Basic principles

Tachycardia is defined as a heart rate above 100/min.

Severe tachycardia leads to decreased cardiac output due to:

• Shortening of the diastole and insufficient ventricular filling
• Myocardial ischemia (perfusion of coronary arteries is possible only in diastole, which is shorter in tachycardia, so the coronary blood flow is decreased)

Cardiac output usually decreases with a heart rate > 150/min, but it depends on age and physiological reserves.
Estimated maximum heart rate: 220 – age

The tolerance of tachycardia worsens with increasing heart rate.
Sinus tachycardia is not a dysrhythmia; it is a consequence of other physiologic or pathologic conditions and is usually better tolerated.

Management of tachycardia

• ABCDE approach
  Give oxygen if SpO2 <94 %, obtain IV access, Monitor ECG, blood pressure, SpO2
  Record 12-lead ECG if possible (it should not delay the treatment)
  Identify and treat reversible causes (e.g. hypoxia, pain, anxiety, ischemia, acidemia, electrolyte abnormalities, hypovolaemia)

Tachycardia in haemodynamically unstable patient

Electrical cardioversion

• Delivery of a controlled and synchronized DC shock to the heart to restore sinus rhythm (up to 3 attempts)

• Start with biphasic shock with energy of 120-150 J in broad complex tachycardia and atrial fibrillation, increase the energy if unsuccessful. For atrial flutter and regular narrow complex tachycardia, lower energy is sufficient. Choose biphasic shock 70 – 120 J.

• The myocardium is electrically vulnerable during cardiac repolarization (T wave on ECG)

• Delivering a DC shock during repolarization may induce ventricular fibrillation, which is why DC shock has to be synchronized with QRS (highest point of R wave)

• Once ECG is attached and synchronized mode is enabled, look for synchronizing markers on ECG and verify that R waves are correctly recognized
  Adjust the position of ECG leads if R waves are not recognized correctly

• In awake patients, sedation or anaesthesia is required before delivering the shock
  

  After 3 unsuccessful attempts to restore the rhythm,

  administration of amiodarone 300 mg IV over 10 - 20 minutes (risk of hypotension with shorter duration) is indicated, followed by another synchronized shock (if the patient is still haemodynamically unstable)
  

Amiodarone

• The most widely used antiarrhythmic drug in intensive care with the potential to treat both atrial and ventricular dysrhythmias

• Prolongs QT interval (do not use in polymorphic ventricular tachycardia with long QT - torsade de pointes)

• Slows down conduction through the AV node (do not use in patients with history of atrial fibrillation with preexcitation for risk of inducing ventricular fibrillation)

• Dilute in 5% dextrose.

• Give 300 mg IV over 20 minutes for haemodynamically unstable tachycardia, followed by 900 mg infusion over 24 hours.

• During CPR, in a shockable rhythm, give 300 mg IV bolus after 3rd shock and 150 mg after 5th shock.
  

Management of haemodynamically stable tachycardia

• This is described in the poster, which is part of the 2021 ERC guidelines

• Depends on the regularity of the rhythm (regular or irregular) and the width of the QRS - broad (>0,12 s) or narrow QRS (<0,12 s)

• Narrow QRS suggests supraventricular origin of tachycardia

Although the algorithm is a required knowledge, some treatment options might not be known to non-specialists and consulting a cardiologist is recommended whenever possible.