Understanding Sudden Cardiac Death

Sudden cardiac death accounts for almost half of all cardiovascular deaths and 10 - 20% of all deaths in general1.

In my clinical practice, this typically presents as a concerned middle age executive sitting across from me in clinic because a friend or colleague died suddenly at home or while exercising.

I’m 58, and a close friend collapsed and died last month. It was a heart attack. I want to make sure that isn’t me in 6 months.

As a clinical consultation, this scenario is not unusual.

In general, these individuals who die suddenly typically all have underlying coronary artery disease. This population is very different from those who die suddenly at much younger ages with conditions such as hypertrophic cardiomyopathy or arrhythmia disorders. These conditions are typically categorised as non-ischemic heart diseases and account for only 20% of sudden cardiac deaths2. Think professional soccer player collapsing suddenly on the pitch.

80% of sudden cardiac deaths are a result of coronary artery disease.

As discussed previously, heart attacks are caused by the rupture of a plaque in the coronary artery, causing a clot to form and block the artery. In some individuals, this heart attack will be fatal and lead to sudden cardiac death.

The plaque responsible for this event is often not severely narrowed, which is why exercise stress tests often fail to detect these patients and why they usually have no symptoms before their first event3.

Recent research has added some complexity to the idea that these sudden cardiac deaths are all related to an acute plaque rupture.

In Finland, all sudden cardiac death patients undergo an autopsy, which provides an amazing opportunity to examine the arteries of these patients. The assumption based on prior research is that most of these patients would show evidence of an acute plaque rupture consistent with a heart attack that likely resulted in a fatal heart rhythm.

This is not what they found.

Plaque rupture or plaque haemorrhage was found in only 48% of patients.

Significant (>75%) but stable plaque (No rupture or bleed) was found in 52% of patients.

Plaque histology and myocardial disease in sudden coronary death: the Fingesture study, European Heart Journal, 2022

This means that over half of the patients who died suddenly had a significant amount of plaque in their arteries, but no clot formed inside the artery and blocked blood flow to the muscle.

The presumption (and it is only that) is that these patients died because there was spasm or a temporary reduction in blood flow down the artery which caused a fatal heart rhythm. Alternatively, these patients may have had a fatal heart rhythm from scar tissue in the heart muscle. This later explanation does not require the plaque in the artery to rupture and would account for the ‘stable plaque’.

Examples of various culprit lesion morphologies in histological analysis with the Masson-Trichrome stain: (A) stable plaque, (B) intraplaque haemorrhage, and (C) plaque rupture with thrombosis (1).

What is crucial to point out is that 78% of patients had heart muscle enlargement (hypertrophy), and 93% had evidence of fibrosis/scarring.

Only 2.7% of patients had no evidence of heart enlargement or scarring.

The causes of heart enlargement and scarring vary, but the leading cause is usually high blood pressure.

The critical takeaway, however, is that ALL of these patients had a significant burden of coronary artery disease, and almost ALL of these patients had evidence of either heart muscle enlargement or scarring likely due to cardiovascular risk factors.

For patients in this age group, mid 60’s, the key factor driving their risk of sudden cardiac death was coronary artery disease and the risk factors typically associated with it.

To be 100% clear.

There are other causes of sudden cardiac death, but the lion’s share are a result of coronary artery disease.

Relationship To Exercise

The story that we often hear is about someone dying suddenly when out running. The Finnish study cited 18% of sudden cardiac deaths occurred during physical activity.

But as always, the devil is in the detail.

The risk of sudden cardiac death increases during vigorous physical activity, primarily in those with underlying coronary artery disease.

But the risk is 10-fold higher in those who are not regular exercisers4.

Even more importantly, the risk of sudden cardiac death in regular exercisers is 40% LESS compared to those who are primarily sedentary5.

In general, far more people will die from sudden cardiac death because they don’t exercise rather than because they do.

The key takeaway is to exercise regularly but build up your fitness base slowly. Most people who start running, for example, usually run way too fast for their current aerobic fitness level. Most people would benefit considerably by simply slowing down.

Before working with a dedicated running coach, I had no idea I was training in all the wrong zones. Spending more time in the appropriate training zones improved my performance considerably and made my training significantly more enjoyable.

Win. Win.

What if the worst happens?

Sudden cardiac death is bad.

But it is survivable.

It was always the thing on a patient’s medical records that took me by surprise; a history of death.

And yet they are still here.

Surviving sudden cardiac death is a multifactorial issue, but early access to defibrillation typically makes the biggest difference. Those with sudden cardiac arrest who had early access to defibrillation with an AED before the arrival of emergency services were over six times more likely to survive compared to those that didn’t have early defibrillation6.

With all this knowledge, here is the key principle to take away:

  1. Avoid cardiovascular risk factors. Fewer risk factors, less disease, less chance of sudden cardiac death.

  2. Exercise. But if you are new to it, go easy. Get advice.

  3. Public defibrillators and CPR save lives. Learn both. Knowing these skills won’t save you, but they very well might save someone else.


Plaque histology and myocardial disease in sudden coronary death: the Fingesture study, European Heart Journal, 2022;, ehac533,


Plaque histology and myocardial disease in sudden coronary death: the Fingesture study, European Heart Journal, 2022;, ehac533,


From Detecting the Vulnerable Plaque to Managing the Vulnerable Patient: JACC State-of-the-Art Review. J Am Coll Cardiol. 2019 Sep 24;74(12):1582-1593.


The incidence of primary cardiac arrest during vigorous exercise. N Engl J Med. 1984 Oct 4;311(14):874-7.


The incidence of primary cardiac arrest during vigorous exercise. N Engl J Med. 1984 Oct 4;311(14):874-7.


Sudden Cardiac Death in Athletes. Methodist Debakey Cardiovasc J. 2016 Apr-Jun;12(2):76-80.

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