Cardiac arrhythmias and sudden death

Sudden death is one of the most important health problems in western countries. It affects approximately 1/1000 inhabitants/year. The principal cause of sudden death is the occurrence of malignant cardiac arrhythmias, which result in the loss of contraction of the heart with subsequent lack of blood supply to vital organs like the brain. The immediate consequence is loss of conscience, and if the arrhythmia persists for more than 5 minutes, the patient dies.

The only way to avoid the fatal outcome is to restore the normal cardiac rhythm by means of an electrical cardioversion or in some cases by using a pacemaker.

The patients affected with sudden death are basically those with cardiac diseases, like coronary artery disease, dilated or hypertrophic myocardiopathy, arrhythmogenic right ventricular dysplasia and others (1). In these patients the most important way to prevent sudden death is to recognise the disease and treat it accordingly. Some of these patients have, however, a much higher risk of sudden death compared to others. The risk is especially important if they have already presented ventricular arrhythmias, or have a very poor ventricular function. Recognition of this subgroup of very high-risk patients is mandatory in order to treat them aggressively.           

The treatment of choice in these very high-risk patients is the implantation of an automatic defibrillator. This device permanently controls the heart rhythm. If the rhythm is to slow (bradycardia), the device paces the heart at a physiological rate. If the rhythm is too fast (tachycardia) the device restores the normal rate by using either antitachycardia pacing or, if necessary, internal electrical shock as well. Because restoration of the normal rate occurs in the first seconds after initiation of the tachycardia, the haemodynamic consequences are only transient, and the patient survives.

There exists a subgroup of patients in whom sudden death may occur despite the fact that they do not present a demonstrable structural heart disease. Patients in this subgroup suffer from what has been named “electrical diseases”. During the last years, several of these diseases have been identified. These are the long QT syndrome (2), the Brugada syndrome (3), the short QT syndrome (4) and the catecholaminergic polymorphic ventricular tachycardia (5). These are basically familial diseases, based on the presence of genetic defects in some of the electrical channels of the heart. In all of them, the final result is the occurrence of malignant ventricular arrhythmias (polymorphic ventricular tachycardia or ventricular fibrillation) responsible for sudden cardiac death.

Some of these diseases can be recognised by “markers” in the basal electrocardiogram, like a prolonged or shortened QT interval in the long and short QT syndromes respectively (figure 1 a and b), or the presence of right bundle branch block and ST segment elevation in leads V1 to V3 in the Brugada syndrome (figure 1 c). Every physician should be aware of these markers, and recognition of one of them should be enough to initiate a full screening in the patient and his or her family in order to identify the patients at risk for sudden death. As in the previous group, the more effective treatment to prevent sudden death in those patients that are at high risk is the implantation of an automatic defibrillator.

Despite all of these advances in the recognition of different diseases related to sudden death in patients with a structurally normal heart, in some cases still, no disorder can be identified as a cause for the arrhythmia. We consider these patients as suffering from an “idiopathic ventricular fibrillation”. New developments in the future will certainly help to identify new disorders responsible for sudden death in these patients.

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.