Syncope refers to the sudden loss of consciousness due to temporary loss of oxygen supply to the brain, most commonly as a result of loss of cerebral perfusion.
General causes of syncope include:
Sudden change in heart rate (bradycardia, tachycardia)
Obstruction to blood flow (eg. valvular stenosis, pulmonary hypertension, obstructive HCM, cardiac tamponade)
Reduced preload (eg. blood loss, dehydration, hypotensive drugs)
Right to left shunt (eg. Tetralogy of Fallot)
Given the findings on physical examination, sudden change in heart rate, specifically bradycardia (long pauses), is likely responsible for the syncope in this case.
The arrhythmia has been characterized as periods of profound bradycardia and tachycardia on auscultation. An electrocardiogram is necessary to specifically determine the arrhythmia present.