Natural history of claudication: long-term serial follow-up study of 1244 claudicants.

OBJECTIVE: The purpose of this study was to delineate the natural history of claudication and determine risk factors for ischemic rest pain (IRP) and ischemic ulceration (IU) among patients with claudication. METHODS: We prospectively collected data on 1244 men with claudication during a 15-year period, including demographics, clinical risk factors, and ankle-brachial index (ABI). We followed these patients serially with ABIs, self-reported walking distance (WalkDist), and monitoring for IRP and IU. We used Kaplan-Meier and proportional hazards modeling to find independent predictors of IRP and IU. RESULTS: Mean follow-up was 45 months; statistically valid follow-up could be carried out for as long as 12 years. ABI declined an average of 0.014 per year. WalkDist declined at an average rate of 9.2 yards per year. The cumulative 10-year risks of development of IU and IRP were 23% and 30%, respectively. In multivariate analysis using several clinical risk factors, we found that only DM (relative risk [RR], 1.8) and ABI (RR, 2.2 for 0.1 decrease in ABI) predicted the development of IRP. Similarly, only DM (RR, 3.0) and ABI (RR, 1.9 for 0.1 decrease in ABI) were significant predictors of IU. CONCLUSION: This large serial study of claudication is, to our knowledge, the longest of its kind. We documented an average rate of ABI decline of 0.014 per year and a decline in WalkDist of 9.2 yards per year. Two clinical factors, ABI and DM, were found to be associated with the development of IRP and IU. Our findings may be useful in predicting the clinical course of claudication.

Outcome events in patients with claudication: a 15-year study in 2777 patients.

OBJECTIVE: The purpose of this study was to delineate the natural history of claudication and determine risk factors for death. METHODS: We reviewed the key outcomes (death, revascularization, amputation) in 2777 male patients with claudication identified over 15 years at a Veterans Administration hospital with both clinical and noninvasive criteria. Patients with rest pain or ulcers were excluded. Data were analyzed with life-table and Cox hazard models. RESULTS: The mean follow-up was 47 months. The cohort exhibited a mortality rate of 12% per year, which was significantly (P <.05) more than the age-adjusted US male population. Among the deaths in which the cause was known, 66% were due to heart disease. We examined several baseline risk factors in a multivariate Cox model. Four were significant (P <.01) independent predictors of death: older age (relative risk [RR] = 1.3 per decade), lower ankle-brachial index (RR = 1.2 for 0.2 change), diabetes requiring medication (RR = 1.4), and stroke (RR = 1.4). The model can be used to estimate the mortality rate for specific patients. Surprisingly, a history of angina and myocardial infarction was not a significant predictor. Major and minor amputations had a 10-year cumulative rate less than 10%. Revascularization procedures occurred with a 10-year cumulative rate of 18%. CONCLUSIONS: We found a high mortality rate in this large cohort and four independent risk factors that have a large impact on survival. Risk stratification with our model may be useful in determining an overall therapeutic plan for claudicants. A history of angina and myocardial infarction was not a useful predictor of death, suggesting that many patients in our cohort presented with claudication before having coronary artery symptoms. Our data also indicate that claudicants have a low risk of major amputation at 10-year follow-up.

Epidemiologic analysis of existing data to investigate hypertensive renal disease: an example from the Maryland End-Stage Renal Disease Registry.

Observational epidemiology provides powerful methods for studying the etiology and natural history of renal disease in populations. Existing data sets can be used in the conduct of cross-sectional, case-control, and cohort studies that complement experimental investigations. Analysis of existing data sets is extremely efficient and, in many instances, provides results of similar quality to those derived from studies that depend on the collection of original data. A study based on linkage of hypertensive end-stage renal disease (ESRD) incidence rates from the Maryland Regional ESRD Registry with corresponding prevalence data from a state-wide survey of cardiovascular risk factors (The Maryland Statewide Household Hypertension Survey) illustrates the power, efficiency, and flexibility of observational epidemiologic methods in investigating racial differences in hypertensive ESRD. Such analyses can both test previously established hypotheses and generate new hypotheses for subsequent investigation.

The excess incidence of diabetic end-stage renal disease among blacks. A population-based study of potential explanatory factors.

OBJECTIVE: To investigate whether the excess incidence of diabetic end-stage renal disease (ESRD) among African Americans could be explained by racial differences in putative ESRD risk factors. DESIGN: Population-based, ecologic study using the 1981 and 1982 Maryland Statewide Household Hypertension Survey for data on risk factor prevalence. PARTICIPANTS: A total of 2.1 million adults residing within the boundaries of the Maryland Regional ESRD Registry, grouped by race and ZIP code into 26 subpopulations. MAIN OUTCOME MEASURE: Incidence rates of treatment for diabetic ESRD between 1980 and 1985 from the Maryland Regional ESRD Registry by subpopulation. RESULTS: Between 1980 and 1985, 442 persons entered treatment for diabetic ESRD. At the level of the subpopulation, diabetic ESRD incidence was positively associated with black race (relative risk [RR], 3.42; 95% confidence interval [CI], 2.84 to 4.13), prevalence of diabetes (RR, 2.35; 95% CI, 1.92 to 2.87), prevalence of poorly controlled hypertension (RR, 1.80; 95% CI, 1.45 to 1.86), lack of a regular source of health care (RR, 1.82; 95% CI, 1.62 to 2.05), and lower socioeconomic status as indicated by lack of college education (RR, 1.41; 95% CI, 1.32 to 1.52) (all, P < .0001). After adjusting for these risk factors, black race remained strongly associated with the overall incidence of diabetic ESRD (RR, 2.70; 95% CI, 1.89 to 3.86; P < .0001). Further analyses suggested that this excess risk among blacks was confined to ESRD related to non-insulin-dependent diabetes (RR, 4.80; 95% CI, 3.09 to 7.46; P < .0001); blacks were at no higher risk than were whites for ESRD related to insulin-dependent diabetes (RR, 0.90; 95% CI, 0.52 to 1.55; P = .70). CONCLUSIONS: These data suggest that the excess incidence of diabetic ESRD among blacks is not fully explained by a higher prevalence of diabetes or hypertension in blacks or by racial differences in age, socioeconomic status, or access to health care. Instead, they suggest an increased susceptibility to ESRD resulting from non-insulin-dependent diabetes among blacks as compared with whites.

Does racial variation in risk factors explain black-white differences in the incidence of hypertensive end-stage renal disease?

Prospectively collected data on the incidence of treated hypertensive end-stage renal disease (HT-ESRD) were analyzed to investigate whether the higher rate of HT-ESRD in blacks compared with whites is due to differences in putative ESRD risk factors. The overall age-adjusted relative risks of HT-ESRD for black compared with white residents in the Maryland Regional ESRD Registry (Network 31) Catchment Area were 7.4 (95% confidence interval, 5.9 to 9.4) and 9.9 (95% confidence interval, 7.4 to 13.1) for men and women, respectively. In a population level analysis, race-specific HT-ESRD incidence rates in the black and white populations of 13 regions in Network 31 were related to the prevalence of putative ESRD risk factors in those populations. The latter were estimated from the 1981-1982 Maryland Statewide Household Hypertension Survey. Black populations had a 5.6-fold (95% confidence interval, 3.9 to 8.1) higher unadjusted incidence of HT-ESRD than white populations. The HT-ESRD incidence in a population was also directly related to that population's prevalence of hypertension, severe hypertension, and diabetes mellitus and inversely related to measures of socioeconomic status and mean age at diagnosis of hypertension. When adjusted simultaneously for age, prevalence of hypertension, severe hypertension, diabetes, and level of education, the risk of HT-ESRD was still 4.5 (95% confidence interval, 3.2 to 6.2) times higher for black compared with white populations. Our findings failed to support the hypothesis that race-related differences in the prevalence, severity, or age at onset of hypertension, in the prevalence of diabetes or in socioeconomic status, explain the well-recognized black-white differences in the HT-ESRD incidence.