Hospital Volume and 30-day Mortality following Hospitalization

for Acute Myocardial Infarction and Heart Failure

Joseph S. Ross, MD, MHS

Mount Sinai School of Medicine

James J. Peters VA Medical Center

Background

• For numerous surgical conditions and medical procedures, admission to higher volume hospitals has been associated with lower mortality rates.

• Strongest associations for cancer and AAA surgeries, more modest for PCI and CABG and orthopedic surgeries.

Background

• Fewer studies of medical conditions.

• Conceptually: – For surgeries and procedures practice

makes perfect – For medical care less routinization;

organizational structures and processes

Background

• Care for medical conditions is common and costly:– HF is most common admission, 2nd most

expensive for Medicare– AMI is 4th most expensive for Medicare

• Drive to improve health care quality – is volume a marker?

Background

• Two studies focused on AMI treatment.– Farley & Ozminkowski (Medical Care, 1992)

used HCUP data from 1980-87, didn’t adjust for invasive capacity: 10% increase in hospital volume decreased mortality 2.2%.

– Thiemann et al. (NEJM, 1999) used CCP data from 1994-5, prior to key advances, but adjusted for invasive capacity: HR=1.17 (1.09-1.26) [lowest quartile to highest quartile]

• No studies focused on HF treatment.

Research Objective

• To examine whether admission to a higher volume hospital is associated with lower mortality rates for AMI and HF.

Data Source

• Medicare Provider Analysis and Review (MEDPAR) claims data from all FFS beneficiaries hospitalized from 2001-3 in U.S. acute-care hospitals.

Study Population

• FFS patients hospitalized for AMI and HF identified using ICD-9-CM codes.

• Transfers linked into a single episode of care; outcomes attributed to index hospital.

• Excluded patients admitted to hospitals with 10 or fewer admissions, admissions <24hrs not AMA.

Main Outcome Measure

• 30-day risk-standardized all-cause mortality rates (RSMR).

Primary Independent Variable

• Hospitals were categorized by condition-specific volume quartile (prior to application of exclusion criteria):– Low (Q1+Q2)– Moderate (Q3)– High (Q4)

Statistical Analysis

• Weighted hierarchical model that included patient variables (1st level) and hospital variables (2nd level):– CABG surgery/PCI capacity– Teaching status– Ownership status

Results

• From 2001-3:– 801,307 AMI hospitalizations in 3,978 hospitals– 1,245,564 HF hospitalizations in 4,328 hospitals

Mean Condition-Specific Volume

Hospital Volume

Low Moderate High

AMI 41 149 647

HF 100 312 1031

% of Patient Hospitalizations

Hospital Volume

Low Moderate High

AMI 4% 19% 77%

HF 5% 22% 73%

Patient Characteristics by Volume

(For AMI) Hospital Volume

Low Moderate High

Sociodemographics

Age, Mean 81 80 79

Female, % 57 54 51

Past Medical History

Prior MI, % 12 12 14

Valvular heart disease, % 12 13 16

Htn, % 33 36 49

DM, % 25 27 33

PVD, % 15 16 19

Hospital Characteristics by Volume

(For AMI) Hospital Volume

Low Moderate High

CABG surgery capacity, % 2 10 59

PCI capacity, % 3 17 57

COTH member, % 1 3 17

Teaching affiliate, % 6 13 44

Public ownership, % 36 17 9

Volume & Observed AMI Mortality

23.9%

20.9%

17.2%

0%

10%

20%

30%

Low Moderate High

Volume & AMI RSMR

• Admission to both high and moderate volume hospitals was associated with lower AMI RSMRs when compared with low volume hospitals:– High: OR=0.82 (0.79-0.85)– Moderate: OR=0.89 (0.86-0.93)

Volume & Observed HF Mortality

12.6% 12.1% 11.4%

0%

10%

20%

Low Moderate High

Volume & HF RSMR

• Admission to both high and moderate volume hospitals was associated with lower HF RSMRs when compared with low volume hospitals:– High: OR=0.85 (0.82-0.89)– Moderate: OR=0.93 (0.89-0.96)

Conclusions

• Hospital volume was associated with lower risk-standardized odds of death after admission both AMI and HF among FFS Medicare beneficiaries.

• For high volume hospitals, 18% lower odds for AMI, 15% for HF.

Limitations

• Focused only on mortality, not other important dimensions of quality.– i.e., processes of care, patient experiences.

• May not be generalized to other conditions or to care provided in ambulatory settings.

• Observational study – can not rule out confounding of hospital volume by other unmeasured variables.

Implications

• A relationship between volume and outcomes may exist for some medical conditions, as well as for surgical conditions and procedures.

• Provides some reassurance as quality organizations begin to use volume as a surrogate for quality.

Study Team

Yale University/Yale New-Haven Hospital• Yun Wang, PhD• Jersey Chen, MD• Judith H. Lichtman, PhD, MPH• Harlan M. Krumholz, MD, SM• Entire CORE teamHarvard University• Sharon-Lise T. Normand, PhDSunnybrook Health Sciences Centre• Dennis T. Ko, MD, MSc