User:Peter Gheeraert/Primary ventricular fibrillation

Primary ventricular fibrillation is an unpredictable and potentially fatal arrhythmia occurring during the acute phase of a myocardial infarction leading to immediate collapse and, if left untreated, leads to sudden cardiac death within the first minutes. In the developed countries primary ventricular fibrillation is a leading cause of death. World wide the annual number of deaths caused by primary ventricular fibrillation might be comparable to the number of death caused by road traffic accidents. A substantial proportion of these deaths can be avoided by seeking immediate medial attendance during symptoms of acute myocardial infarction. If treated promptly, most patients have a life expectancy comparable to that of other patients without this complication during myocardial infarction.

Definition
It is traditionally defined as ventricular fibrillation during a clinically uncomplicated acute myocardial infarction. More specifically the term primary refers to the absence of clinical heart failure or shock preceding the onset of ventricular fibrillation. Consequently, the term secondary ventricular fibrillation refers to ventricular fibrillation complicating  heart failure or shock during the acute phase of myocardial infarction.

Incidence
Approximately 10 % of all myocardial infarctions are complicated by primary ventricular fibrillation. The incidence peaks between 20 and 50 minutes after the  onset of the acute myocardial infarction. With the current delays in seeking medical attendance for acute myocardial infarction two thirds (2/3) of the primary ventricular fibrillations occur before medical attendance and of these medically unattended events 2/3 occur after more than 30 minutes of warning symptoms of acute myocardial infarction. 

Risk factors
The risk for ventricular fibrillation during acute myocardial infarction not complicated by heart failure or shock is related to the magnitude of ST elevation, the presence of (mild) hypopotassemia, the absence of pre-infarction angina, the size of the infarction and the presence of an occlusion in the left coronary artery. Other risk factors, with moderate evidence include: younger age, male gender, first degree relatives with sudden death and probably some specific forms of warning ventricular arrhythmias.

Mechanisms
The multiplicity of ischemia related factors is rather overwhelming    including depletion of adenosine triphosphate, acidosis, extracellular accumulation of potassium ion, intracellular accumulation of calcium and sodium ions, cell-to-cell uncoupling, generation of free radicals, increased level of plasma free fatty acid concentrations, release of catecholamines, reduced excitability, abbreviation of action potential duration, and altered mechanical properties of the ischemic tissue. In humans it is currently not possible to target any of these experimental parameters in order to manage or prevent ventricular fibrillation during myocardial ischemia or infarction.

Survival
The survival of PVF largely depends on the immediate presence or absence of an external defibrillator and the promptness of the defibrillation. The success rate of prompt defibrillation during monitoring is currently higher than 95%. The success rate of defibrillation decreases dramatically for each minute of delay to defibrillation, estimated -10% per minute.

Prognosis
After return of spontaneous circulation the hospital course is further characterized by a moderately higher risk of death compared to patients without PVF (relative risk from 1.0 to 2.8.) Whether this still hold true with most recent treatment strategies (earlier hospital admission and immediate angioplasty with thrombus aspiration) is unknown. PVF does not affect the long-term prognosis. Among those who survived the hospital admission the reported one year mortality rates of patients with PVF (3%, 4.1% and 8% are not higher than the mortality rates of those without PVF in the respectively reference groups. More recently, for 339 consecutive patients with PVF during AMI treated by defibrillation followed by primary angioplasty the survival rate after 30 days with a mean follow up of 3.7 years was 94% comparable to controls (with comparable age, gender and infarction size) of which 92 % survived.