Out-of-Hospital Cardiac Arrests during Mass-Participation Endurance Events: A Case Series

Abstract

Introduction

Mass-participation endurance events take place throughout the United Kingdom. Although out-of-hospital cardiac arrests (OHCAs) occur during these events, little is known about them. This case series aims to describe the number, type, etiology, and outcome of OHCAs treated by a UK-based specialist sports medicine provider over a period of 8 y.

Methods

The medical records of a UK-based sports medicine provider were reviewed from 2014 to 2022. Anonymized information from OHCAs during this time was recorded. This included type of event, patient demographics, details of OHCA, and patient outcomes.

Results

Ten OHCAs were identified during the course of 110 sporting events. These included the cases of 9 participants and 1 spectator. Return of spontaneous circulation (ROSC) was achieved on-site in all patients. Eight survived beyond 24 h and achieved a full neurological recovery. Seventy percent of these patients achieved ROSC within 4 min of cardiopulmonary resuscitation being initiated. The 2 patients who died both presented with a nonshockable rhythm.

Conclusions

OHCAs during mass-participation endurance events are rare. However, medical providers must be prepared to respond promptly. Quick interventions can result in a full neurological recovery.

Introduction

Many mass-participation endurance events take place every year throughout the United Kingdom. These events range from short walks to multiday ultramarathons, open water swims, and cycle races to triathlons and obstacle courses. These appear to be growing in number.^1,2

Out-of-hospital cardiac arrests (OHCAs) are known to occur at sporting events. These often attract a great deal of media attention since participants are commonly presumed to be young, fit, and healthy. ^{3 -5} In the London Marathon, there is an estimated death rate of 1 in 80,000 finishers. ⁶ For triathlons, the incidence of OHCAs in the United States of America is estimated at 1.74 per 100,000 participants. ² A study of British Triathlon–sanctioned events found that there were 0.5 triathlon-related deaths per 100,000 participants during the study period. ⁷

In younger adults (aged ≤35 y), the predominant cause of OHCAs in sports has been found to be primary arrhythmic or structural abnormality (such as hypertrophic cardiomyopathy). ⁸ In contrast, in older patients (aged ≥35 y), the majority of OHCAs are secondary to ischemic events.^2,8,9 However, the majority of these patients have no known cardiac disease prior to their OHCA. ⁹

One US prospective study has shown that high rates of survival to hospital discharge can be achieved with prompt defibrillation in OHCAs that occur during sporting events. ¹⁰ Indeed, patients who have an OHCA during a sports activity may have an up to 8 times higher survival rate compared to that of the baseline population.^11,12 However, we are not aware of any research that specifically looks at the experience of UK-based specialist sports medicine providers managing OHCA. Therefore, the aim of this case series is to describe the number, type, etiology, and outcome of the OHCAs seen by one specialist UK-based sports medical event provider and to gain insight into the way these patients were managed.

Methods

The UK-based sports medicine event company (SportsMedics Ltd) is involved in providing medical cover for a wide range of amateur and professional sporting events, including obstacle-based runs, 10-km runs, triathlons (over a variety of distances), and marathons. UK Resuscitation Council guidelines for advanced life support are followed by the company. ¹³ Full advanced life support equipment is available, alongside automated external defibrillators at various points throughout the courses to ensure a quick response time. Many of the clinicians have professional prehospital experience, for example, working for a UK air ambulance or as a team physician. All have suitable qualifications to ensure a high level of care.

The medical records of the UK-based sports medicine event company were reviewed from 2014 to 2022 for any OHCAs, incorporating 110 events and over 1 million participants. Anonymous data relating to patients who experienced OHCAs at mass-participation endurance events were extracted. Data extracted related to the type of event, age, sex, the cardiac arrest, time to return of spontaneous circulation (ROSC), and follow-up data. Although no formal ethical approval was required, the study was registered with the SportsMedics Ltd Research and Audit Team.

Results

Over the course of the study, 10 OHCAs were identified; 9 occurred in participants and 1 in a spectator. For all patients, ROSC was achieved on-site. Two patients did not survive beyond 24 h. The remaining 8 patients achieved full neurological recovery. A summary of demographic and cardiac arrest data can be found in Table 1.

Table 1

Summary of out-of-hospital cardiac arrest data in mass-participation endurance sporting events

Patient	Age (y)	Sex	Event	Comorbidities known prior to event	Initial presenting rhythm	CPR performed	No. of adrenaline doses	No. of shocks	Amiodarone administered	Time to ROSC after commencement of CPR (min)	Hospital diagnosis/treatment	Follow-up
1	47	Male	Obstacle	Nil	Shockable	Yes	0	1	No	2	Arrhythmia—ICD inserted	Full neurological recovery
2	49	Male	Obstacle	Nil	Shockable	Yes	1	2	No	6	PCI	Full neurological recovery
3	45	Male	10 km	Nil	Shockable	Yes	0	1	No	3	PCI	Full neurological recovery
4	53	Male	10 km	Nil	Nonshockable	Yes	0	0	No	2	PCI	Full neurological recovery
5	46	Male	Obstacle	Nil	Shockable	Yes	1	3	Yes	51	Brugada and STEMI (PCI performed)	Full neurological recovery
6	51	Female	Triathlon (run stage)	Asthma	Shockable	Yes	0	1	No	3	PCI	Full neurological recovery
7	69	Male	Triathlon (run stage)	Nil	Shockable	Yes	1	3	Yes	5	PCI	Full neurological recovery
8	52	Female	Triathlon (swim stage)	Nil	Nonshockable	Yes	7	0	No	45	STEMI	Died
9	54	Male	10 km	3 previous cardiac arrests—multiple cardiac stents	Shockable	Yes	0	1	No	3	PCI	Full neurological recovery
10	56	Male	Triathlon (swim stage)	Nil	Nonshockable	Yes	5	0	Yes	30	Nil cause identified (no postmortem data available)	Died

CPR; cardiopulmonary resuscitation; ICD, implantable cardiac defibrillator; PCI, percutaneous coronary intervention; ROSC, return of spontaneous circulation; STEMI, ST-elevation myocardial infarction.

The time to ROSC, the initial rhythm, and the number of doses of adrenaline make the 2 patients who died significant outliers compared with those who survived with neurological integrity. One of the nonsurvivors was thought to have had an ST-elevation myocardial infarction, while no cause was identified for the other. Among the survivors, the maximum adrenaline administered was 1 dose of 10 mL 1:10,000 (1 mg).

Discussion

This study describes for the first time OHCAs that have taken place during mass-participation endurance events in the United Kingdom. In 100% of the patients described in this series, ROSC was achieved, with a high overall survival rate of 80%. All patients who survived achieved full neurological recovery.

The survival rate is similar to that seen in OHCA during sports in other studies where immediate defibrillation was available ¹⁰ but significantly higher than that in other studies.^8,11,12 The recognition of OHCA in the case series was prompt, with both medical and event staff quickly identifying these patients. The ability to swiftly identify OHCA has previously been highlighted as key to achieving good outcomes.^14,15 The availability of highly trained staff throughout the course and good communication between event and medical staff to identify these patients are important and allow resuscitation to be commenced with the correct equipment quickly, including early defibrillation as appropriate. The 100% survival seen in those who achieved ROSC within 5 min is consistent with the literature. ¹⁶ It is also in line with the chain of survival and UK Resuscitation Council guidelines. ¹³

The 2 patients who died presented during the swim leg of the triathlon, and both presented with a nonshockable rhythm. Previous studies have found that deaths during triathlons are more likely to occur during the swim leg.^2,7,17,18 One study reported that drowning was often declared as the cause of death in these patients, although the majority had underlying cardiovascular disease on autopsy. ¹⁷ Another UK-based study found that cardiovascular disease contributed to 3 of 5 triathlete deaths. ⁷ Various theories exist as to why OHCA is more likely in the swim leg, including the need to acclimatize to water exposure quickly, an increase in myocardial oxygen demand, and the early catecholamine peak that may occur and trigger arrhythmias.^2,7,19 Swim-induced pulmonary edema (also known as immersion pulmonary edema) may also be a concern, although the evidence for this is low.^7,18,20 There may even be a conflict between the sympathetic nervous system, with anxiety and anticipation at the start of the swim leg, and the parasympathetic activation of the cold swim, triggering more cardiac arrhythmias. ⁷ In addition, there may be difficulties in extracting patients who have an OHCA while swimming, with guidelines suggesting a medical post should be specifically at the swim point with sufficient staff available.^19,21 Further research is required into this, and event organizers should be aware of this high-risk area.

Limitations

This is a retrospective qualitative study of a single UK-based sports medicine provider and is therefore only a small representation of the true picture of OHCA during mass-participation endurance events. Information extracted is based on the medical notes provided and was not originally intended for research purposes. Omissions were therefore present.

It was not possible to identify the exact time at which the cardiac arrest occurred. This made it impossible to determine the exact time from cardiac arrest to cardiopulmonary resuscitation being initiated and from cardiac arrest to defibrillation. Both of these elements are known to be key factors for patient survival.

Finally, only limited medical information following the cardiac arrest was available. Whether patients returned to athletic activity following the incident and the effects on their long-term health are unclear.

Conclusions

Participants in mass-participation endurance sporting events are at risk of OHCA. However, good outcomes are possible when a well-trained medical team focuses on delivering prompt and effective treatment.