A paramedic call is received in the emergency department (ED) reporting a 10-min estimated time of arrival for a 17-year-old male who was found in cardiac arrest following a blow to the chest. The patient has regained spontaneous circulation, and is currently stable and maintaining his own airway. A rhythm strip faxed to the ED prior to the patient's arrival shows ventricular fibrillation, with subsequent conversion to a normal sinus rhythm after defibrillation with 200 joules.

Further questioning of the prehospital personnel reveals a history of witnesses reporting that the patient, a center outfielder for a local baseball team, was trying to catch a baseball when one of his teammates accidentally ran into him, elbowing him in the middle of his chest. The patient immediately dropped to the ground and was unresponsive.

Upon arrival at the ED, the patient reports only mild anterior chest wall pain and denies any substernal chest pain, shortness of breath, palpitations, weakness, or confusion. He states that he has never before fainted. The patient and his mother deny any significant past medical or family history, including any arrhythmias, unexplained sudden deaths, or cardiac structural diseases. He denies having a lower exercise tolerance than his teammates and also denies any smoking, drinking, use of medications, illicit substance abuse, or doping practices.

On physical examination, the primary survey of his airway, breathing, and circulation is unremarkable. The patient has a blood pressure of 130/71 mm Hg and a heart rate of 106 bpm, with a normal rhythm. The respirations are 28-30 breaths/min. The lungs are clear to auscultation bilaterally, and the cardiac examination reveals a regular rate, with normal S1 and S2 heart sounds and no clicks, gallops, rubs, or murmurs. The abdominal and neurologic examinations are unremarkable.
A 12-lead electrocardiogram (ECG) is obtained that reveals sinus tachycardia at a rate of 110 bpm, with mild right-axis deviation. The QRS complex, QT interval, ST/T waves, and P waves are all noted to be normal. A portable, upright chest radiograph shows somewhat underaerated lungs but no signs of fractures, widening of the mediastinum, cardiomegaly, or hemopneumothorax.

What is the likely pathophysiology that led to the cardiac arrest?

very intersting case... so i did my research and i hope the result will be useful..
Commotio Cordis

sudden death in athletes without antecedent heart disease occur as a result of blunt, nonpenetrating, and innocent-appearing blows to the chest that produce ventrictular fibrillation unassociated with structural injury to the ribs, sternum, or heart ..
this is one of the common causes of death among athelets in the fields speciallly children and adolecsent bcoz their chest walls are compliant and transmit the blow easily to the heart .

in anmal models they found that the blow should be directly on the heart and occur within 15 to 30 msec before the peak of the t wave to ellicit VF.
i hope this was helpful ..

excellent Besma, and they also found out that if the blow to the heart was during depolarization [QRS] it will cause transient complete heart block.

The suggested mechanism behind it is a sudden increase in intracardiac pressure.

thanks for this i did not know that such thing exists