Impact of a Multidisciplinary Heart Failure Post-hospitalization Program on Heart Failure Readmission Rates.

BACKGROUND: Specialized chronic heart failure (HF) clinics have demonstrated significant reductions in readmissions. Limited evidence is available regarding HF clinics in the immediate post-discharge period. OBJECTIVE: To evaluate the effect of a multidisciplinary HF clinic on 90-day readmission rates and all-cause mortality in those recently discharged from a HF hospitalization. METHODS: In this retrospective cohort study, patients discharged with a primary HF diagnosis who attended the HF postdischarge clinic in 2010-2012 were compared with controls from 2009. During 6 clinic visits, patients were seen by a physician assistant, clinical pharmacist specialist, and case manager, with care overseen by a cardiologist. The program focused on optimizing therapy, identifying HF etiology/precipitating factors, medication titration, education, and medication adherence. The primary outcome was 90-day HF readmission. A multivariate Cox proportional hazards model was used to compare outcomes. RESULTS: Among the 277 patients (144 clinic, 133 control) in the study, 7.6% of patients in the clinic and 23.3% of patients in the control group were readmitted for HF within 90 days (aHR (adjusted hazard ratio) = 0.17; 95% CI = 0.07-0.41; P < 0.001; ARR (absolute risk reduction) = 15.7%; NNT (number needed to treat) = 7). Clinic patients had lower 90-day time-to-first HF readmission or all-cause mortality (9.0% vs 28.6%; aHR = 0.28; 95% CI = 0.06-0.31; P < 0.001; ARR = 19.6%; NNT = 6). CONCLUSIONS: The multidisciplinary HF posthospitalization outpatient program was associated with a significant reduction in 90-day HF readmissions in patients who were recently discharged from a HF hospitalization.

Prehypertension, hypertension, and the risk of acute myocardial infarction in HIV-infected and -uninfected veterans.

BACKGROUND: Compared to uninfected people, human immunodeficiency virus (HIV)-infected individuals may have an increased risk of acute myocardial infarction (AMI). Currently, HIV-infected people are treated to the same blood pressure (BP) goals (<140/90 or <130/80 mm Hg) as their uninfected counterparts. Whether HIV-infected people with elevated BP have excess AMI risk compared to uninfected people is not known. This study examines whether the association between elevated BP and AMI risk differs by HIV status. METHODS: The Veterans Aging Cohort Study Virtual Cohort (VACS VC) consists of HIV-infected and -uninfected veterans matched 1:2 on age, sex, race/ethnicity, and clinical site. For this analysis, we analyzed 81 026 people with available BP data from VACS VC, who were free of cardiovascular disease at baseline. BP was the average of the 3 routine outpatient clinical measurements performed closest to baseline (first clinical visit after April 2003). BP categories used in the analyses were based on criteria of the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Analyses were performed using Cox proportional hazards regression. RESULTS: Over 5.9 years (median), 860 incident AMIs occurred. Low/high prehypertensive and untreated/treated hypertensive HIV-infected individuals had increased AMI risk compared to uninfected, untreated normotensive individuals (hazard ratio [HR], 1.60 [95% confidence interval {CI}, 1.07-2.39]; HR, 1.81 [95% CI, 1.22-2.68]; HR, 2.57 [95% CI, 1.76-3.76]; and HR, 2.76 [95% CI, 1.90-4.02], respectively). CONCLUSIONS: HIV, prehypertensive BP, and hypertensive BP were associated with an increased risk of AMI in a cohort of HIV-infected and -uninfected veterans. Future studies should prospectively investigate whether HIV interacts with BP to further increase AMI risk.

Cardiac Electrical and Structural Changes after Iodinated Contrast Media Administration: A Longitudinal Cohort Analysis.

Background: Iodinated contrast is commonly used for radiological procedures, with one dose delivering several hundred-fold the daily requirements needed for normal thyroid hormone production. Risks of excess iodine include incident thyroid dysfunction, which is associated with adverse cardiac outcomes, yet there are no prospective studies investigating the changes in cardiac physiology following iodine contrast administration. This study was conducted to investigate the longitudinal relationships between the amount of iodinated contrast administration and changes in cardiac electrophysiology and structure. Methods: A longitudinal cohort study was conducted with prospectively enrolled participants who received iodine contrast for elective computed tomography or coronary angiography. Serum thyroid function tests, electrocardiograms (EKG), and transthoracic echocardiograms were obtained serially until 36 months. Trends of electrical and structural cardiac changes following iodine contrast administration were assessed using mixed effect models. Results: The cohort was composed of 129 patients (median age, 70 [interquartile range: 63, 75] years; 98% male). Larger amounts of iodine exposure were associated with increases in QRS and QTc durations and decreased ejection fraction (EF), and these associations were still observed for follow-up EF after additionally adjusting for baseline values (the high-iodine contrast group vs. the low-iodine contrast group, -4.23% [confidence interval, -7.66% to -0.79%]). Dose-response analyses also showed lower EF with larger amounts of iodine received; these trends were not significant for the EKG parameters studied. Conclusions: Over a period of up to 36 months, a larger amount of administered iodine contrast was associated with lower EF among participants. Further investigation is needed to elucidate the long-term trends of electrical and structural cardiac function after iodine contrast administration.

Left Atrial Mechanics and Diastolic Function Among People Living With Human Immunodeficiency Virus (from the Veterans Aging Cohort Study).

Human immunodeficiency virus (HIV) infection is associated with subclinical cardiomyopathy, diastolic dysfunction, and increased risk of cardiovascular death. However, the relationship between left atrial (LA) mechanics and left ventricular (LV) diastolic function has not been evaluated in people living with HIV (PLWH) relative to HIV-uninfected (HIV-) controls. This is a multicenter, cross-sectional cohort analysis using the HIV Cardiovascular Disease substudy of the Veterans Aging Cohort Study database, which aimed to examine a cohort of PLWH and HIV- veterans without known cardiovascular disease. A total of 277 subjects (180 PLWH, 97 HIV-) with echocardiograms were identified. LV and LA phasic strain were derived and diastolic function was evaluated. Relationship between LA strain, LV strain, and the degree of diastolic dysfunction were assessed using analysis of variance and ordinal logistic regression with propensity weighting. In the PLWH cohort, 91.7% were on antiretroviral therapy and 86.1% had HIV viral loads <500 copies/ml. The mean (± SD) duration of infection was 9.7 ± 4.9 years. Relative to HIV- veterans, PLWH did not differ in LA mechanics and proportion of diastolic dysfunction (p = 0.31). Using logistic regression with propensity weighting, we found no association between HIV status and degree of diastolic dysfunction. In both cohorts, LA reservoir strain and LA conduit strain were inversely and independently associated with the degree of diastolic dysfunction. Compared with HIV- veterans, PLWH who are primarily virally suppressed and antiretroviral-treated did not differ in LA strain or LV diastolic dysfunction. If confirmed in other cohorts, HIV viral suppression may curtail adverse alterations in cardiac structure and function.

Inpatient Quality-of-Care Measures for Heart Failure: Treatment Gaps and Opportunities in the Contemporary Era.

BACKGROUND: Quality of care measures are vital tools to assess processes of care within and between health care systems. The 2020 American College of Cardiology/AHA performance measures for heart failure provide a new set of such measures. We evaluated the achievement of these and other performance measures within the Veterans Affairs hospital system in a contemporary cohort of patients hospitalized for heart failure. METHODS: Hospital discharges from January 2010 to February 2021 with a primary diagnosis of heart failure (n=289 810) were evaluated. Adherence to each measure was determined using the measure's stated definition and by site. RESULTS: Among patients with reduced ejection fraction (53.0%), beta blocker use was high (89.0%), ACE (angiotensin-converting enzyme) inhibitor, angiotensin receptor blocker, or angiotensin receptor-neprilysin inhibitor (ARNI) use decreased over time (75.3% in 2010, 55.8% in 2020), and hydralazine/nitrate use in eligible Black patients (19.3%) was low. While 68.1% were eligible for ARNI, only 6.0% received them, reaching 17.2% by 2020. Mineralocorticoid receptor antagonists were used in 49.3% of those eligible; laboratory testing 7 days after their initiation was 73.0%, detecting hyperkalemia in 2.2%, although it occurred in 13.7% by 90 days. Achievement of ≥50% target dose was low (beta blocker 45.9%, ACE inhibitor/angiotensin receptor blocker 31.6%, ARNI 19.0%) and for ACE inhibitor/angiotensin receptor blocker/ARNI, decreased over time. Discharge appointments were 56.2% at 7 days and 78.8% at 14 days. Cardiac rehabilitation referral was low (10.5%) but increased. There were significant site-level differences, particularly for hydralazine, ARNI, devices, and cardiac rehabilitation. CONCLUSIONS: Important inpatient quality of care measures can be readily measured across the Veterans Administration health care system from electronic health records. Treatment gaps and site-level differences persisted into the contemporary era and will likely be exacerbated as newer treatments are added to this complex baseline. These measures and methods also offer the opportunity to target global, local, and individual processes of care for innovative quality improvement initiatives.

Advances in the treatment of transthyretin cardiac amyloidosis: Current and emerging therapies.

Transthyretin cardiac amyloidosis (ATTR-CA) has been recognized as an underdiagnosed and undertreated cause of heart failure with often unrecognized multiorgan involvement. Guideline development and the establishment of nonbiopsy criteria for diagnosis of ATTR-CA have led to an increased rate of diagnosis and hence patients referred for therapies. ATTR is a protein misfolding disorder where the TTR tetramer disassociates into monomers which form insoluble amyloid depositions in organs, including the heart. ATTR-CA can be due to autosomal dominant transmitted gene mutation or due to misfolding of wild-type TTR. Prior to 2019, there were no FDA-approved pharmacological treatments for ATTR-CA. Understanding of ATTR-CA pathogenesis has enabled development of targeted strategies with novel disease-modifying therapies. Current and emerging therapies for ATTR-CA include (1) TTR gene silencing (siRNA, ASO, CRISPR/Cas9), (2) TTR tetramer stabilization, and (3) TTR amyloid fibril degradation. This review focuses on the pathophysiology of ATTR-CA, diagnostic criteria, and addresses current and emerging treatments for this diverse disorder.

Bleeding Risk of Direct Oral Anticoagulants in Patients With Heart Failure And Atrial Fibrillation.

BACKGROUND: Patients with heart failure and atrial fibrillation are an important atrial fibrillation subgroup in which direct oral anticoagulants (DOACs) have not been adequately studied in real-world settings. Since DOACs rely on renal elimination and renal dysfunction is prevalent in patients with heart failure, their use may increase bleeding risk, negating some of their advantage over warfarin. METHODS: We conducted a retrospective cohort study using linked Veterans Administration databases of patients with heart failure newly started on warfarin or DOACs for atrial fibrillation from October 2010 to August 2017 (23 635 warfarin, 25 823 DOAC). Outcomes included time to first bleeding, stroke, and death using Cox proportional hazards models with inverse probability of treatment weighting. RESULTS: Total bleeding (hazard ratio, 0.62 [95% CI, 0.56-0.68]), major bleeding (hazard ratio, 0.49 [95% CI, 0.40-0.61]), and death (hazard ratio, 0.74 [95% CI, 0.71-0.78]) were lower with DOAC than warfarin, and with apixaban and dabigatran, but not rivaroxaban. Moderate/severe chronic kidney disease was common (48.7%); moderate chronic kidney disease was associated with increased bleeding with DOACs but not warfarin. However, death and bleeding remained lower with DOACs than warfarin across all renal function levels and clinical subgroups. A >20% transient/persistent decline in renal function occurred in 53% of DOAC-treated patients at some point during follow-up, would have required dose reduction in 10.5% of patients, and was associated with increased bleeding. Dose adjustments were made more often, and bleeding and death were lower in patients seen by pharmacists or anticoagulation clinics. There were significant between-site variations in DOAC dosing. CONCLUSIONS: DOACs overall, apixaban, and dabigatran, but not rivaroxaban, were associated with less total bleeding and death than warfarin in patients with heart failure and atrial fibrillation at all levels of renal function. Renal function decline resulted in increased bleeding in patients with DOACs. DOAC dose adjustment was often indicated, associated with increased bleeding when not adjusted, emphasizing the need for closer monitoring in these patients.

DISCOVERY: prevalence of transthyretin (TTR) mutations in a US-centric patient population suspected of having cardiac amyloidosis.

BACKGROUND: Hereditary transthyretin-mediated amyloidosis (hATTR amyloidosis) is a multisystem disease that presents with polyneuropathy and/or cardiomyopathy. METHODS: DISCOVERY, a multicenter screening study, enrolled patients with clinically suspected cardiac amyloidosis to determine the frequency of transthyretin (TTR) mutations and assess disease characteristics. RESULTS: Of 1007 patients, the majority were from the US (84%), Black/African American (56%), male (63%), and with a mean (standard deviation) age of 65 (13) years. Among 1001 patients with genotyping results, 74 (7%) had a pathogenic TTR mutation (71/836 [8%] from the US). Val122Ile was the most common mutation, found in 11% of Black/African American patients overall; Black/African American ethnicity was an independent predictor of having a pathogenic TTR mutation. Additional independent predictors of such mutations in the total population and Black/African American group were interventricular septum thickness, low electrocardiogram voltage, and age. CONCLUSIONS: Pathogenic TTR mutations occurred in 8% of US patients with suspected cardiac amyloidosis. Most mutations were Val122Ile, almost exclusively found in Black/African American patients. Disease often remains undetected until advanced and difficult to treat, therefore, clinicians should assess at-risk patients for hATTR amyloidosis as early as possible.

Association of Syndemic Unhealthy Alcohol Use, Cigarette Use, and Depression With All-Cause Mortality Among Adults Living With and Without HIV Infection: Veterans Aging Cohort Study.

BACKGROUND: The prevalence and risk of concurrent unhealthy drinking, cigarette use, and depression on mortality among persons living with HIV (PLWH) is unclear. This study applied a syndemic framework to assess whether these co-occurring conditions increase mortality and whether such risk is differential by HIV status. METHODS: We evaluated 6721 participants (49.8% PLWH) without baseline cancer from the Veterans Aging Cohort Study, a prospective, observational cohort of PLWH and matched uninfected veterans enrolled in 2002 and followed through 2015. Multivariable Cox proportional hazards regressions estimated risk of a syndemic score (number of conditions: that is, unhealthy drinking, cigarette use, and depressive symptoms) on all-cause mortality by HIV status, adjusting for demographic, health status, and HIV-related factors. RESULTS: Fewer than 10% of participants had no conditions; 25.6% had 1, 51.0% had 2, and 15.0% had all 3. There were 1747 deaths (61.9% PLWH) during the median follow-up (11.4 years). Overall, age-adjusted mortality rates/1000 person-years increased with a greater number of conditions: (0: 12.0; 1: 21.2; 2: 30.4; 3: 36.3). For 3 conditions, the adjusted hazard ratio of mortality was 36% higher among PLWH compared with uninfected participants with 3 conditions (95% confidence interval, 1.07-1.72; P = .013), after adjusting for health status and HIV disease progression. Among PLWH and uninfected participants, mortality risk persisted after adjustment for time-updated health status. CONCLUSIONS: Syndemic unhealthy drinking, cigarette use, and depression are common and are associated with higher mortality risk among PLWH, underscoring the need to screen for and treat these conditions.

Safety of Alpha-Adrenergic Receptor Antagonists in Heart Failure.

OBJECTIVES: This study evaluated whether alpha-blocker (AB) use following an admission for heart failure (HF) was associated with an increased risk of HF readmission or death. BACKGROUND: ABs, found to increase the risk of HF in the ALLHAT (Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial) trial, are commonly used for prostatic hypertrophy, including in those with or at risk for HF. METHODS: This propensity score-matched cohort study included patients discharged from a Veterans Affairs hospital between January 2002 and September 2015 with a primary diagnosis of HF and ascertained AB use at discharge. Cox proportional hazards models were constructed to compare time to first HF readmission and death at 2 years between groups. Secondary analyses assessed effects by AB dose and type and by beta-blocker (BB) use. RESULTS: Of 169,911 HF patients, 47,638 (28%) were prescribed an AB. Propensity score matching resulted in 35,713 matched pairs. In the propensity score-matched cohort, AB use was associated with fewer HF readmissions (39.8% vs. 41.7% at 2 years; hazard ratio: 0.95; 95% confidence interval [CI]: 0.92 to 0.97; p < 0.0001) and death (42.8% vs. 46.5%; hazard ratio: 0.93; 95% CI: 0.91 to 0.94; p < 0.0001). Nonselective ABs had fewer deaths and HF readmissions (p < 0.0001), while higher AB doses reduced mortality (p < 0.0001). AB treatment was associated with reduced deaths in both BB-treated and untreated patients, with no increase in HF. CONCLUSIONS: Treatment of HF patients with an AB was associated not with a higher but instead with a lower rate of HF readmission and death. Higher doses and nonselective ABs were also associated with lower mortality, regardless of BB use. ABs may be used safely in HF patients where clinically indicated. The finding of improved outcomes with ABs may warrant further study.

Impact of a Multidisciplinary Heart Failure Postdischarge Management Clinic on Medication Adherence.

PURPOSE: Disease management programs have been associated with improved adherence to heart failure (HF) medications. However, there remain limited data on the benefit of a comprehensive multidisciplinary HF postdischarge management (PDM) clinic that promptly follows HF-related hospitalization on evidence-based HF medication adherence. OBJECTIVE: The aim of this study was to evaluate the effects of an HF-PDM clinic on adherence to evidence-based HF medication therapy. METHODS: In this retrospective cohort study, we identified patients discharged from the Veterans Affairs Greater Los Angeles Healthcare System between 2009 and 2012 with a primary diagnosis of HF. Data from patients who attended the HF-PDM clinic immediately following HF-related hospitalization between 2010 and 2012 were compared with those from historical controls, who did not attend the HF-PDM clinic, from 2009. The main outcome was adherence to evidence-based HF medications during the 90 days after discharge. Adherence was defined as the proportion of days covered at 90 days after discharge (PDC-90) of ≥0.80. The percentages of patients adherent to each medication were compared between the 2 groups using the χ2 test. A logistic regression model adjusted for potential confounding variables was constructed to evaluate the percentages of patients adherent to evidence-based HF medications. FINDINGS: A total of 277 patients (144 clinic, 133 control) were included in the study. Both univariate and multivariate analyses showed that the clinic was associated with improved medication adherence to angiotensin-converting enzyme inhibitors, a twice-daily ß-blocker, and aldosterone antagonists compared with controls. The most significant increases were in adherence to angiotensin-converting enzyme inhibitors, with mean PDC-90 values of 0.84 (control) versus 0.93 (clinic) (P = 0.008) and 90-day adherence rates of 69% (control) versus 87% (clinic) (P = 0.005). IMPLICATIONS: Care in the multidisciplinary HF-PDM clinic was associated with significant increases in 90-day adherence to evidence-based HF medications in patients who were recently discharged after an HF-related hospitalization.

The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study: approaches to control rate in atrial fibrillation.

OBJECTIVES: We sought to evaluate approaches used to control rate, the effectiveness of rate control, and switches from one drug class to another in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study. BACKGROUND: The AFFIRM study showed that atrial fibrillation (AF) can be treated effectively with rate control and anticoagulation, but drug efficacy to control rate remains uncertain. METHODS: Patients (n = 2,027) randomized to rate control in the AFFIRM study were given rate-controlling drugs by their treating physicians. Standardized rate-control efficacy criteria developed a priori included resting heart rate and 6-min walk tests and/or ambulatory electrocardiographic results. RESULTS: Average follow-up was 3.5 +/- 1.3 years. Initial treatment included a beta-adrenergic blocker (beta-blocker) alone in 24%, a calcium channel blocker alone in 17%, digoxin alone in 16%, a beta-blocker and digoxin in 14%, or a calcium channel blocker and digoxin in 14% of patients. Overall rate control was achieved in 70% of patients given beta-blockers as the first drug (with or without digoxin), 54% with calcium channel blockers (with or without digoxin), and 58% with digoxin alone. Adequate overall rate control was achieved in 58% of patients with the first drug or combination. Multivariate analysis revealed an association between first drug class and several clinical variables. There were more changes to beta-blockers than to the other two-drug classes (p < 0.0001). CONCLUSIONS: Rate control in AF is possible in the majority of patients with AF. Beta-blockers were the most effective drugs. To achieve the goal of adequate rate control in all patients, frequent medication changes and drug combinations were needed.

Predictors of erythropoietin use in patients with cardiorenal anaemia syndrome.

OBJECTIVES: Chronic kidney disease (CKD) and anemia are common in patients with heart failure (HF) - these 3 conditions have been coined the Cardiorenal Anemia Sydrome (CRAS). The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF-K/DOQI) guidelines do not specifically address patients with CRAS, creating uncertainty in erythropoietin (EPO) prescribing. We sought to determine predictors of EPO use in patients with CRAS. METHODS: We conducted a retrospective cohort study at the Veteran's Affairs Greater Los Angeles Healthcare System (VAGLAHS), a 300+ bed facility that provides primary and tertiary inpatient, and ambulatory care services, between January 1, 2003 to December 31, 2006. A multiple logistic regression model was constructed to identify predictors of EPO use among CRAS patients. KEY FINDINGS: Of 2058 patients with CRAS, 213 (10.3%) were prescribed EPO. There were significant differences in baseline characteristics between the EPO and non-EPO groups. The following predictors were found to be associated with EPO prescription: iron supplementation (odds ratio [OR] 52.70, 95% confidence interval [CI] 11.70-237.46), renal clinic appointment (OR 2.60, 95% CI 1.79-3.76), malignancy (OR 1.52, 95% CI 1.07-2.16) and use of hydralazine/nitrates (OR 1.41, 95% CI 1.03-1.92). There was an inverse association found between EPO prescription and baseline hemoglobin (OR 0.61, 95% CI 0.53-0.70) and eGFR (OR 0.96, 95% CI 0.94-0.97). CONCLUSION: A small proportion of patients eligible for EPO therapy according to guidelines at the time of the study were prescribed the indicated therapy. Markers of declining renal function or those suggesting need for anemia therapy were identified as EPO predictors.

HIV infection, cardiovascular disease risk factor profile, and risk for acute myocardial infarction.

BACKGROUND: Traditional cardiovascular disease risk factors (CVDRFs) increase the risk of acute myocardial infarction (AMI) among HIV-infected (HIV+) participants. We assessed the association between HIV and incident AMI within CVDRF strata. METHODS: Cohort-81,322 participants (33% HIV+) without prevalent CVD from the Veterans Aging Cohort Study Virtual Cohort (prospective study of HIV+ and matched HIV- veterans) participated in this study. Veterans were followed from first clinical encounter on/after April 1, 2003, until AMI/death/last follow-up date (December 31, 2009). Predictors-HIV, CVDRFs (total cholesterol, cholesterol-lowering agents, blood pressure, blood pressure medication, smoking, diabetes) used to create 6 mutually exclusive profiles: all CVDRFs optimal, 1+ nonoptimal CVDRFs, 1+ elevated CVDRFs, and 1, 2, 3+ major CVDRFs. Outcome-Incident AMI [defined using enzyme, electrocardiogram (EKG) clinical data, 410 inpatient ICD-9 (Medicare), and/or death certificates]. Statistics-Cox models adjusted for demographics, comorbidity, and substance use. RESULTS: Of note, 858 AMIs (42% HIV+) occurred over 5.9 years (median). Prevalence of optimal cardiac health was <2%. Optimal CVDRF profile was associated with the lowest adjusted AMI rates. Compared with HIV- veterans, AMI rates among HIV+ veterans with similar CVDRF profiles were higher. Compared with HIV- veterans without major CVDRFs, HIV+ veterans without major CVDRFs had a 2-fold increased risk of AMI (HR: 2.0; 95% confidence interval: 1.0 to 3.9; P = 0.044). CONCLUSIONS: The prevalence of optimal cardiac health is low in this cohort. Among those without major CVDRFs, HIV+ veterans have twice the AMI risk. Compared with HIV- veterans with high CVDRF burden, AMI rates were still higher in HIV+ veterans. Preventing/reducing CVDRF burden may reduce excess AMI risk among HIV+ people.

4-aminopyridine influences heart rate variability in long-standing spinal cord injury.

Humans with traumatic spinal myelopathy exhibit intralesional conduction block and autonomic failure as pathophysiologic sequelae of their injury. Analysis of heart rate variability (HRV) provides a means of assessing changes in the function of the autonomic nervous system (ANS) and the cardiac sequelae of injury. Thirteen patients with long-standing spinal cord injury (SCI) and 13 able-bodied controls were studied. Each patient received a single 10-mg dose of an immediate release (IR) formulation of 4-aminopyridine (4-AP). Twenty-four hour heart rate (HR) and HRV data were acquired using a Holter ambulatory electrocardiographic (ECG) monitor. Analysis of acquired data was carried out using a minicomputer programmed to separate ECG R-R intervals into frequency patterns that appear as peaks dispersed along a frequency range of 0.0 to 1.0 Hz. Twenty-four hour baseline, pretreatment low-frequency (LF) HRV power was diminished in all patients with SCI compared with able-bodied-controls and was significantly decreased in tetraplegic patients (P = 0.03). This difference in LF HRV power disappeared during the 24 hours immediately after administration of 4-AP, and mean LF HRV power in tetraplegic patients became indistinguishable from LF HRV power in controls. 4-Aminopyridine appears to influence ANS function and LF HRV in humans with long-standing SCI.