What Caused Damar Hamlin's Cardiac Arrest?

Authored by: Venkat Rao

A short answer is, ‘we do not know’. But a nuanced answer is a bit more troublesome.

Here is what happened on January 3, 2023, at the NFL game between Buffalo Bills vs. Cincinnati Bengals. Associated Press reported that Buffalo Bills safety Damar Hamlin suffered a cardiac arrest after making a tackle and collapsed on the field which resulted in NFL suspend the Monday night’s game with much of the news diverted from the pivotal game to the petrifying sight of a fallen young, healthy athlete.

According to the AP report, Hamlin was hurt while tackling Bengals receiver Tee Higgins, wrapping his arms around Higgins to drag him down. Hamlin quickly got back on his feet, but immediately fell backwards and crashed on the ground and remained motionless for 19 minutes when emergency responders administered CPR in the field and used automated external defibrillator to resuscitate his heartbeat. It was a scary sight.

NFL players are closely monitored on vital health status and go through routine physical checkups.

NFL medical exam processes are lengthy and comprehensive involving very detailed internal medical examination and orthopedic examination. Players are evaluated by a team of physicians for heart, kidney, lung and liver health that includes EKG and stress tests for their heart to ensure the player is in an excellent physical condition to participate in the NFL games. Hence, in the absence of more information on his health, it is safe to assume Hamlin was in great physical condition.

Was it Commotio Cordis? A noted cardiologist suggested Hamlin suffered from commotio cordis, a rare but dangerous injury to the heart that causes cardiac arrest, and in some cases, death. Although most cardiac arrest involve pre-existing health condition, commotio carditis could result due to a blow to the heart and happens exactly within a 30-millisecond window. Hamlin took the hit on the chest and fell, rose up with arrhythmia (irregular heart beat) and immediately collapsed again suggestive of commotio cordis, according to the cardiologist. Nonetheless, commotio cordis occurs when a direct, forceful blow hits an unprotected heart. Football players are required to wear multiple protective padding to protect chest. Padding diffuses the energy of a direct blow to the chest region.

The National Operating Committee on Standards for Athletic Equipment (NOCSAE) recently established, in January 2017, performance standards for chest protection specifically for commotio cordis. In January 2017, NOCSAE officially finalized the world’s first performance standard for chest protection from commotio cordis. Two versions of this standard have been developed for baseball and lacrosse and both become effective in July 2018. The various sport governing bodies may make their own decision whether to include compliance with these standards in their rules of play and when those rule changes will become effective.

NFL requires players wear shoulder pads, hip pads, thigh pads and knee pads, but is less clear about chest protectors. According to a New York Times report, the general trend among NFL players is towards wearing less protective padding, shedding all arm, hip, thigh and knee pads. Excess padding is considered by the players as a sign of weakness, lack of confidence and fear, the report says of the current trend in using protective gears in NFL games. It is unclear if Hamlin was wearing a chest padding specifically created to protect players from commotio cordis when playing the game that night.

There have been instances in the past of cardiac deaths in sports, either due to a pre-existing heart condition or drug use. This does not apply to commotio cordis which manifests instantly due to a chest injury and not because of a pre-existing condition. It is safe to assume a young and energetic NFL player like Hamlin is in top physical condition when the incident happened.

A detailed review published by the National Institute of Health attributed sports-related deaths mostly due to cardiomyopathy or arrhythmia in young adults. Other heart conditions such as myocarditis could result in sudden cardiac death as well, but they seldom occur suddenly. Researchers reviewed a total of 19,740 autopsies comprised of 12,395 subjects in the age group of 18-65 years and 385 children in the 7-17 years. There were 201 sports-related adult deaths at an incidence rate of 0.76-1.49 per 100,000 participant-years. Deaths were mostly due to coronary artery disease in adults and cardiomyopathy or arrhythmia in children. Although sudden cardiac arrest is a rare in young athletes, recommendation from medical professionals was to make automated external defibrillators in public spaces as part of preparedness and response to prevent athlete fatalities. Hamlin suffered ventricular arrhythmia requiring use of automated external defibrillator together with CRP before he was transported to a hospital.

Was it Acute Myocarditis the cause of Hamlin’s cardiac arrest?

Soon after the unfortunate January 3 incident, several unfounded claims and unreliable theories started appearing in the media and social networks that COVID-19 vaccination caused Hamlin’s cardiac arrest. An equally vehement counter-response appeared in the media that COVID-19 vaccines did not cause the cardiac arrest. Both claims and counter-claims need a careful review.

Acute viral myocarditis in young adults is a leading cause of sudden cardiac death in young adults less than 30 years age and its prevalence in the United States according to 2021 data is approximately 16.2 per 100,000 population.

According to the August 2022 British public health report, the risk of myocarditis was substantially higher after COVID-19 infection than after the first dose of the vaccine among the 43 million people in England who received at least one COVID-19 vaccine. The study reports, the risk of COVID-19 vaccine-associated myocarditis was higher in young men 40 years age or less after the first dose of an mRNA vaccine, or after a second dose of any of the three vaccine currently available in the United Kingdom.

According to the CDC’s September 2022 report, myocarditis and pericarditis were reported after COVID-19 vaccination among adolescent and young adult males within several days after Pfizer-BioNTech or Moderna mRNA COVID-19 vaccines. Myocarditis was reported after the second vaccine doze and within a week of vaccination. Although much of the early evidence were merely associative lacking causality, it was in September 2021, two clinical cases of myocarditis were reliably confirmed after COVID-19 vaccination. Although the medical research team reporting the study results did not establish a causal link there were no other intervening risk factors established by PCR assays or serologic evidence for presence of some other trigger to induce acute myocarditis.

A similar study in the United States on 1,626 cases of myocarditis in the FDA’s Vaccine Adverse Event Reporting System (VAERS), a national passive reporting network, reported myocarditis incidence reports within 7 days after vaccination at levels exceeding the baseline rates across multiple age and sex groups. The incident rates of myocarditis were highest after the second vaccination in adolescent males aged between 12-15 years at 71 cases per million doses of Pfizer vaccine, 106 per million doses Pfizer’s vaccine for young men aged 16-17 years and 52-56 cases per million doses of Moderna vaccine in men aged 18-24 years.

According to the FDA's VAERS data, between December 14, 2020 and August 31, 2021 little over 192 million individuals older than 12 years age received a total of 354 million mRNA-based COVID-19 vaccines. During this period VAERS received 1,991 reports of myocarditis after receiving at least one dose of the vaccine of which 73% of the reported cases of myocarditis were in men younger than 30 years age. A total of 82% of the reported cases were after receiving the second vaccine dose. Symptoms commonly reported by young men 30 years or younger in the VAERS system are chest pain, pressure, or discomfort (89%) and shortness of breath (30%).

A detailed study by a Danish team on myocarditis-induced sudden cardiac death concluded, myocarditis is vastly underreported in medical records and not recorded as the cause of death in death certificates. This study concluded nearly 6% of all autopsied sudden cardiac deaths was caused by myocarditis. Young men were at a higher risk compared when to women towards myocarditis-induced sudden cardiac death.

According to another related analysis of large medical datasets, cardiac arrhythmia or conduction system problems in COVID-19 patients may be apparent, and consistent with a large US medical registry report of the 31,000 patients hospitalized with COVID-19, 1,674 (5.4%) manifesting new onset of atrial fibrillation. In another separate meta-analysis of 19 observational (clinical) studies of 21,653 patients hospitalized with COVID-19, the incidence rate of atrial fibrillation was even higher at 11 percent.

More recently, several studies established probable causal relationship between Pfizer’s mRNA vaccine (BNT162b2) and Moderna’s (mRNA-1273). COVID-19 vaccines and myocarditis occur mostly in children and young adults. It is relevant to point out that scientific literature is replete with studies on myocarditis as a major factor for sudden, unexpected deaths in young adults less than 40-years age and attributable to up to 20% of those deaths. These studies conclude that in some cases vaccine-induced myocarditis leading to other adverse cardiovascular events in young adults as not a theoretical deduction, and merits further serious investigation.

Hamlin’s miraculous recovery is a great news, but we will not know in affirmative what caused his cardiac arrest on January 3, while playing the NFL game. Did a sudden blow to his chest induced commotio cordis, or a generally underdiagnosed myocarditis caused the cardiac arrest? It is possible that both risk factors were in play—myocarditis condition, a generally underdiagnosed condition, introduced an additional risk factor leading to commotio cordis while playing the game—when hit with the direct impact on his chest precipitating cardiac arrest.

So, what caused Hamlin’s cardiac arrest? Based on a balanced examination of available information, the jury is still out.