In-Hospital Mortality in Hospitalized Patients with Congestive Heart Failure in Relation to Serum Potassium Levels in the US: National Inpatient Sample Analysis

Abstract

Introduction: Alteration in serum potassium levels has been found to affect the mortality risk among patients with congestive heart failure (CHF). Methods: We utilized the National Inpatient Sample database. We selected patients (≥18 years and non-pregnant) admitted with CHF in US hospitals from 2009 to 2011. We substituted code for CHF (428) based on International Classification of disease-9 (ICD-9) with Clinical Classification Software-Diagnoses of 108. We added ICD-9 codes 404.03, 404.11, 404.13, 404.91, 404.93 and 402.11 to include all etiologies of heart failure. The ICD-9 codes for hypokalemia is 276.8 and hyperkalemia is 267.7. STATA version 13.0 (College Station, TX) was used for analysis. Multivariate analysis of mortality among CHF patients was done while controlling for age, sex, race, smoking, obesity, dyslipidemia, diabetes, hypertension and Charlson comorbidity index. Results: Our total study population was based on 2,660,609 discharge records. Hypokalemia was found to be associated with increased mortality risk (OR: 2.025) and hyperkalemia was associated with decreased mortality risk (OR: 0.935) in comparison to normokalemia (Table 1). Similar association was seen with etiologies (Acute coronary syndrome, Ischemic heart disease, valvular heart disease, hypertensive heart disease, cardiomyopathy, atrial fibrillation) and subtypes (systolic, diastolic and combined) of CHF with serum potassium levels (Table 2, Table 3). Discussion: Our study is the first to establish relationship of risk of mortality between subcategories of serum potassium levels with different etiologies and subtypes of CHF. Thus, regardless of the etiology or subtype of heart failure, hypokalemia increases mortality and hyperkalemia is associated with mortality benefit. Hypokalemia results from increased activation of Renin Angiotensin Aldosterone System. Low serum potassium increases the transmembrane resting potential of myocardial cells resulting in hyperpolarization and increased excitability. This increases risk of cardiac arrhythmias. Ventricular arrhythmias are the most common cause of death in these patients. Thus, normokalemia and hyperkalemia in patients admitted with CHF has a beneficial effect. This can be achieved by use of potassium supplements, ACE inhibitors and K-sparing diuretics. Whether correction of hypokalemia during hospital stay is beneficial or not is a matter of further studies.Table 1Multivariate analysis with logistic regression of mortality among CHF patients with hyperkalemia and hypokalemia with reference to normokalemia. (Controlled for age, sex, race, smoking, obesity, dyslipidemia, diabetes, hypertension, Charlson comorbidity index)Table 2Classification of mortality in relation to serum potassium levels in CHF and its subcategories. (CHF: congestive heart failure, SHF: systolic heart failure, DHF: diastolic heart failure, SDHF: systolic and diastolic heart failure)Table 2Classification of mortality in relation to serum potassium levels in CHF and its subcategories. (CHF: congestive heart failure, SHF: systolic heart failure, DHF: diastolic heart failure, SDHF: systolic and diastolic heart failure)Table 3Multivariate analysis with logistic regression of mortality among different etiologies of heart failure with hyperkalemia and hypokalemia with reference to normokalemia. (ACS: acute coronary syndrome, IHD: Ischemic heart disease, VHD: valvular heart disease, HHD: hypertensive heart disease, CM: cardiomyopathy, AF: atrial fibrillation)Table 3Multivariate analysis with logistic regression of mortality among different etiologies of heart failure with hyperkalemia and hypokalemia with reference to normokalemia. (ACS: acute coronary syndrome, IHD: Ischemic heart disease, VHD: valvular heart disease, HHD: hypertensive heart disease, CM: cardiomyopathy, AF: atrial fibrillation)