Exercise-Associated Collapse: On-the-Field and In-Office Assessment

Introduction

Endurance events continue to be a popular athletic and social outlet for runners of all ages and abilities. In 2016, there were a total of 30,400 distance running events, and the estimated number of finishers of sanctioned running events that year was 16,957,100. It is estimated that approximately 25 of every 1000 finishers will seek medical attention during a marathon with fluctuations seen based on race day conditions and runner experience. Studies demonstrate that 59%–85% of visits to the medical tent during a marathon or ultramarathon are related to exercise-associated collapse (EAC).

It is important to note that there are sometimes conflicting definitions of EAC within the literature. Historically, the term referred to the transient and benign phenomenon where sudden cessation of activity upon completion of an endurance event causes an athlete to become lightheaded due to venous pooling in the lower limbs. In this context, EAC was a diagnosis of exclusion and was applied once other entities had been ruled out. In recent years, the term EAC has often come to stand for the overarching concept of the collapsed athlete and includes all the potential causes on the differential diagnosis list. For the purposes of this chapter, this specific phenomenon of venous pooling will be referred to as exercise-associated postural hypotension (EAPH) and will be discussed in more detail in the following. The term EAC will be used as an umbrella term to describe not only the commonly seen EAPH but also the other possible entities to consider in the collapse of an athlete. Refer to Table 4.1 for a quick reference of the exercise-associated conditions discussed in this chapter.

A critical question while evaluating the collapsed runner is whether the EAC occurred during or after the race. Any collapse in the midst of racing is ominous and should prompt immediate resuscitation and transfer to a hospital for a thorough evaluation that will certainly include a cardiac workup. If the collapse is after one finishes, and is without mental status change, it is often the result of EAPH and should respond to conservative measures such as elevation of the legs and oral rehydration in the medical tent. However, it is imperative that healthcare providers understand the other potential causes of an EAC to ensure expedient and appropriate care both on race day and when seeing runners for follow-up in the office. This chapter will highlight the approach to the runner with EAC from race day through follow-up with their primary medical providers.

On-the-Field Assessment—Exercise-Associated Collapse

Medical conditions that present to the finish areas of endurance races are relatively well defined. Fluctuations in presenting symptoms can occur based on the environmental conditions that exist on race day. It is not uncommon to see both heat and cold illness during the same race, so providers must be prepared for all comers. One must also understand that there is an inherent risk of cardiac fatality based solely on the law of averages due to numbers of participants in any type of mass participation event. The literature reports sudden cardiac arrest rates to be approximately 1 in 57,000 to 1 in 100,000 participants in the marathon setting with older males being the most at risk. Events typically occur in the last 4 miles of a race, and mortality with no intervention is greater than 95%. Remember that a common presenting sign of cardiac arrest is seizure-like activity; thus, any collapsed runner with seizure-like activity should be presumed to have a cardiac source for the collapse until ruled out (i.e., immediately begin clinical assessment of behavior instead of waiting for a potential seizure to cease). Initial treatment of a cardiac arrest is immediate defibrillation (within 3 minutes of arrest) and can produce survival rates in the range of 67%–74%. Therefore, it is imperative that emergency planning accounts for this potential risk. Although physicians should be prepared to evaluate and treat all causes of collapse in the athlete, approximately 60% of the time collapse after completion of a race is secondary to a benign entity known as EAPH.

EAPH is a normal physiologic consequence of prolonged exercise. During competition, runners increase their cardiac output and stroke volume, as their pumped blood is shunted to the lower limb muscles. As a result, peripheral vascular resistance decreases during exercise to promote delivery of blood to the working muscles. In response, the skeletal muscles continuously contract, functioning as a “second heart” to promote venous return to the heart from the dilated lower limb vasculature. Once activity stops, however, so do these contractions, leading to diminished venous return to the central circulation and blood pooling. This results in hypotension, lightheadedness, dizziness, or syncope in a conscious runner who is subsequently unable to stand or walk unaided.

This phenomenon is not unique to novice participants but can be seen in the elite runner as well. With exercise conditioning, an athlete's heart will undergo eccentric hypertrophy and left ventricular hypertrophy in response to the increased demand. To supply the required increase in cardiac output, stroke volume increases to properly oxygenate the working muscles. Conditioned runners have an additional hurdle in that their increased vagal tone results in a naturally lower resting heart rate, which can contribute to EAPH.

For these reasons, all endurance athletes are encouraged to keep moving after crossing the finish line rather than coming to a complete stop. For example, many marathons across the United States have developed a “27th mile” where the athletes are coaxed to walk through a finish chute, collecting water and electrolyte replacement along the way until they can exit the race and rejoin their families.

Although common, EAPH is considered a diagnosis of exclusion, and so the physician must first rule out other potentially life-threatening causes of EAC (see Fig. 4.1 ). The runner should be quickly evaluated for other commonly seen conditions, such as cardiac abnormalities, exertional heat stroke (EHS), and exercise-associated hyponatremia (EAH) that can also present to a race medical tent.

Medical Tent Approach