Defibrillation is a medical procedure that delivers a controlled electrical shock to the heart. This intervention aims to reset the heart’s electrical activity when it experiences certain life-threatening rhythm disturbances.
Understanding Defibrillation
Defibrillation works by delivering an electrical current to the heart, which briefly depolarizes a large portion of the heart muscle. This sudden electrical discharge aims to stop chaotic electrical activity, allowing the heart’s natural pacemaker to regain control and re-establish a normal rhythm. It is specifically used for abnormal heart rhythms such as ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT), where the heart quivers ineffectively instead of pumping blood. A defibrillator cannot restart a heart that has completely stopped, a condition known as asystole or “flatline.”
When and How Defibrillation is Applied
Defibrillation is performed during cardiac arrest when a shockable rhythm like ventricular fibrillation or pulseless ventricular tachycardia is identified. The standard protocol involves immediate initiation of cardiopulmonary resuscitation (CPR). After approximately two minutes of CPR, the heart rhythm is assessed using a defibrillator.
If a shockable rhythm is detected, a defibrillation shock is delivered. Following the shock, CPR is immediately resumed for another two minutes before the rhythm is re-evaluated. This cycle of CPR, rhythm assessment, and shock (if indicated) continues. This highlights that defibrillation is not limited to a fixed number of attempts, but rather involves continuous assessment and intervention based on the patient’s condition and heart rhythm.
Factors Influencing Multiple Defibrillation Attempts
Several factors influence the decision to continue or cease defibrillation attempts. The duration of cardiac arrest before the first shock significantly impacts success rates; prolonged delays decrease the likelihood of successful defibrillation. The effectiveness of ongoing CPR, including consistent chest compressions at a rate of 100-120 per minute and a depth of 2 to 2.4 inches (5 to 6 cm), is also a strong determinant of success. High-quality CPR minimizes interruptions, which is important for maintaining blood flow to the heart and brain.
Underlying medical conditions, such as acidosis (an excess of acid in the body fluids) and hypoxia (low oxygen levels), can hinder the effectiveness of defibrillation. Medical professionals also look for and address reversible causes of cardiac arrest, often remembered by “H’s and T’s” such as hypovolemia (low blood volume), hypothermia, toxins, or thrombosis (blood clots). The patient’s response to previous shocks, or lack thereof, also guides real-time decisions, meaning the process is dynamic and not limited by a set number of shocks.
What Happens When Defibrillation is Unsuccessful
When repeated defibrillation attempts do not restore a stable heart rhythm, medical professionals employ other interventions. Medications such as epinephrine are often administered intravenously every three to five minutes to help support blood pressure and heart function. Antiarrhythmic drugs like amiodarone or lidocaine may also be given to help suppress abnormal rhythms.
Addressing underlying reversible causes remains a focus, as correcting issues like severe electrolyte imbalances or drug overdoses can improve the chances of successful resuscitation. Continuous high-quality CPR is maintained throughout these interventions to provide blood flow to the vital organs. If all measures have been exhausted and there is no return of spontaneous circulation, medical teams make a difficult decision regarding the cessation of resuscitation efforts, based on established protocols and the patient’s overall prognosis.