When Endurance Training Can Be Deadly for Older Athletes

An 80-year-old male arrives via ambulance at a hospital emergency department in Tucson, Arizona. He is unconscious, with a Glasgow Coma Scale of 3, and has sustained obvious head trauma after a suspected fall. It is 6 p.m.

He is accompanied by his wife, who explains that she found him unresponsive on the floor at home and called the ambulance immediately. She says he seemed fine when they went to bed at 10 p.m. the night before. She describes the patient as healthy and very active -- for example, he's a life-long runner who has completed many marathons, and does not smoke or drink alcohol.

Physical examination is significant for an intubated male with bradycardia at a rate of 40-50 beats per minute, a large right-sided hematoma overlying the skull, and right hemiplegia and hyperreflexia. Differential diagnoses include stroke, mechanical fall, syncope, cardiac arrest, arrhythmia, subdural/epidural/subarachnoid hemorrhage, and neoplasm.

Imaging Findings

Head computed tomography (CT) without contrast reveals a right subdural hemorrhage continuous with an intraparenchymal hematoma, with the largest dimensions measuring 4.6 × 2.8 cm.

CT angiogram reveals a proximal occlusion of the M2 branch of the left middle cerebral artery (MCA) with mild atherosclerotic disease in the bilateral internal carotid arteries.

Initial magnetic resonance imaging (MRI) confirms an infarct affecting the left middle cerebral artery MCA territory.

Clinicians performing the CT scan observe that the patient has extensor posturing. They administer a loading dose of levetiracetam, normal saline at 125 mL/hour, and place him on a permissive hypertension protocol with a systolic goal less than 160 mm Hg.

Due to the extensive intra­cranial bleeding, the patient is not a candidate for tissue plasminogen activator therapy. He is admitted to the neuro-intensive care unit. Echocardiography identifies severe bilateral atrial dilation with no shunting on bubble study; his left ventricle ejection fraction is 63%.

Hospital Day 2

A singular 5-minute episode of atrial fibrillation (AF) is noted on telemetry and captured on electrocardiogram (ECG). Clinicians compare the patient's ECG at the time of presentation with those from 3 years earlier in the electronic medical record, which reveal sinus bradycardia that meets the criteria for interatrial block (Bayés syndrome), a strong predictor of AF.

The patient's retrospective CHADS₂ score is 2 (intermediate stroke risk, 4.0% event/year) and CHA₂DS₂-VASc score is 3 (moderate-high stroke risk, 3.2% event/year); however, records show that he had never received anticoagulant medication.

Hospital Day 4: The patient's clinical course fails to improve. A second MRI shows extension of the left MCA territory infarct and a newly visualized right cerebellar infarct. The findings suggest little likelihood of meaningful recovery. As indicated by the family and in keeping with the patient's wishes, he is transitioned to comfort care.

Hospital Day 5: The patient is extubated and succumbs shortly thereafter.

Discussion

The clinician reporting this case of a fit 80-year-old male who suffers a fatal thromboembolic stroke thought to be due to undiagnosed paroxysmal AF highlights the importance of thorough investigation and a high index of suspicion for AF in asymptomatic older adults with a history of endurance athletic training.

Based on the evidence, the case author concludes that the patient suffered a stroke caused by thromboembolism secondary to undiagnosed paroxysmal AF.

This hypothesis is supported by the following findings:

• Evidence of atrial dilation measured by the parasternal long axis view greater than the 95th percentile compared with age-matched healthy adults

• No shunting on bubble study

• Only mild atherosclerotic disease on CT angio­gram

• Two ischemic strokes in different arterial territories

• AF on ECG during admission with prior interatrial block

• Retrospective CHA₂DS₂-VASc score of 3 (2 points for age, 1 point for hypertension).

Considered independently, each finding is moderately suggestive of AF, but cumulatively the evidence points to an exceedingly high risk for AF. In the absence of any witnesses to the event, the case author proposes the following sequence of events: thromboembolic stroke to left MCA leading to right-sided hemiplegia and a subsequent fall to the right, causing right-sided head trauma and intracranial hemorrhage.

In hindsight, the author says, AF screening and adequate anticoagulation could likely have prevented the chain of events that appears to have occurred, but there are currently few guidelines regarding screening for AF.

Although aerobic exercise is widely promoted as one of the most important measures people can take to improve their cardiovascular health, data from animals and humans suggest that extensive endurance exercise has potential detrimental effects. In particular, studies have suggested an increased risk of developing AF. The relative prevalence of AF in middle-aged and older adults with extensive endurance training compared with the general age-matched population ranges from 2.3 to 12.8, and is up to 100 times as high in some studies.

The pathophysiological mechanisms for this effect remain speculative. For example, it has been suggested that endurance aerobic exercise may lead to AF through prolonged inflammation with myocardial injury and fibrosis, aberrant autonomic signaling, atrial enlargement with dilation and fibrosis, and increased vagal tone and bradycardia.

Indeed, as described in the British Journal of Sports Medicine, there is a subset of patients with AF younger than 60 who are considered to suffer from "lone" AF, in that physical examination and laboratory tests -- including thyroid function, echocardiography, and exercise stress testing -- do not reveal any cardiovascular disease or other known causal factor.

Data from the 2008 GIRAFA study suggest that 70% of consecutive patients with lone AF had vagal AF; thus, the increased vagal tone induced by endurance sport practice might also explain the appearance of AF.

As reflected in the case report, vagal AF is seen predominantly in males between ages 30 and 50; symptoms usually occur at night, and rarely occur between breakfast and lunch when the sympathetic tone is high, or during exercise or emotional stress. It is commonly triggered during relaxation after stress and is often preceded by bradycardia.

There are no clinical guidelines for considering or screening for AF in middle-aged or older endurance athletes. In 2018, the U.S. Preventive Services Task Force concluded the evidence is inadequate to support routine ECG screening for AF in asymptomatic adults over age 65. Nevertheless, research has shown that subclinical or asymptomatic AF is not a benign condition.

Several recent and ongoing studies using wearable technology to detect AF in the outpatient setting may answer some outstanding questions, the case author notes. While none of these trials -- D₂AF, IDEAL-MD, SCREEN-AF, and STROKESTOP, for example -- include analysis of past or present endurance exercise as a factor in risk stratification or clinical decision-making, they may provide important retrospective data.

AF currently affects an estimated 2.7 million to 6.1 million adults in the United States, and by the year 2050, the prevalence is expected to reach up to 15.9 million, with more than 50% of those affected age 80 or older. Given the aging population, the association of pro­longed endurance exercise and AF warrants further research, and the advent of wearable technology to facilitate outpatient screening for AF may help investigators discover individualized risk factors and help inform guidelines and resource allocation, the case author states.

He warns that endurance exercise is not currently included in such risk assessment tools as CHADS₂ and CHA₂DS₂-VASc, and neither is it studied in current AF detection trials. In fact, despite a growing body of evidence, this clinical correlation is not well-known among clinicians, nor is it described in formal medical education.

The author concludes with the hope that the case report and summary of evidence will help increase awareness and encourage heightened vigilance for AF in asymptomatic older adults with a history of endurance athletic training.

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