Research Critique
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Research Article CritiqueKayla Muth
Article Overview Title
Prospective Study of Obstructive Sleep Apnea and Incident Coronary Heart Disease and Heart Failure: The Sleep Heart Health Study
Study began in 1994 and ended in 2006
Submitted August 2009
Accepted May 2010
Published in Circulation July 2010
Sources Publication dates ranged from 1975-2009
Selection of Journals and Studies American Journal of Cardiology American Journal of Medicine Circulation Framingham Heart Study Journal of the American Medical Association Journal of Applied Physiology New England Journal of Medicine Sleep
Definitions Obstructive Sleep Apnea (OSA)
Continuous Positive Airway Pressure Therapy
Community Based Prospective Cohort Study
Polysomnography
Electroencephalogram
Electrooculogram
Chin electromyogram
Inductance plethysmography
Apnea
Hypopnea
Apnea-hypopnea index (AHI)
Incident CHD
Incident Heart Failure
Cox proportional hazards regression modeling
Linear regression splines
LOWESS
Adjusted hazard ratio
Purpose of the Study “To assess the independent contribution of
OSA to cardiovascular disease, the Sleep Heart Health Study (SHHS) was initiated in 1994 as a multicenter, prospective cohort study of the cardiovascular consequences of OSA.”
“The present report details the incidence of CHD and heart failure in SHHS participants free of these conditions at the baseline examination.”
Study Design Adults 40 years of age and older were recruited
from existing population-based studies of cardiovascular and pulmonary disease
Participants completed questionnaires on sleep habits and general health
Height, weight, and blood pressure were measured
Underwent overnight polysomnography
Parent cohorts provided data
Ongoing surveillance for cardiovascular disease through April 2006
Study Sample 10,737 cohort participants invited to participate
6,441 were enrolled in study 760 participants from NYU-Cornell site excluded 783 participants excluded due to prevalent heart
disease or heart failure at baseline 21 participants lacked follow-up data and were
excluded 455 participants were missing baseline measures and
excluded
4,422 subjects remained for participation 2,495 females 1,927 males
Methods In-home polysomnography
Polysomnograms scored centrally and AHI determined
Ongoing surveillance for CHD and heart failure by parent-cohorts
Follow-up procedures performed by cohorts Median follow-up ranged from 8.3-9.2 years
All CHD and heart failure outcomes extracted from hospital and physician’s records by trained abstractors
~5 years post-baseline, survey relative to diagnosis of and treatment for OSA completed by 3,794 participants
Covariates Baseline prevalent CHD or
heart failure
Smoking status
Medication
Diabetes
Blood pressure
Weight
Race/ethnicity
Height
Total cholesterol
HDL cholesterol
Statistical Analysis Performed with SAS version 9.2
Descriptive statistics presented by category of OSA severity based on the AHI
Testing for improved model fit Cubic or quadratic functions Linear regression splines LOWESS
Association between sex and AHI Models created for males and females
Statistical Analysis cont.
Models using AHI as continuous dependent variable adjusted for the following independent variables: (1) Age, race, BMI, and smoking status (2) Variables from model (1) plus total and HDL
cholesterol and diabetes (3) Variables from model (2) plus hypertension
Models repeated using parent cohort instead of race
Models constructed to stratify age >70 years old ≤ 70 years old
Results Increasing severity with OSA was associated with
male sex, higher BMI, higher systolic blood pressure, lower HDL cholesterol, and higher prevalence of hypertension and diabetes
Median AHI in women was 2.7 (interquartile range 0.8 to 7.5) and 6.2 in men (interquartile range 2.3 to 14.3)
During follow-up period there were 473 incident CHD events 76 CHD deaths 185 MI’s 212 revascularization procedures
Results cont. During follow-up there were 308 incidents of
heart failure; 144 also had incident CHD
Rate of events increased with severity of OSA in men, but not as clearly in women
When adjusted for age, race, BMI, and smoking status there was a significant association between AHI with incident CHD in men
Discussion This study found an association between
incident CHD and OSA in men that was considerably weaker than previous clinic-based studies
Screening of non-clinic-based population identified many asymptomatic individuals with OSA
SHHS may underestimate the true cardiovascular risk associated with OSA due to median age of 62
Study demonstrates a 58% higher adjusted risk for incident heart failure for men with OSA
Strengths Community-based recruiting limited referral
bias
Detailed covariate data
Exclusion criteria provided
Few received treatment for OSA allowing for assessment of natural history of untreated OSA
Includes both men and women
Ethnically diverse
Weaknesses Older age of the cohort
Echocardiograms were not routinely performed
Varying protocols at different facilities
Varying frequency of follow-ups
Authors do not appear to be individuals who extracted data from medical records
BMI is imperfect way to collect anthropometric data
Diet and exercise not recorded
Significance Potentially significant because it does
suggest an increased risk of incident heart failure in those with OSA
Those with OSA tend to have all other risk factors predisposing them to heart disease, so it is hard to demonstrate if OSA has significant impact independent of those risk factors