Cardioversion is a medical procedure that uses a controlled electrical shock to restore a normal heartbeat in individuals experiencing abnormal heart rhythms (arrhythmias). The aim is to momentarily reset the heart’s electrical system, allowing its natural pacemaker to re-establish a regular rhythm.
Understanding Electrical Energy in Cardioversion
Electrical energy is fundamental to cardioversion, with “joules” serving as the standard unit of measurement. A cardioversion device, often called a defibrillator, charges a capacitor to a specific energy level in joules before delivery. This controlled electrical current briefly halts the heart’s abnormal electrical activity, allowing its own electrical system to restart in a normal, synchronized pattern.
Factors Influencing Energy Levels
The amount of electrical energy, measured in joules, used during cardioversion is not fixed and varies based on several considerations. One primary factor is the specific type of arrhythmia being treated. For instance, atrial fibrillation (AFib) typically requires initial biphasic energy levels ranging from 120 to 200 joules, while monophasic devices might start at 200 joules and escalate to 360 joules if needed. Atrial flutter and supraventricular tachycardia (SVT) generally respond to lower energy, often between 50 and 100 joules for biphasic shocks, or 100 joules for monophasic. Ventricular tachycardia with a pulse usually requires 100 joules with biphasic and 200 joules with monophasic devices.
Patient characteristics also influence the energy setting. A patient’s body size and chest impedance, which is the resistance to electrical current flow through the chest, can affect how much energy is needed. Larger patients or those with higher impedance may require more joules to ensure effective current delivery to the heart.
The duration of the arrhythmia is another consideration; recent-onset atrial arrhythmias often respond to lower energy, whereas longer-standing conditions might necessitate higher joule settings. If initial lower energy shocks are unsuccessful, medical professionals may increase the joule setting in subsequent attempts. Underlying heart conditions and certain antiarrhythmic medications can also influence the heart’s responsiveness to the electrical shock.
Monophasic Versus Biphasic Cardioversion
The type of electrical waveform delivered by the cardioversion device significantly impacts the energy levels required for a successful procedure. Monophasic devices represent an older technology where the electrical current flows in a single direction through the heart. These devices generally necessitate higher energy settings to achieve the desired therapeutic effect. For example, monophasic cardioversion for atrial fibrillation often begins at 200 joules, with subsequent shocks potentially increasing to 360 joules.
In contrast, biphasic devices are more modern and widely used. They deliver an electrical current that flows in one direction and then reverses. This two-phase approach makes biphasic waveforms more efficient, allowing for successful cardioversion with lower energy levels than monophasic devices.
For atrial fibrillation, biphasic shocks typically range from 120 to 200 joules, though some protocols may start as low as 75 joules. For atrial flutter, biphasic energies can be as low as 20 to 30 joules, and up to 100 joules. This efficiency translates to less energy delivered to the patient, which may reduce potential side effects such as skin burns or myocardial damage.
The Cardioversion Procedure Overview
Preparation for an electrical cardioversion procedure begins with specific patient instructions. Individuals are typically asked to fast for at least six to eight hours before the procedure and to avoid applying lotions or oils to their chest. Patients may also be instructed to take certain blood-thinning medications for several weeks prior to the procedure, or undergo a transesophageal echocardiogram (TEE) to check for blood clots in the heart, mitigating the risk of stroke. All jewelry must be removed before the procedure.
During the procedure, an intravenous (IV) line is inserted, and the patient receives medication for sedation or a short-acting anesthetic to ensure comfort and no memory of the shock. Large adhesive pads, serving as electrodes, are placed on the chest to deliver the electrical energy. The healthcare team continuously monitors the heart’s electrical activity, blood pressure, and oxygen levels. The controlled electrical shock is delivered through these pads, aiming to reset the heart’s rhythm. Following the shock, the patient is observed until sedation wears off and can typically return home the same day, with instructions to avoid driving or operating machinery for 24 hours.