Electrocardioversion

In 1962, Bernhard Lown et al. described electrocardioversion for the first time (Zürn 2012).

Electrocardioversion (ECV) is the attempt to convert a pathological heart rhythm, such as atrial fibrillation (AF), atrial flutter, ventricular tachycardia, etc., into sinus rhythm by applying current (Reitgruber 2021).

Cardioversion is the gold standard for patients with atrial fibrillation and atrial flutter. It is also used as an emergency cardioversion for ventricular flutter (Er 2007).

Electrocardioversion is differentiated between the following devices:

- external electrocardioversion with mono- and biphasic devices

- implanted cardioverter defibrillator (AICD)

- automated external defibrillators (AED).

The latter devices are used for early defibrillation by laypersons. These devices are now widely available and have been shown to increase survival rates when ventricular fibrillation occurs outside the hospital (Herold 2022).

- Procedure:

Before cardioversion, atrial thrombi must be excluded by transesophageal echocardiography (TEE) (Er 2007).

The patient must have been fasting for at least 6 h and laboratory values (see below) must be available. A well placed i.v. access is obligatory. If the patient is a pacemaker patient, the pacemaker should be set to "bipolar sensing" (Er 2007).

If the patient is conscious, short-acting anesthesia with e.g. propofol 50 - 100 mg or etomidate 2 mg / ml, of which 4 - 8 ml should be administered rapidly i. v. (Weihrauch 2020) should be induced first (Herold 2022) and the patient should then be laid flat on his back. Throughout cardioversion, all vital signs such as ECG, peripheral oxygen saturation, and blood pressure should be monitored. The procedure is performed with personnel, medications, and machine resuscitation ready (Er 2007).

During defibrillation, rescuers must have no contact with the patient or bedside (Herold 2022).

Monophasic devices:

The choice of energy here depends on the rhythm disturbance

- 360 J at the 1st impulse and also at further impulses if the following clinical picture is present:

- ventricular flutter

- ventricular fibrillation

- polymorphic ventricular tachycardia (Herold 2022)

- 200 J in case of:

- atrial fibrillation

- atrial flutter

- monomorphic ventricular tachycardia (Herold 2022)

Biphasic devices:

Here, 150 - 360 J, depending on the type of device should be set at the 1st surge (200 J in case of uncertainty). If unsuccessful, further surges of increasing energy are required (Herold 2022).

Tachycardias:

In tachycardias, current delivery is synchronized, also referred to as cardiac phase-controlled, so that current delivery does not fall into the vulnerable phase of T (i.e., not into the ascending T-leg). Therefore, current delivery occurs 0.02 seconds after the R- jag (Herold 2022).

Ventricular fibrillation:

In ventricular fibrillation, current delivery is not R-wave triggered (Herold 2022).

Atrial fibrillation:

In this case, electrocardioversion is possible on an outpatient basis, provided that there is no structural heart disease and the patient is monitored on a monitor for at least 3 h after the procedure. The procedure of electrocardioversion for VHF depends on the duration of atrial fibrillation (Zürn 2012):

If AF exists < than 48 h, electrocardioversion should be performed immediately and under heparin protection (Zürn 2012).

If atrial fibrillation has been present for longer than 48 h, the risk of thrombus formation in the atria is very high. These patients should be anticoagulated (INR 2 - 3 [Er 2007]) for at least 4 weeks before cardioversion. As an alternative to anticoagulation, safe exclusion of thrombus by TEE can also be performed.

If thrombus is already present, anticoagulation is required for at least 3 weeks. This should be followed by another TEE check (Zürn 2012).

Electrodes should be positioned antero-posteriorly in VCF, as this is associated with higher success of cardioversion.

If the patient has an implanted pacemaker or defibrillator, a biphasic shock shape should also be selected. In this case, the electrodes should also be positioned antero-posteriorly, but at a distance from the aggregate of at least 8 cm (Zürn 2012).

There may be a loss of stimulus response due to cardioversion (so-called loss of capture). In very rare cases, the pacemaker may be irreversibly damaged (Spes 2022).

After successful cardioversion, the patient should be anticoagulated for 4 weeks (Herold 2022). Depending on certain risk factors (see CHA2 DS2 - VASc - Score [Stierle 2017]), lifelong anticoagulation may also be required (Zürn 2012).

Pharmacodynamics

A massive direct current shock is delivered over the chest. This simultaneously depolarizes all cardiac cells capable of generating or transmitting impulses and then synchronously transfers them to their refractory phase. This so-called "electrical quiescence" in the myocardium is followed by an initial spontaneous depolarization in the sinus node region in those cells that exhibit the lowest resting membrane stability. Potentially, however, it is also possible that the rhythm event continues to be dominated by arrhythmia-induced ectopic foci, so-called autonomic automatic centers (Herold 2022).

Indication

• Absolute indication:
  • Hemodynamically unstable patients with atrial fibrillation (Zürn 2012).
  • supraventricular tachycardia with impending cardiogenic shock
  • ventricular tachycardia with impending cardiogenic shock
  • Ventricular fibrillation
  • ventricular flutter (Herold 2022)
  • Relative Indication:
  • Atrial fibrillation
  • Failure of drug therapy for atrial flutter (Herold 2022).

According to ESC 2016, there is a recommendation or evidence level I / B for electrical cardioversion for acutely hemodynamically unstable patients. Indications for electrical cardioversion can be:

- unsuccessful cardioversion with medication

- hemodynamic instability (Sauerbruch 2018).

There is little correlation between arrhythmia and symptoms in VHF. Up to 60% of patients are asymptomatic and 40% of patients have VHF symptoms despite sinus rhythm.

Symptoms may include:

- Dyspnea

- palpitations

- dizziness

- Decrease in exercise tolerance

- angina pectoris

- occurrence of embolism (sometimes first symptom)

- Rare occurrence of syncope (Pinger 2019)

- Polyuria (ANP effect; atrial natriuretic peptide causes, among other things, increased excretion of sodium and chloride by the kidney)

(Herold 2022)

In atrial fibrillation, the so-called EHRA- classification (classification of the European Heart Rhythm Association) can be used to assign the severity of symptoms.

Modified EHRA Classification:

• Class I: There are no symptoms at all, so-called "silent AF".
• Class II: Symptoms occur. Depending on the severity of the symptoms, one differentiates between:
  • Class II a: There are only mild symptoms, the daily activity is not restricted, also called "not troublesome".
  • Class II b: There are moderate symptoms, which do not affect daily activities, so-called "patient troubled by symptoms
• Class III: Severe symptoms occur. Normal daily activities are significantly impaired.
• Class IV: At this stage, normal activities of daily living are no longer possible. One speaks of so-called "disabling symptoms" (Pinger 2019 / Kirchof 2016).

The success of cardioversion depends largely on two laboratory abnormalities:

- hypokalemia

- hyperthyroidism

Therefore, in the optimal case, a normokalemia and a euthyroid metabolic state should be present (Er 2007).

The following complications can occur with ECV:

- thromboembolic events

- occurrence of arrhythmias

- complications of anesthesia (Zürn 2012)

Contraindication

Cardioversion is contraindicated under digitalis intoxication existing non-life threatening tachycardia (Herold 2022).

The AFFIRM and RACE studies showed that rate control is not inferior to rhythm control. Preserving sinus rhythm in VHF (rhythm control) does not improve mortality. Only an improvement in symptoms can be achieved (Zürn 2012).

Electrocardioversion may particularly benefit (younger) patients with frequent and severe symptoms (Mickley 2004).

The success of electrocardioversion in VHF can be improved by prior administration of antiarrhythmic drugs and reduce the risk of recurrence (Zürn 2012).

In persistent AF, ambulatory biphasic electrocardioversion has been shown to be more favorable than monophasic shock delivery. On average, lower energy levels (203 joules versus 570 joules) and fewer shock deliveries (1.5 versus 2.9) were required than with monophasic shock delivery (Neumann 2004). Also, myocardial damage and the risk of skin burns are lower in this case (Zürn 2012).

The success rate in studies was 100% for biphasic electrocardioversion and 73.7% for monophasic (Neumann 2004).

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