What is commotio cordis?

There is a scene in “Tombstone,” where Doc Holliday and Johnny Ringo berate each other in Latin. After the first exchange, Doc turns to his paramour, Kate Elder and explains, “That’s Latin, darlin’. Apparently, Mister Ringo is an educated man.”

That scene remains one of the most Googled Latin phrases, only recently supplanted by the term “commotio cordis” after the cardiac arrest of Buffalo Bills safety Damar Hamlin on Monday Night Football on Jan. 2, 2023, and subsequent theorizing about what caused his collapse.

Let us hope that EMS professionals are among the educated and not among those Googling it. Commotio cordis is a rare phenomenon, but one every medical professional should know about and understand.

R-on-T phenomenon

Commotio cordis is Latin for “agitation of the heart,” and occurs as a result of a sharp blow to the chest during the heart’s relative refractory period, inducing a mechanical R-on-T phenomenon and resultant ventricular fibrillation (VF) arrest.

When cardiac muscle repolarizes – shifting potassium and sodium ions back to their original places on either side of the cardiac cell membrane – there is a short phase where the heart cannot respond to any other electrical stimulus; there are not enough cells repolarized to propagate an electrical impulse.

This short phase, known as the absolute refractory period, is reflected on the ECG from the end of the QRS complex to the peak of the T wave. That is also the part of the ECG that changes in ischemia or injury patterns like STEMI, because ischemic or injured myocardium tends to remain partially polarized or depolarized – it does not return to baseline.

The relative refractory period extends from the peak of the T wave to the end of the T wave, and during this phase, the myocardium can respond to stimulus, if it is strong enough.

Back in the days when the ACLS textbooks were painstakingly scrawled on papyrus leaves by medical monks, they taught us old medics of this thing called “R-on-T phenomenon.” First described by Smirk in 1949 as “R waves interrupting T waves,” it was postulated that a premature beat – usually a PVC – that fell on or near the preceding T wave could induce polymorphic VT or VF [1,2]. Instructors used this possibility to teach medical providers of the day the supposed danger of mucking about with the heart’s relative refractory period and to justify the prophylactic administration of ventricular antiarrhythmics, such as lidocaine.

Turns out, R-on-T phenomenon isn’t as common as we once thought, there is little evidence to link it to VF or polymorphic VT and, in any case, the cure – lidocaine – was often worse than the disease [3,4].

But absence of evidence does not mean evidence of absence, and it is still plausible that R-on-T phenomenon could induce cardiac arrest. In any case, the treatment is the same: standard AHA protocols for VF arrest.

Cardiac arrest resuscitation

In the case of commotio cordis, this R-on-T phenomenon is mechanically induced by a sharp blow to the chest. The stereotypical commotio cordis victim is the slender pre-adolescent baseball player who takes a line drive in the chest. It doesn’t happen often (less than 30 cases a year), but it happens often enough that there is a stereotypical patient and a national registry to gather data on the phenomenon [5].

In Damar Hamlin’s case, the impact between him and Cincinnati Bengals receiver Tee Higgins didn’t seem all that severe. This is also typical of commotio cordis; it isn’t a matter of kinetic energy, but instead a matter of exquisitely inopportune timing.

In this video of a competitor in a karate tournament, you see a similar phenomenon; a seemingly innocuous counterpunch to the chest, the victim returns to his position and collapses several seconds later.

It takes several seconds for the brain to run out of oxygenated blood after the heart stops; many of you may have personally witnessed a VF arrest and noticed that the victim may have their eyes open and spasmodically breathe in the first few moments of VF arrest. I personally remember a resuscitation when our VF patient was awake and aware of what was going on for the first 20 minutes of the resuscitation. This is apparently a common enough phenomenon that many forward-thinking physicians recommend sedation for those victims who appear to be awake during their cardiac arrest resuscitation.

In any case, on this Monday night, millions of people got to see stellar cardiac resuscitation as it should be performed – on the scene – with a positive result. As I am writing this 72 hours later, Damar Hamlin is awake and holding hands with his family members, neurologically intact.

When laypeople wonder why it took 15 minutes for EMS to load him into the ambulance, correct their ignorance by pointing out that cardiac arrest is usually resuscitated in the field, or not at all [6-11]. And if it’s an EMS professional you know saying that, really correct them. We can’t afford to not know these things.

References

1. Smirk F.H. R waves interrupting t waves. Br Heart J. 1949;11:23-36.
2. Smirk F.H., Palmer D.G. A myocardial syndrome. With particular reference to the occurrence of sudden death and of premature systoles interrupting antecedent t waves. Am J Cardiol. 1960;6:620–629.
3. Engel TR, Meister SG, Frankl WS. The “R-on-T” phenomenon: an update and critical review. Ann Intern Med. 1978 Feb;88(2):221-5. doi: 10.7326/0003-4819-88-2-221. PMID: 75705.
4. Bluzhas J, Lukshiene D, Shlapikiene B, Ragaishis J. Relation between ventricular arrhythmia and sudden cardiac death in patients with acute myocardial infarction: the predictors of ventricular fibrillation. J Am Coll Cardiol. 1986 Jul;8(1 Suppl A):69A-72A. doi: 10.1016/s0735-1097(86)80031-6. PMID: 2423572.
5. Tainter CR, Hughes PG. Commotio cordis. Available at: https://www.ncbi.nlm.nih.gov/books/NBK526014/
6. Sasson C, Hegg AJ, Macy M, Park A, Kellermann A, McNally B; CARES Surveillance Group. Prehospital termination of resuscitation in cases of refractory out-of-hospital cardiac arrest. JAMA. 2008 Sep 24;300(12):1432-8.
7. Bonnin MJ, Pepe PE, Kimball KT, Clark PS Jr. Distinct criteria for termination of resuscitation in the out-of-hospital setting. JAMA. 1993 Sep 22-29;270(12):1457-62.
8. Bachman MW, Williams JG, Myers JB, et al. Duration of prehospital resuscitation for adult out-of-hospital cardiac arrest: Neurologically intact survival approaches overall survival despite extended efforts. Prehosp Emerg Care. 2014;18(1):134–135.
9. Nagao K, Nonogi H, et al, Japanese Circulation Society With Resuscitation Science Study (JCS-ReSS) Group*. Duration of Prehospital Resuscitation Efforts After Out-of-Hospital Cardiac Arrest. Circulation. 2016 Apr 5;133(14):1386-96.
10. Reynolds JC, Grunau BE, Rittenberger JC, Sawyer KN, Kurz MC, Callaway CW. Association Between Duration of Resuscitation and Favorable Outcome After Out-of-Hospital Cardiac Arrest: Implications for Prolonging or Terminating Resuscitation. Circulation. 2016 Dec 20;134(25):2084-2094.
11. Gregers E, Kjærgaard J, Lippert F, Thomsen JH, Køber L, Wanscher M, Hassager C, Søholm H. Refractory out-of-hospital cardiac arrest with ongoing cardiopulmonary resuscitation at hospital arrival - survival and neurological outcome without extracorporeal cardiopulmonary resuscitation. Crit Care. 2018 Sep 29;22(1):242.