| Ventricular fibrillation. Ventricular fibrillation (VF) begins as a quasiperiodic reentrant pattern of excitation in the ventricles with resulting poorly synchronized and inadequate myocardial contractions. The heart consequently immediately loses its ability to function as a pump. As the initial reentrant pattern of excitation breaks up into multiple smaller wavelets, the level of disorganization increases. Sudden loss of cardiac output with subsequent tissue hypoperfusion creates global tissue ischemia; brain and myocardium are most susceptible. VF is the primary cause of sudden cardiac death (SCD).
History
- VF often occurs without forewarning. The following symptoms, while not necessarily specific for SCD or VF, may develop before any major cardiac event:
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- Chest pain and other angina equivalents
- Dyspnea
- Easy fatigue
- Palpitations
- Syncope
- Immediately preceding acute cardiac arrest, possible increase in heart rate, presence of premature ventricular contractions (PVCs), or period of VT
Physical
- No pulse or respiration
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- Unconsciousness
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- Wide and chaotic QRS complexes on cardiac monitor
Prehospital Care
Because of the critical importance of early defibrillation, prehospital care is vital for arrests due to VF that occur outside the hospital. Interventions that impact survival and outcome of resuscitation include the following:
- Witnessed or early recognition of an arrest
- Early activation of emergency medical services (EMS) system
- Bystander CPR slows the degeneration of VF and improves survival.
- Automated external defibrillator (AED) application and defibrillation by trained personnel in the field
- AEDs have revolutionized prehospital VF management because they decrease the time to defibrillation. This is accomplished by having the units prepositioned in the field where cardiac arrests are likely to occur (eg, airports, casinos, jails, malls, stadiums, industrial parks), eliminating the need for rhythm-recognition training and increasing the number of trained personnel and laypeople that can defibrillate at the scene.
- AEDs are programmed to recognize 3 shockable rhythms: coarse ventricular fibrillation, fine ventricular fibrillation, and rapid ventricular tachycardia. Modern units have a sensitivity greater than 95% and specificity approaching 100% for the 3 shockable rhythms. The greatest difficulty is in distinguishing fine ventricular fibrillation from asystole.
- AEDs can also be used for children. A pediatric dose-attenuating system should be used, if available, for children up to the age of 8 years, and a conventional AED can be used for children at or older than 8 years or with a corresponding weight of at least 25 kg (55 lb).
- Early access to trained EMS personnel capable of performing CPR, defibrillation, and advanced cardiac life support (ACLS)
Date: 2015-01-12; view: 755
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