By Michael H. Crawford, MD
Professor of Medicine, Associate Chief for Education, Division of Cardiology, University of California, San Francisco
Dr. Crawford reports no financial relationships relevant to this field of study.
SYNOPSIS: A large, long-term, prospective, Norwegian population study of patients with established atrial fibrillation revealed physical activity at or above recommended levels reduces all-cause and cardiovascular mortality vs. atrial fibrillation patients who are inactive.
SOURCE: Garnvik LE, Malmo V, Janszky I, et al. Physical activity, cardiorespiratory fitness, and cardiovascular outcomes in individuals with atrial fibrillation: The HUNT study. Eur Heart J 2020;41:1467-1475.
Persistent atrial fibrillation (AF) is associated with higher rates of morbidity and mortality. When AF accompanies almost every other disease, the prognosis is much worse. Physical activity (PA) is known to reduce the incidence of AF, but little is known about its value in established AF.
Garnvik et al evaluated data from the third wave of the Nord-Trøndelag Health Study (HUNT 3) from the northern region of Norway. Their goal was to assess the effect of PA and cardiorespiratory fitness (CRF) on all-cause mortality as well as cardiovascular (CV) mortality and morbidity in patients with documented AF and those free of AF. Clinical data were obtained from hospital and physician office records using standard criteria. Information on PA was obtained using a validated questionnaire, with details about frequency, intensity, and duration of exercise. Patients were classified as inactive, below recommended exercise levels, or at/above recommended exercise levels. CRF was estimated using a validated non-exercise method based on sex, age, waist circumference, resting heart rate, and PA. Patients in HUNT 3 were enrolled between 2006 and 2008 and followed until death, their first CV event, or 2015. Data analysis was adjusted for multiple clinical variables that could influence the results.
From 50,802 participants in HUNT 3, 1,117 with AF not related to an acute stressful event and with complete data were included. Approximately two-thirds of the study population were men (average age about 70 years; about 60% had persistent or permanent AF). AF patients meeting recommended PA levels recorded a significantly lower all-cause mortality rate than inactive patients (hazard ratio [HR], 0.55; 95% confidence interval [CI], 0.81-0.95), as did those with highest CRF levels vs. the lowest quartile (HR, 0.64; 95% CI, 0.47-0.89). CV mortality also was significantly lower in patients meeting or exceeding recommendations vs. inactive patients (HR, 0.54; 95% CI, 0.34-0.86) and those in the highest vs. lowest CRF quartile (HR, 0.61; 95% CI, 0.38-0.98).
CV morbidity and stroke rates were lower in patients at or above the recommended PA level and in those with higher CRF. CV mortality also was lowest with patients on moderate-intensity exercise vs. inactive patients (HR, 0.50) and vigorous activity vs. inactivity (HR, 0.70). AF patients who met recommended PA experienced similar rates of all-cause mortality, CV mortality, and stroke as inactive, non-AF patients. Sensitivity analyses showed the benefits of PA were not significant in obese patients (body mass index > 30 kg/m2). Men benefitted more from higher CRF than women. The authors concluded that higher PA and CRF reduced the long-term risk of all-cause and CV mortality in patients with AF.
The health benefits of PA and enhanced CRF has been shown in healthy populations and certain disease states (e.g., post-myocardial infarction). Also, recent studies have shown PA and CRF can prevent AF, but there are few data about their effects on established AF. Nevertheless, this is important because the symptoms of AF, medications used, and comorbidities often discourage patients from exercising. That is why this study is of interest. Norway would seem to be ideal for a study like the one Garnvik et al conducted. One might expect the prevalence of AF to be high since the genetic component of AF is most common in those of Northern European descent. Additionally, Norway’s national health system mandates the reporting of patient outcomes. Finally, Norwegians seem to enjoy participating in such studies because > 50% of the entire population of Nord-Trøndelag County participated in the HUNT 3 investigation. Other strengths of the Garnvik et al study included the prospective design and the long-term follow-up of about eight years. Finally, the diagnosis of AF was well validated.
There were several limitations, most importantly the association between PA/CRF and lower all-cause and CV mortality rates does not confirm causality, nor does it elucidate the mechanism of any potential benefits observed. AF may just be a marker for CV disease. Also, it is unclear whether the PA reported was occurring before or after the AF diagnosis. PA may just be a continuation of a patient’s routine. Thus, prescribing exercise to a sedentary patient may not be effective. Other limitations included the fact that PA was self-reported and CRF was estimated rather than measured. The formula to estimate CRF includes resting heart rate, which could be problematic in AF. The authors did not report any data on medications or the progression of AF over time. The low rate in women, about one-third of the study population, is concerning since this would not be expected.
Despite these limitations, the results of this study support a role for regular PA and improved CRF in AF patients to help prevent the reported higher incidence of morbidity and mortality. Those AF patients who engaged in the most strenuous PA/CRF recorded event-free survival curves that approximated the inactive members of the non-AF general population.