Propensity-matched Population Research Articles

A propensity-matched study of low serum potassium and mortality in older adults with chronic heart failure

Objective Most HF patients are older adults, yet the associations of low serum potassium and outcomes in these patients are unknown. We studied the effect of low serum potassium in a propensity-matched population of elderly HF patients. Methods Of the 7788 patients in the Digitalis Investigation Group trial, 4036 were ≥ 65 years. Of these, 3598 had data on baseline serum potassium and 324 with potassium ≥ 5 mEq/L were excluded. Remaining patients were categorized into low (< 4 mEq/L; n = 590) and normal (4–4.9 mEq/L; n = 2684) potassium groups. Propensity scores for low-potassium, calculated for each patient, were used to match 561 low-potassium and 1670 normal-potassium patients. Association of low potassium and outcomes were assessed using matched Cox regression analyses. Results Patients had a mean (± SD) age of 72 (± 6) years, 29% were women and 12% were non-whites. Of the 561 low-potassium patients, 500 had low-normal (3.5–3.9 mEq/L) potassium. All-cause mortality occurred in 37% (rate, 1338/10,000 person-years) normal-potassium and 43% (rate, 1594/10,000 person-years) low-potassium patients (hazard ratio {HR} for low-potassium, 1.22; 95% confidence interval {CI}, 1.04–1.44; p = 0.014). Low-normal (3.5–3.9 mEq/L) potassium levels had a similar association with mortality (HR, 1.19, 95% CI, 1.00–1.41, p = 0.049). Low (HR, 1.10; 95% CI, 0.96–1.25; p = 0.175) or low-normal (HR = 1.09, 95% CI = 0.95–1.25, p = 0.229) serum potassium levels were not associated with all-cause hospitalization. Conclusions In a propensity-matched population of elderly ambulatory chronic HF patients, well-balanced in all measured baseline covariates, low and low-normal serum potassium were associated with increased mortality but had no association with hospitalization.

Low serum magnesium and cardiovascular mortality in chronic heart failure: A propensity-matched study

Background Low serum magnesium levels may cause fatal ventricular arrhythmias. However, their long-term effects on mortality and morbidity in chronic heart failure patients are relatively unknown. Methods We studied 1569 chronic systolic and diastolic heart failure patients with normal sinus rhythm who participated in the Digitalis Investigation Group trial and had serum magnesium data available at one month. Of these, 741 patients had normal (> 2 mEq/L) and 828 had low (≤ 2 mEq/L) serum magnesium levels. Propensity scores for having low serum magnesium levels were calculated for each patient using a non-parsimonious multivariable logistic regression model, and were used to match 560 (76%) low-magnesium patients with 560 normal-magnesium patients. Effects of low-magnesium on mortality and hospitalization during a mean follow-up of 36 months were assessed using matched Cox regression analyses. Results All-cause mortality occurred in 156 (rate, 915/10,000 person-years) normal- magnesium and 171 (rate, 1034/10,000 person-years) low-magnesium patients, respectively, during 1704 and 1653 years of follow-up (hazard ratio, 1.23; 95% confidence interval, 0.97–1.57; p = 0.089). Cardiovascular mortality occurred in 110 (rate, 646/10,000 person-years) normal-magnesium and 133 (rate, 805/10,000 person-years) low-magnesium patients (hazard ratio, 1.38, 95% confidence interval, 1.04–1.83, p = 0.024). Hazard ratios and 95% confidence intervals for all-cause and cardiovascular hospitalizations were respectively 1.18 (0.99–1.42; p = 0.068) and 1.14 (0.94–1.39; p = 0.182). Conclusions In a propensity-matched population of ambulatory chronic heart failure patients who were balanced in all measured baseline covariates, serum magnesium level 2 mEq/L or less was associated with increased cardiovascular mortality, but had no association with cardiovascular hospitalization.

Race and the Natural History of Chronic Heart Failure: A Propensity-Matched Study

Background Racial differences in the epidemiology and outcomes of heart failure are well known. However, the association of race with the natural history of heart failure has not been previously studied in a propensity-matched population of chronic heart failure in which all measured baseline patient characteristics are well-balanced between the races. Methods and Results Of the 7788 patients with chronic systolic and diastolic heart failure in the Digitalis Investigation Group trial, 1128 were nonwhites. Propensity scores for being nonwhite were calculated for each patient and were used to match 1018 pairs of white and nonwhite patients. Matched Cox regression analyses were used to estimate associations of race with outcomes during 38 months of median follow-up. All-cause mortality occurred in 34% (rate, 1180/10000 person-years) of whites and 33% (rate, 1130/10000 person-years) of nonwhite patients (hazard ratio when nonwhite patients were compared with whites, 0.95, 95% confidence interval, 0.80–1.14; P = .593). All-cause hospitalization occurred in 63% (rate, 3616/10000 person-years) of whites and 65% (rate, 3877/10000 person-years) of nonwhite patients (hazard ratio, 1.03, 95% confidence interval, 0.90–1.18; P = .701). Respective hazard ratios (95% confidence intervals) for other outcomes were: 0.95 (0.75–1.12) for cardiovascular mortality, 0.82 (0.60–1.11) for heart failure mortality, 1.05 (0.91–1.22) for cardiovascular hospitalization, and 1.17 (0.98–1.39) for heart failure hospitalization. Conclusions In a propensity-matched population of heart failure patients where whites and nonwhites were balanced in all measured baseline characteristics, there were no racial differences in major natural history end points.

Incident Heart Failure Hospitalization and Subsequent Mortality in Chronic Heart Failure: A Propensity-Matched Study

Objective Hospitalization for worsening heart failure (HF) is common and associated with high mortality. However, the effect of incident HF hospitalization (compared with no HF hospitalization) on subsequent mortality has not been studied in a propensity-matched population of chronic HF patients. Methods In the Digitalis Investigation Group trial, 5501 patients had no HF hospitalizations (4512 alive at 2 years after randomization) and 1732 patients had HF hospitalizations during the first 2 years (1091 alive at 2 years). Propensity scores for incident HF hospitalization during the first 2 years after randomization were calculated for each patient and used to match 1057 patients (97%) who had 2-year HF hospitalization with 1057 patients who had no HF hospitalization. We used matched Cox regression analysis to estimate the effect of incident HF hospitalization during the first 2 years after randomization on post–2-year mortality. Results Compared with 153 deaths (rate, 420/10,000 person-years) in the no HF hospitalization group, 334 deaths (rate, 964/10,000 person-years) occurred in the HF hospitalization group (hazard ratio 2.49; 95% confidence interval 1.97–3.13; P < .0001). The hazard ratios (95% confidence intervals) for cardiovascular and HF mortality were 2.88 (2.23–3.74; P < .0001) and 5.22 (3.34–8.15; P < .0001), respectively. Conclusions Hospitalization for worsening HF was associated with increased risk of subsequent mortality in ambulatory patients with chronic HF. These results highlight the importance of HF hospitalization as a marker of disease progression and poor outcomes in chronic HF, reinforcing the need for prevention of HF hospitalizations and strategies to improve postdischarge outcomes.