Electrical Cardioversion

Electrical cardioversion (synonyms: electrocardioversion; DC cardioversion) is a therapeutic cardiology procedure to restore sinus rhythm (regular heart rhythm) to an existing arrhythmia. Defibrillators are used to establish the correct heart rhythm in a patient with the help of electrocardioversion. A defibrillator is used to apply an electric current to the heart at defined points in the region of the sternum (breastbone) in order to influence the conduction of impulses in the heart. The majority of cardioversions are performed because of atrial fibrillation. In principle, there are two treatment options for patients with atrial fibrillation. On the one hand, there is the possibility of performing rate control with the aim of avoiding tachycardia (persistently accelerated pulse, > 100 beats per minute). On the other hand, however, rhythm control with the goal of restoring sinus rhythm is also available as a therapeutic option. Considering the treatment successes in the presence of both atrial flutter and atrial fibrillation, it can be concluded that restoration of sinus rhythm in patients with atrial fibrillation and flutter by electrical cardioversion offers the greatest chance of success and thus represents the gold standard (procedure of first choice). Note: According to one study, immediate cardioversion is not necessarily required in patients who present to the emergency department of a hospital for symptomatic atrial fibrillation. It was shown that a wait-and-see approach (“Wait and See” strategy) and drug frequency control resulted in an equally good outcome: after 48 hours, 150 of 218 patients (69%) in the “Wait and See” group had sinus rhythm; after 4 weeks, 193 of 212 patients (91%) in the “Wait And See” group versus 202 of 215 patients (94%) in the early cardioversion group had sinus rhythm. The difference between the groups was not significant. Therefore, for the authors, there is no reason to immediately cardiovert all patients with less than 36 hours of AF. However, attention should be directed toward risk assessment of stroke and into initiation of oral anticoagulation (inhibition of blood clotting).

Indications (areas of application)

  • Atrial fibrillation (VHF) and atrial flutter (the terms “fibrillation” and “flutter” describe the frequency of atrial actions); indications for restoration of sinus rhythm in VHF in:
    • Recent onset of VHF
    • Pronounced symptomatology due to atrial fibrillation
    • High heart rate or hemodynamic instability with preexcitation (premature excitation of the ventricle).
    • High heart rate and myocardial ischemia (reduced blood flow to the heart muscle) or hypotension (low blood pressure) or heart failure (cardiac insufficiency), if the heart rate cannot be rapidly reduced pharmacologically
    • Sinus rhythm-maintaining therapy as a longer-term therapeutic goal.
  • Ventricular and supraventricular tachycardia (ventricular: “affecting the ventricle/ventricle of the heart”; supraventricular: “above the ventricles of the heart,” i.e., the cause is in the area of the atria; tachycardia: sustained accelerated pulse, > 100 beats per minute) – the cause of tachycardia can be acquired or congenital. The tachycardia is due to a defect in the conduction of impulses, so that as a result there is an acceleration of the heart rate.

Although electrocardioversion is a low-impact procedure, the majority of patients and physicians question whether the higher risk of complications associated with electrical cardioversion should not be accepted in order to achieve the establishment of stable sinus rhythm through successful cardioversion and thus avoid the major disadvantages and complications of atrial fibrillation. Despite the increased risks during and after the procedure, over a longer period of time electrocardioversion can significantly reduce the risk of thromboembolism, since atrial fibrillation is one of the most important risk factors for the development of thrombus.Furthermore, the use of electrocardioversion can usually massively reduce clinical symptoms, which include dyspnea (subjective breathing difficulties), reduced exercise tolerance, angina pectoris (“chest tightness”; sudden pain in the heart region), and syncope (brief loss of consciousness). The prognostic relevance of atrial fibrillation has been investigated in various clinical trials, for example, in the Framingham study to what extent atrial fibrillation influences all-cause mortality (mortality) independently of concomitant cardiovascular diseases. The presence of atrial fibrillation in some cases doubles mortality, depending on other factors. This finding is of great importance because atrial fibrillation is the most common cardiac arrhythmia in Germany.

Contraindications

  • Pacemaker – if a patient has previously had a pacemaker implanted, this may be a relative contraindication, as electrocardioversion could lead to massive complications. However, the probes can be specially adjusted, so that despite a pacemaker, a safe performance is possible.
  • Thrombi – intracardiac (present within the heart) thrombi are an absolute contraindication, because the risk of detachment of the thrombus with embolism is significantly increased.

Before cardioversion

  • Exclusion of thrombi – before performing electrocardioversion, it is essential to check that no thrombi (blood clots) have formed during the presence of atrial fibrillation, because after electrocardioversion has been performed, the resumption of mechanical activity of the atria may dislodge them and cause emboli (vascular occlusions).
    • In atrial fibrillation (AF) that has been present for less than 48 hours, prior transesophageal echocardiography (TEE; ultrasound examination in which an endoscope (device used for endoscopy) with a built-in transducer is inserted into the esophagus) to rule out thrombi (blood clots) may not be necessary, if necessary.
    • In contrast to acute AF, prior transesophageal echocardiography (TEE) must be performed to exclude thrombi if AF has been present for more than 48 hours. If thrombi are detected, cardioversion should not be performed until they are resolved by effective anticoagulation (blood clotting). Note: If thrombus is detected, repeat TEE should be performed after at least 3 weeks of anticoagulation before cardioversion (IIaC).
  • Thromboprophylaxis:
    • Patients with AF <48 h duration receive only anticoagulation with heparin at the time of cardioversion.
  • Laboratory testing – two laboratory parameters are of great importance in predicting the success of electrocardioversion. Both hypokalemia (potassium deficiency) and hyperthyroidism (hyperthyroidism) should be excluded before the procedure is performed.
  • Anesthesia – Electrocardioversion is performed under short intravenous anesthesia. Etomidate (hypnotic) is usually used for anesthesia, which has the properties of having a rapid but short onset of action and very little effect on cardiac function.

The procedure

Electrocardioversion represents a part of the procedures for cardioversion. However, restoration of regular heart rhythm is not only possible by direct correction of conduction, but can also be done with medication instead. Of critical importance to understanding electrocardioversion is its distinction from acute defibrillation. Although both procedures serve to restore correct cardiac rhythm and are based on the basic principle of using the defibrillator to produce a shock, the two procedures differ significantly in their areas of application. In contrast to acute defibrillation, electrocardioversion starts with a significantly lower energy dose in the start phase. Furthermore, the correction of the heart rhythm in cardioversion is directly dependent on the ECG. Thus, the correction is ECG-triggered so that the shock is delivered by the device during the “R-wave” in the ECG.The “R-wave” describes a precisely defined point in time in the electrocardiogram at which the contraction of the still synchronously working heart muscle cells is registered and subsequently the shock can be applied. The fixed coupling of the shock to the ECG results in a significant reduction in the risk of ventricular fibrillation. In this regard, biphasic current delivery (biphasic cardioversion) is clearly superior to monophasic current delivery and has success rates of more than 90%.Electrical cardioversion is performed under continuous ECG monitoring and intravenous short-acting anesthesia.Because of the possibility of ventricular fibrillation or asystole occurring, resuscitation measures must be planned. Advantages of electrocardioversion over pharmacologic (drug) cardioversion.

  • Both short-term and long-term success rates of electrocardioversion are significantly higher than those of drug cardioversion.
  • Furthermore, there is an immediate improvement in cardiac rhythm after cardioversion has been performed. The short-term success can be verified by parallel ECG monitoring.
  • In electrical cardioversion with biphasic defibrillator of recent onset atrial fibrillation, conversion rates to sinus rhythm can be expected in 90% of cases. In contrast, with pharmacological cardioconversions only in 70% of cases.

Disadvantages of electrocardioversion compared with pharmacological (drug) cardioversion.

  • To perform electrocardioversion, it is necessary that the procedure be performed under short intravenous anesthesia. No anesthesia is required for the drug treatment option.
  • Shock generation with the help of the defibrillator has the possibility of triggering further pathological arrhythmias and thus further worsening the symptomatology.
  • As already noted, the performance of electrocardioversion can trigger embolism due to the detachment of a thrombus from the atrium of the heart.

After cardioversion

  • After electrical cardioversion in a patient with present atrial fibrillation, detectable impairment of left atrial function is present for at least another week after the procedure is performed. This functional impairment, which is present despite restored sinus rhythm, is also referred to as atrial “stunting.” Based on this, even after electrical cardioversion, it should be noted that intracardiac thrombi may continue to form in the short term, so that there is still a potential risk of a subsequent cardioembolic event.
  • Thromboprophylaxis:
    • In the presence of atrial fibrillation that has been present for less than 48 hours and a CHA2DS2-VASc score (score used to estimate the risk of apoplexy) of 0, four weeks of anticoagulation (anticoagulant) can be omitted because thrombus formation usually cannot occur within two days. If risk factors for thromboembolism are present, anticoagulation for at least 4 weeks after cardioversion is required.Patients with atrial fibrillation < 48 h duration receive only anticoagulation with heparin at the time of cardioversion.
    • In contrast to acute atrial fibrillation, VHF lasting longer than 48 h must be observed that the patient is treated with anticoagulants (anticoagulants; phenprocoumon/Marcumar; possibly also heparin or NOAK) for at least four weeks.

Possible complications

  • The most common complication is recurrence of the previously present arrhythmia. However, there is an option to repeat cardioversion or to add drug cardioversion.
  • In addition to the occurrence of skin irritation and allergic reactions to drugs can further embolisms (embolism incidence / frequency of new cases of disease: 1.3%) – usually within 7 days after cardioversion – occur, which in the worst case can be lethal (fatal).
  • Other possible complications include thromboembolism (stroke) and significant bleeding. These are stated in the literature with about 0.5-1% each.

Further notes

  • Successful cardioversion improves cerebral blood flow (CBF).Stable sinus rhythm (regular heart rhythm) by cardioversion caused CBF to increase from 507 to 627 ml/min. Likewise, brain perfusion increased significantly from 35.6 ml/100 g/min to 40.8 ml/100 g/min. This is potentially important in view of cognitive deficits in long-standing AF. Further studies need to clarify to what extent this has positive consequences for the cognitive function of successfully cardioverted patients.