility, or intermediate care.
4
Online Table 2 Comparison of Case Mix and Frequency for Surgical and Percutaneous MCS
2004 - 2007
Characteristics, n (%)
2008 - 2011
Surgical
Percutaneous
Surgical
Percutaneous
1,895
490
2,882
6,620
(79.5)
(20.5)
(30.3)
(69.7)
Cardiogenic shock
1,029
207
1,911
2,785
present
(83.3)
(16.7)
(40.7)
(59.3)
606
158
902
2,690
(79.3)
(20.7)
(25.1)
(74.9)
384
94
273
1,838
(80.3)
(19.7)
(12.9)
(87.1)
197
87
591
777
(69.4)
(30.6)
(43.2)
(56.8)
485
112
875
1,095
(81.2)
(18.8)
(44.4)
(55.6)
Procedures
Primary diagnosis
AMI
CAD
CHF
Other
MCS = mechanical circulatory support; other abbreviations as in eTable 1.
5
Online Table 3 Outcomes of Surgical and Percutaneous MCS Over Time
Surgical
Characteristics, n (%)
Mortality
Permanent device
Cost of stay
Percutaneous
2004-2007 2008-2011 2004-2007 2008-2011
868
1,364
109
1,806
(45.9)
(47.3)
(22.2)
(27.3)
93
531
*
305
(4.9)
(18.4)
$126,761
$143,131
$90,987
$61,254
30.0
38.8
18.1
12.5
(48.6)
(34.8)
(16.4)
(14.8)
16.3
21.1
15.8
11.9
(28.9)
(33.4)
(22.5)
(21.0)
(4.6)
Length of stay, mean (SD), days
Survivors
Nonsurvivors
MCS = mechanical circulatory support; SD = standard deviation.
HCUP Data Use Agreement prevents the release of cells of tabulated data with ≤10 observations.
*
6
Online Table 4 Composition of “Other” Miscellaneous Diagnoses
Fraction of All Diagnoses, %
Fraction of “Other,” %
Pericarditis, endocarditis,
and myocarditis;
cardiomyopathy (except that
caused by TB or STD)
4.3
20.4
Cardiac dysrhythmias
3.3
15.9
Complications of device,
implant, or graft
3.1
14.8
Complications of surgical
procedures or medical care
1.5
7.3
Aortic, peripheral, and
visceral artery aneurysms
1.0
5.0
Total
13.3
63.4
Diagnostic Group
STD = sexually transmitted disease; TB = tuberculosis.
7
Online Figure 1 - Classification of acute circulatory support strategies. *IABP is a counterpulsation
device rather than a mechanical support device as it does not contribute directly to cardiac output.