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20.14 Cardiac Arrhythmias / Dysrhythmias

Table of Contents

Always exclude underlying structural cardiac disease in all patients with cardiac dysrhythmias 25, 26

20.14.1 Tachyarrythmias:

20.14.1.1 Narrow QRS Complex Tachyarrythmias (SVTs)

Definition Sustained (> 30 seconds) or non–sustained narrow QRS (≤ 0.1 seconds) tachycardias.

Atrial fibrillation

Acute onset (< 48 hours)

  • Assess clinically, e.g. heart failure, mitral stenosis, thyrotoxicosis, hypertension, age and other medical conditions.
  • Consider anticoagulation with heparin or warfarin
  • Synchronized DC cardioversion is occasionally necessary in emergency especially
  • haemodynamic instability or consider if is the first episode.

Non-acute/chronic (> 48 hours)

  • As above, but not immediate DC cardioversion is indicated, unless in hypotensive emergency cases. Anticoagulation with oral warfarin 2mg – 5mg orally once a day for at least a month, then perform elective cardioversion at specialized hospital.

Atrial flutter

  • P waves visible before QRS, commonly occurs, usually 2:1. (150 per minute). P waves, usually negative in Lead II precede QRS, blocked P in ST segment or hidden by QRS.
  • Vagal stimulation with ECG may reveal blocked P waves.

AV Junctional Re-Entry Tachycardias

  • Usually paroxysmal, often young with normal heart.
  • AV nodal re-entry or WPW syndrome. P waves usually not visible (hidden by QRS).

Non-pharmacological Treatment

Electrical Cardioversion.

Synchronized DC cardioversion, 200 J, after sedation with:

A: Diazepam 10–20 mg IV

If flutter has been present longer than 48 hours, defer cardioversion for 4 weeks after anticoagulation with warfarin, unless severe symptoms or heart failure requires urgent cardioversion

Pharmacological Treatment

None is nearly as effective as DC cardioversion.

Consider anticoagulants if Atrial flutter sustained.

Long term treatment: Recurrent atrial flutter is an indication for referral. Many can be cured by radiofrequency catheter ablation.

Atrial tachycardias

  • Rare, often incessant P before QRS (often long PR) or hidden in T
  • May cause heart failure (tachycardia cardiomyopathy).

Atrial fibrillation

Pharmacological Treatment

Initial

  • Anticoagulation with warfarin.
  • Control the ventricular rate with one of the following:
    C: Digoxin oral, 0.25mg daily; use only in heart failure.
    B: Atenolol, oral, 50–100 mg daily (contraindicated in asthmatics).

DC cardioversion in selected cases, after 4 weeks warfarin anticoagulation

Long – term

  • Continue warfarin anticoagulation long-term, unless contraindicated:
    S: Warfarin 5mg daily.
    Monitor INR
  • Maintain therapeutic Range INR 2–3: Stable patients check 3 monthly monitoring If INR < 1.5 or > 3.5: do monthly monitoring

Note: INR monitoring is mandatory for all patients on warfarin.

Rate control:

  • Digoxin only controls rate at rest and is insufficient on its own. If used for longterm, combine with s–blocker.
  • In the elderly and patients with renal impairment:
    C: Digoxin (O) 0.125 mg initial dose
    Adjust dosages according to trough levels within the therapeutic range. Do levels only if the patient has been on the drug for at least 10 days.
    B: Atenolol (O) 50–100 mg daily

20.14.2 AV Junctional Re-Entry Tachycardias

Non-Pharmacological Treatment

Vagal manoeuvres: Valsalva or carotid sinus massage. The patient should be supine and as relaxed as possible, to avoid competing sympathetic reflex

Pharmacological Treatment

If vagal manoeuvres fail:

D: Adenosine, rapid IV bolus, 6 mg through a good IV line, followed by a bolus of 10mL Sodium chloride 0.9% to ensure that it reaches the heart before it is broken down. Run the ECG for 1 minute after the injection. If 6 mg fails, repeat with 12 mg.

If the medicine reaches the central circulation before it is broken down the patient will experience flushing, sometimes chest pain and anxiety. If the tachycardia fails to terminate without these symptoms, the drug did not reach the heart.

If none of the above is effective, or if the patient is hypotensive, consider DC shock

Prevention of recurrent paroxysmal atrial fibrillation

Only in patients with severe symptoms despite the above measures:

  • D: Amiodarone 200 mg (O) 8 hourly for 1 week, followed by 200 mg twice daily for one week and thereafter 200 mg daily. Specialist initiated.

Precautions:

  • Halve dosage of warfarin and monitor INR closely if patient on warfarin, until stable
  • Avoid concomitant digoxin use.

Note: Verapamil and digoxin are contraindicated in WPW syndrome

Long-term treatment: Teach the patient to perform vagal manoeuvres, Valsalva is the most effective. For infrequent, non–incapacitating symptoms:

ß –Blockers

B: Atenolol 50–100 mg (O) daily (If asthmatic)

OR

D: Verapamil (O) 80–120 mg three times daily (Normal heart)

20.14.3 Wide QRS (Ventricular) Tachyarrhythmias (VTs)

Definition: Sustained (> 30 seconds) or non-sustained wide QRS (> 0.12 seconds) tachycardias

Regular Wide QRS Tachycardias

These are ventricular tachycardias until proved otherwise. Regular wide QRS supraventricular tachycardias are uncommon.

Non-pharmacological treatment

Refer all cases after resuscitation and stabilization. Emergency DC cardioversion is mandatory with a full protocol of Cardiopulmonary Resuscitation (CPR)

  • Cardio-pulmonary resuscitation (CPR).
    If no cardiac arrest:
  • DC cardioversion, 200 J, after sedation with: Diazepam, I.V, 10–20 mg If 200 J fails, use 360 J.
    If cardiac arrest: Defibrillate (not synchronized).

Pharmacological Treatment

DC cardioversion is first line therapy for regular wide QRS tachycardias.

Medicines are needed if VT recurs after cardioversion or if spontaneous termination/recurrence.

D: Amiodarone, IV, 5 mg/kg (150mg – 300mg) infused over 30 minutes then continue with maintenance dose to total dose of 1200mg/24 hours

OR

D: Amiodarone 800 mg orally once daily for 7 days, 600 mg/day for 3 days followed by a maintenance dose of 200–400 mg/day

Note: Amiodarone may cause serious long-term side effects due to long half-life.

Therefore, patients require regular monitoring by specialist

B: Lidocaine 50–100 mg (1–2 mg/kg) IV initially and at 5–minute intervals if required to a total of 200–300 mg,

Thereafter, for recurrent ventricular tachycardia only

B: Lidocaine, IV infusion, 1–3 mg/minute for 24–30 hours. Lidocaine will only terminate ± 30% of sustained ventricular tachycardias, and may cause hypotension, heart block or convulsions.

Note:
Never give verapamil IV to patients with a wide QRS tachycardia.
For emergency treatment of ventricular tachycardia, DC cardioversion is first–line therapy, even if stable.

Sustained (> 30 Sec) Irregular Wide QRS Tachycardias

They are usually due to atrial fibrillation with bundle branch block, or pre-excitation (WPW syndrome).

Non-Pharmacological/pharmacological Treatment

  • If the QRS complexes have a pattern of typical right or left bundle branch block, with a rate < less than 170/minute, treat as for atrial fibrillation. See the section on atrial fibrillation.
  • If the rate is > 170 per minute, and/or the complexes are atypical or variable, the likely diagnosis is WPW syndrome with atrial fibrillation, conducting via the bypass tract, DC conversion.

Referral: Refer patient to high care centre for further management

Non–Sustained (< 30 Sec) Irregular Wide QRS Tachycardias

They are usually ventricular. They are common in acute myocardial infarction.

In acute myocardial infarction, only treat non–sustained ventricular tachycardia if it causes significant haemodynamic compromise. Ensure the serum potassium level is above 4 mmol/L

Pharmacological Treatment

Medicines are needed if VT recurs after cardioversion or if spontaneous termination/recurrence.

D: Amiodarone, IV, 5 mg/kg (150mg – 300mg) infused over 30 minutes then continue with maintenance dose to total dose of 1200mg/24 hours

OR

D: Amiodarone 800 mg orally once daily for 7 days, 600 mg/day for 3 days followed by a maintenance dose of 200–400 mg/day

Only in a haemodynamically stable patient:

B: Lidocaine, IV, 50–100 mg (1–2 mg/kg) initially and at 5–minute intervals if required to a total of 200–300 mg

Thereafter, for recurrent ventricular tachycardia only:

B: Lidocaine, IV infusion, 1–3 mg/minute for 24–30 hours

In the absence of acute ischaemia or infarction, consider torsade’s de pointes, due to QT prolonging drugs.

Torsade’s De Pointes Ventricular Tachycardia (VT)

Has a twisting pattern to the QRS complexes and a prolonged QT interval in sinus rhythm

It is usually due to a QT–prolonging drug, ± hypokalaemia.

Non-pharmacological Treatment

  • Cardioversion/defibrillation, as necessary.
  • Torsade’s complicating bradycardia: temporary pacing.

Pharmacological Treatment

Stop all QT-prolonging drugs. Correct serum potassium.

A: Magnesium sulphate 2 g I.V over 5–10 minutes

If recurrent episodes after initial dose of magnesium sulphate:

A: Magnesium sulphate 2 g I.V over 24 hours

Torsade’s complicating bradycardia: temporary pacing.

A: Adrenaline infusion to raise heart rate to > 100 per minute
(if temporary pacing unavailable).

Referral: All cases of wide QRS tachycardia, after resuscitation and stabilization

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