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Upon initial cardiac rhythm monitoring following OHCA, a patient may present in either a shockable 
rhythm (ventricular fibrillation or ventricular tachycardia) or non-shockable rhythm (asystole or 
idioventricular/pulseless electrical activity [PEA]). Treatment and prognosis depend on presenting rhythm, 
with significantly better survival rates among patients presenting with a shockable rhythm compared to 
those with a non-shockable rhythm (29.9% vs 6.3%, p<.0001).
18.5% of patients presented with an initial shockable rhythm of ventricular fibrillation (VF) or ventricular 
tachycardia (VT), while 81.5% of patients presented in an unshockable rhythm, with asystole being the 
most common (50.1%). The presenting rhythm differed markedly by arrest witness status, with bystander 
witnessed patients being much more likely to present in a shockable rhythm compared to unwitnessed 
patients (29% vs 11%, respectively; p<.0001) (Figure 9).
Initial Rhythm
Figure 9. Presenting arrest rhythm by arrest witness status.

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