Key result
Simulated diving elicits a ~14 bpm blunted tachycardic response in syncopal asthmatics versus controls, suggesting autonomic dysfunction.
Why the study?
Sudden death in some asthmatics is not preceded by obvious worsening of symptoms, raising the hypothesis that autonomic dysregulation may cause susceptibility to fatal cardiac arrhythmias.
Does a simulated diving reflex reveal autonomic dysregulation in asthmatics with a history of syncope compared to controls?
Does a simulated diving reflex reveal autonomic dysregulation in asthmatics with a history of syncope compared to controls?
Asthmatics with a history of syncope exhibit a marked bradycardic response to a simulated diving reflex, suggesting autonomic dysfunction that may predispose them to sudden cardiac death.
May warrant autonomic testing in syncopal asthmatics; hypothesis-generating for preventing sudden cardiac death in this group.
Background Epidemiological evidence and post-mortem case series suggest a variety of pathophysiological mechanisms underlying mortality in asthma. In some asthmatics sudden death is not preceded by obvious worsening of asthma symptoms. Aim We hypothesize that this group may be susceptible to fatal cardiac arrhythmias due to a dysregulation of autonomic function. Methods We investigated autonomic function in 2 groups of asthmatics; those with a history of syncope during exacerbations (n=4) and those without (n=10). These were compared with non-asthmatic controls (n=10). The simulated diving reflex was chosen as it has known reproducible effects on cardiovascular autonomic function. Measurements obtained included heart rate, blood pressure and electrocardiograph monitoring preceding and throughout the simulated dive. Results Normal subjects as well as non-syncopal asthmatics responded in a typical fashion to a simulated dive with initial tachycardia followed by bradycardia (between group difference -1.42bpm, p=NS). Compared to controls, syncopal asthmatics demonstrated an attenuated tachycardic response (-14.32bpm, p=0.03). Dive-induced AUC of change in heart rate was significantly different in syncopal asthmatics compared to controls (p=0.04), demonstrating a marked bradycardia. QTc interval estimation produced similar significant changes. No between group blood pressure differences were noted. Conclusion We demonstrate a relative bradycardic response to a simulated diving reflex in syncopal asthmatics suggesting an autonomic dysfunction, which may predispose to asystolic cardiac arrest. This mode of death in acute asthma is supported by case reports and epidemiological findings but has previously been unrecognized as a mechanism.
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Morjaria et al. (2014) studied this question. Syncopal asthmatics exhibited an attenuated tachycardic response (-14.32 bpm, p=0.03) to a simulated dive compared to controls, suggesting autonomic dysfunction predisposing to cardiac arrest.
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