Ectopic pregnancy, described as the extrauterine implantation of a conceptus, is the leading cause of first-trimester maternal deaths in the US. It presents classically as a triad of vaginal bleeding, abdominal pain and amenorrhea but has a low positive predictive value. Ruptured EP will present as lateralized, sudden, severe pain as it did with this patient, and frequently presents with a syncopal or near syncopal episode.  

Ruptured EP will produce unstable vital signs such as hypotension secondary to hypovolemia. The diagnosis may be complicated by a relative bradycardia secondary to vagal stimulation in the presence of a hemoperitoneum. Hemoperitoneum and bradycardia is a phenomenon that has been described for decades but never fully understood. In 1978, Jansen described four cases of acute intraperitoneal bleeding in the pelvis and hypotension accompanied by a relatively normal or bradycardic response (HR<80). Both the hypotension and bradycardia subsequently responded to atropine, suggesting that a parasympathetic vagal reflex was occurring in the presence of rapidly compromising hemodynamics 

It is widely believed that worsening tachycardia is associated with progressive hypovolemic shock and a resultant bradycardia indicates an irreversible state of shock. However, Oberg and Thoren went on further to theorize that bradycardia is in fact a protective mechanism that reflexively stimulates diastolic ventricular filling leading to a bigger stroke volume.

Early recognition and prompt resuscitation is critical in the management of patients with suspected circulatory collapse secondary to ectopic pregnancy. Failure to recognize such a patient in the prehospital or emergency room setting can be potentially life threatening.