Sudden death definitions and diagnosis

Cardiac Arrest: Diagnosis
Cardiac Arrest is an abrupt cessation of pump function (evidenced by absence of a palpable pulse) of the heart that with prompt intervention could be reversed, but without it will lead to death.

Due to inadequate cerebral perfusion, the patient will be unconscious and will have stopped breathing. The main diagnostic criterion to diagnose a cardiac arrest (as opposed to respiratory arrest, which shares many of the same features) is lack of circulation, however there are a number of ways of determining this.

In many cases, lack of carotid pulse is the gold standard for diagnosing cardiac arrest, but lack of a pulse (particularly in the peripheral pulses) may be a result of other conditions (e.g. shock), or simply an error on the part of the rescuer. Studies have shown that rescuers often make a mistake when checking the carotid pulse in an emergency, whether they are healthcare professionals or lay persons.

Owing to the inaccuracy in this method of diagnosis, some bodies such as the European Resuscitation Council (ERC) have de-emphasised its importance. The Resuscitation Council (UK), in line with the ERC's recommendations and those of the American Heart Association, have suggested that the technique should be used only by healthcare professionals with specific training and expertise, and even then that it should be viewed in conjunction with other indicators such as agonal respiration.

Various other methods for detecting circulation have been proposed. Guidelines following the 2000 International Liaison Committee on Resusciation (ILCOR) recommendations were for rescuers to look for "signs of circulation", but not specifically the pulse. These signs included coughing, gasping, colour, twitching and movement. However, in face of evidence that these guidelines were ineffective, the current recommendation of ILCOR is that cardiac arrest should be diagnosed in all casualties who are unconscious and not breathing normally.

Following initial diagnosis of cardiac arrest, healthcare professionals further categorise the diagnosis based on the ECG/EKG rhythm. There are 4 rhythms which result in a cardiac arrest. Ventricular fibrillation (VF/VFib) and Pulseless Ventricular tachycardia (VT) are both responsive to a defibrillator and so are colloquially referred to as "Shockable" rhythms, whereas Asystole and Pulseless Electrical Activity (PEA) are non-shockable. The nature of the presenting hearth rhythm suggests different causes and treatment, and is used to guide the rescuer as to what treatment may be appropriate (see Advanced Life Support and Advanced Cardiac Life Support, as well as the causes of arrest (below))