Suppose a proportion of what we call sudden cardiac death is not primarily cardiac.
That question stayed with me after my recent interview with Dr Dov Gebien. I had invited him to discuss his work on sudden infant death syndrome and his hypothesis that, in some infants, the terminal event may involve sustained contraction or dysfunction of the diaphragm.
I approached the discussion as a specific question about SIDS. But as I listened to the proposed mechanism, I realised the implications could extend well beyond infancy. If a diaphragm can become inflamed, fatigued or mechanically locked in an infant, I have to ask whether the same thing could occur in an adult. More specifically, whether it could explain a small but important subgroup of sudden deaths during sleep, particularly when the heart appears structurally normal at autopsy.
I am not presenting this as established fact. I am showing how I arrived at a hypothesis that I believe deserves proper investigation.
The Label May Be Hiding an Assumption
I think the terminology itself creates a blind spot.
When a young person dies suddenly and no obvious cause is found, the event is often placed within the category of sudden cardiac death or sudden arrhythmic death syndrome. That wording immediately directs attention towards the heart.
I then assume that an undetected electrical disturbance—perhaps ventricular fibrillation—was responsible. That may often be correct. A person can have an inherited channelopathy or electrical instability without visible structural disease at autopsy. I do not dispute that.
But there is an important difference between saying an arrhythmia is possible and saying it has been demonstrated.
When no structural heart disease is found, no rhythm was recorded and no witness observed the physiological sequence, I am looking at an inferred mechanism. The person died suddenly, the heart stopped, and the event was therefore classified as cardiac.
The difficulty is that every terminal event eventually involves the heart stopping.
That does not tell me what failed first.
The Australian Data Raised the First Concern
I looked at prospective Australian and New Zealand data on sudden cardiac death among children and young adults.
The largest diagnostic category was unexplained death.
Other cases had recognisable pathology. Coronary disease, myocarditis, hypertrophic cardiomyopathy, dilated cardiomyopathy and arrhythmogenic cardiomyopathy provide plausible cardiac explanations. Aortic dissection provides a clear vascular one.
But the unexplained category is different.
These were predominantly young people, many of whom underwent detailed postmortem examination. Despite that, no clear cause was identified. Yet the deaths remained framed as cardiac.
What caught my attention was the proportion occurring during sleep. Sudden collapse during exercise fits naturally with certain cardiac mechanisms. Exertion increases heart rate, sympathetic drive and myocardial demand. In someone with an arrhythmogenic substrate, that stress may expose the problem.
