Sudden Cardiac Death
Over 100,000 people die from sudden cardiac death annually in the UK. While the majority of deaths are due to coronary heart disease, sudden unexpected cardiac deaths can occur in different age groups. In this article Dr Kevin Jennings reviews the evolving evidence which is enabling us to identify those at greatest risk of sudden cardiac death.
- Most sudden cardiac death is due to coronary artery disease.
- Sudden cardiac death under 30 years of age is usually due to inherited heart disease.
- Autopsy fails to reveal a cause in about 4% of sudden cardiac deaths.
- Relatives of young victims of sudden cardiac death, particularly first-degree relatives, should be investigated as this may identify the cause of victim deaths and allow effective preventative treatment for relatives.
- Autonomic nervous abnormalities identified from heart rate variability can identify those at increased risk of sudden cardiac death.
- Patients with advanced heart disease are at increased risk of sudden cardiac death and this may be prevented by cardiac resynchronisation and defibrillation therapy.
- Drugs recognised as precipitating serious cardiac arrhythmias should be avoided whenever possible.
Declaration of interests: No conflict of interests declared
The majority of the approximately 100,000 sudden cardiac deaths each year in the UK are associated with coronary heart disease, but most sudden deaths in those under 30 years of age are caused by inherited cardiomyopathies and arrhythmias. In those aged 16–64 years, a coroner’s post mortem examination is unable to identify a structural cardiac abnormality in 4·0%. The cause of death is therefore uncertain. These deaths are termed Sudden Arrhythmic Death Syndrome (SADS) or Sudden Unexpected Death Syndrome (SUDS).
Inherited disease and sudden cardiac death
Sudden death can occur in those with structurally normal hearts who have abnormalities of the cardiac ion channels which prevent sodium, calcium and potassium ions, important in regulating cardiac activity, from crossing the cell membranes of cardiac muscle cells appropriately (see Table 1).
These are inherited conditions and the relatives of the victim may therefore be at risk of dying suddenly from potentially reversible disease. Also, it may only be by identifying the abnormality in relatives that the cause of death in the victim might be identified. In one study, 43 families where young adults had died suddenly were investigated; 151 carriers of pre-symptomatic disease were identified, and the likely cause of death of the victim was identified in 17 (40%) of the 43 families studied.1
There are rare, also genetic, conditions associated with structural cardiac disease which have been identified in relatives of a victim, but not detected at post mortem examination (Table 2). This may reflect variable penetrance of these conditions.
Families of victims of sudden cardiac death must be assessed for inherited disease. Histories should be obtained of previous unexplained syncope, family history of sudden death, congenital deafness (Jervill-Lange-Nielson syndrome) and muscle weakness. First-degree relatives should have an ECG, a signal averaged ECG (a computer interrogation of the ECG seeking afterpotentials which are arrhythmogenic), an echocardiogram, a holter monitor and an exercise test. Thereafter some will require additional testing using cardiac magnetic resonance imaging, adenosine provocation (to reveal QT prolongation) and electrophysiological study.
Interventions with, for example, implantable defibrillators can prevent sudden death. The DEBUT study,2 compared implantable defibrillators with beta blockade in a SUDS study. In this study patients with structurally normal hearts who had survived an episode or who had an ECG pattern of SUDS were randomised to either beta blockade or defibrillator therapy. Over a two-year follow up, four died in the medical treatment arm, whilst seven people with defibrillators experienced an event successfully terminated by the device and no patient with a defibrillator died.
The autonomic nervous system and liability to sudden cardiac death
There is accumulating evidence of a close association between abnormalities in the autonomic nervous system and sudden cardiac death. This autonomic imbalance reflects either a relative or absolute decrease in vagal activity or an increase in sympathetic stimulation. One of the measurable manifestations of this is heart rate variability. It has been suggested that low heart rate variability is associated with sudden death in patients with cardiovascular disease. Bigger3