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
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 & 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 team Harvard University • Sharon-Lise T. Normand, PhD Sunnybrook Health Sciences Centre • Dennis T. Ko, MD, MSc