Electrical cardioversion is a medical procedure used to restore a normal heart rhythm when a person experiences an abnormal heartbeat, known as an arrhythmia. This treatment delivers a controlled electric shock to the heart, aiming to reset its natural electrical activity. Its purpose involves addressing rhythms that are too fast or irregular, which can lead to health issues.
What is Electrical Cardioversion?
Electrical cardioversion involves delivering a controlled electric shock to the heart. This shock aims to briefly stop the heart’s abnormal electrical activity, allowing its natural pacemaker to reset. Electrode pads are placed on the chest, and sometimes the back, which connect to the cardioversion machine.
A key distinction in this procedure is between synchronized and unsynchronized cardioversion. Synchronized cardioversion delivers a lower-energy shock precisely timed with the R-wave on an electrocardiogram (ECG). This timing avoids triggering a more dangerous arrhythmia. Unsynchronized cardioversion, often referred to as defibrillation, delivers a higher-energy shock immediately without timing. This method is reserved for life-threatening emergencies with no coordinated electrical activity, such as ventricular fibrillation or pulseless ventricular tachycardia.
The Science Behind Joule Settings
Joule settings quantify the energy delivered during the electric shock. This energy resets the heart’s cells simultaneously, interrupting abnormal electrical circuits. The goal is to provide enough energy to restore a normal rhythm without causing unnecessary damage to the heart muscle or surrounding tissues.
Several factors influence appropriate joule settings. Patient body size affects transthoracic impedance (resistance to electrical current); higher impedance may require higher energy levels. The specific arrhythmia also dictates energy requirements. The type of defibrillator, monophasic or biphasic, significantly impacts settings. Biphasic devices, delivering current in two directions, are more effective at lower energy levels than older monophasic devices, potentially reducing the risk of skin burns and myocardial damage.
Typical Joule Settings for Different Conditions
Joule settings vary depending on the specific type of arrhythmia and defibrillator technology. Medical professionals tailor these settings to individual patient circumstances, considering factors like arrhythmia duration and overall health. Biphasic defibrillators generally require less energy than monophasic devices for the same result.
For atrial fibrillation (AFib), initial biphasic shock settings typically range from 100 to 200 joules. If AFib has been present for two days or less, 100 J may be recommended; longer durations might start at 150 J. Monophasic defibrillators often use 200 joules or greater, potentially escalating to 360 joules if needed.
Atrial flutter typically requires lower energy levels for successful cardioversion. Biphasic devices often start at 50 joules. For monophasic devices, an initial shock of 50 J can be effective, though some studies suggest 100 J may lead to higher first-shock success rates.
For ventricular tachycardia (VT) with a pulse, an initial energy setting of 50 to 100 joules is commonly used for stable monomorphic VT, regardless of whether a monophasic or biphasic device is employed. If the initial shock is unsuccessful, energy levels may be gradually increased in subsequent attempts. However, if the ventricular tachycardia is polymorphic (irregular) or if the patient is unstable and pulseless, higher, unsynchronized shocks (defibrillation doses) are typically required. Supraventricular tachycardia (SVT), a broad category of fast heart rhythms originating above the ventricles, often responds to initial biphasic energy settings of 50 to 100 joules.
Patient Experience and Safety Considerations
Before an electrical cardioversion, patients typically receive medication to induce sedation or a brief, short-acting general anesthesia. This ensures comfort during the procedure, as the electric shock, though brief, can be uncomfortable. During the procedure, medical staff continuously monitor the patient’s heart rate, blood pressure, breathing, and oxygen levels. The electric shock itself lasts for only a fraction of a second, and while multiple shocks may be necessary, the patient remains asleep throughout.
After cardioversion, patients recover under observation. Most can return home the same day but should arrange for a driver due to sedation. While generally safe, potential risks include skin redness or burns, and a rare but significant risk is blood clot dislodgment, which could lead to stroke or pulmonary embolism. To mitigate this, patients often receive blood-thinning medications for several weeks before and after the procedure. Rarely, the procedure may cause other heart rhythms or temporary heart damage.