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Background
The dive reflex was originally observed in aquatic animals, specifically seals. It is a cardiovascular reflex, mediated through increased vagal tone, that results in more efficient oxygen utilisation and a slower heart rate while ensuring adequate cerebral perfusion (through maintenance of mean arterial pressure) and redistribution of core blood flow. 1-3 When precipitated in humans by immersion in cold water, the human dive reflex (HDR) primarily results in a reflex bradycardia response. 4 5 This bradycardia, and an associated increase in myocardial refractoriness, can be harnessed in a simple and non-invasive manoeuvre for the termination of paroxysmal supraventricular tachycardia (PSVT).
The HDR manoeuvre in humans has resulted from applying the concept of cold induced bradycardia (stimulation of thermoregulatory sensors in the skin triggering increased vagal tone) to the reversion of PSVT through prolonged myocardial refractoriness. 1-3 Studies have demonstrated that immersion of the face only is sufficient to elicit this reflex in human subjects. 1 2 6 7 Hence the simplicity of facial immersion to elicit the HDR is useful in providing increased vagal tone for PSVT management. Increases in vagal tone above that generated by the HDR alone have been reported when subjects performing the manoeuvre also employed deep inhalation and breath holding, which provoked a mild bradycardia. 1 2 4 6 This is due to stimulation of baroreceptors in the carotid bodies and aortic arch, which triggers an increase in vagal tone (a reflex common to both the Valsalva manoeuvre and the carotid sinus massage techniques 8-10 ). It is likely that the combination of breath holding and cold stimulus provides the HDR with an increased effect for PSVT termination; however, this is yet to be quantified in clinical studies.
Use of the HDR for the reversion of haemodynamically stable PSVT has been advocated since the early 1970s. 1-3 5-9 11-13 However, use of the HDR in the prehospital setting is a relatively recent adaptation from emergency medicine practice, providing a simple management strategy for patients with regular narrow complex tachyarrhythmias.
Although the HDR has gained acceptance for the treatment of PSVT within international resuscitation guidelines, 14-16 a standard approach with maximum effectiveness has not been described. Consequently, this review aims to identify a standardised technique to elicit HDR for the management...