ECG signal

Dr Diana R Holdright

Consultant Cardiologist

Dr Diana Holdright

Treatments - Cardioversion

Patients who are troubled with symptoms arising from an abnormal heart rhythm, such as atrial fibrillation may be eligible for a procedure called a cardioversion to restore normal heart rhythm. This involves delivering one or more electrical shocks to the chest using metal paddles whilst the patient is under a general anaesthetic. Cardioversion is most successful in patients with a structurally normal heart, demonstrated on an echocardiogram and in whom the abnormal heart rhythm is a new finding.

When the heartbeat becomes irregular, the atria, the collecting chambers at the top of the heart, no longer contract in a mechanically useful way, causing a degree of stasis to blood flow and predisposing to clot formation within the chambers, and in particular within a finger-like projection called the left atrial appendage. The shock that is delivered to the chest may cause pre-existing clots in the heart to break free and enter the circulation, which could lead to a heart attack or stroke, and as such a patient is required to take warfarin or a similar drug for a few weeks before and after the procedure. Warfarin thins the blood and reduces the likelihood of clot formation; only when the INR, the marker of how thin the blood is, has been consistently around the 2.5 mark (i.e. when the patient’s blood is approximately 2.5 times thinner than normal) will the cardioversion be carried out. Patients will also generally be required to have a TOE (Transoesophageal Echocardiogram) immediately prior to the delivery of the shock, to be sure that there are no residual clots despite anticoagulation. Some arrhythmias, however, such as ventricular fibrillation are life-threatening, and require immediate treatment, and this is called defibrillation; for this reason defibrillators can now be found alongside first aid kits in many airports, train stations, football stadia and department stores.

Elective cardioversions generally only take about 10 minutes, which includes giving the general anaesthetic immediately beforehand. The patient will be admitted to hospital as a day case and will need to be nil by mouth for four to six hours beforehand because of the general anaesthetic and the period of recovery after this. During the cardioversion itself, the patient will be connected to an ECG machine to monitor the heart rhythm, and the doctor will place two pads on the chest. A brief, controlled shock, usually 200 J, is delivered to the chest via two metal paddles, and the doctor will be able to see immediately if this has restored normal sinus rhythm via the ECG monitor; it is not uncommon, however, for the rhythm to return to normal briefly, and then flip back into the arrhythmia. If the first shock is ineffective, a further shock will be delivered, and if this still fails to restore sinus rhythm, a third and slightly larger shock, usually 360 J, will also be delivered. At this point, if sinus rhythm has not been restored, the doctor may decide to accept the arrhythmia as the patient’s normal rhythm moving forward.

Following the procedure the chest may feel a little sore from the delivery of the shocks, but otherwise it is generally well tolerated. The patient will require observation for a few hours while the effects of the anaesthetic wear off, but will typically be discharged on the same day and should make arrangements to be driven home afterwards.

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