Chapter 08. Rhythm Recognition

Rhythm recognition is a critical skill in Advanced Life Support (ALS) as it determines the appropriate management strategy for a patient in cardiac arrest. Accurate interpretation of the rhythm allows clinicians to decide whether to deliver a shock (defibrillation) or focus on CPR and drug therapy.

 Importance of Rhythm Recognition in ALS

✔ Determines whether defibrillation is needed.
✔ Helps guide drug therapy (adrenaline, amiodarone).
✔ Identifies underlying cardiac causes of arrest.
✔ Differentiates shockable vs non-shockable rhythms.
✔ Informs post-resuscitation care and prognosis.

The ALS cardiac arrest algorithm is based on classifying the cardiac rhythm into two major categories:

1. Shockable rhythms (Defibrillation required)

• Ventricular Fibrillation (VF)
• Pulseless Ventricular Tachycardia (pVT)

2. Non-Shockable rhythms (No defibrillation – focus on CPR & drug therapy)

• Asystole
• Pulseless Electrical Activity (PEA)

 Shockable Rhythms (VF & pVT)

🔹 Require immediate defibrillation + CPR

1. Ventricular Fibrillation (VF)

✔ Most common initial rhythm in sudden cardiac arrest (SCA).
✔ Caused by chaotic, disorganised electrical activity in the ventricles.
✔ No effective cardiac output → leads to rapid death if untreated.

🔹 ECG Features of VF:

• No P waves, QRS complexes, or T waves.
• Irregular, chaotic waveform with no organised activity.
• Varying amplitude and frequency of fibrillation waves.

🔹 Causes of VF:

• Acute myocardial infarction (MI) / ischaemia.
• Electrolyte imbalances (hyperkalaemia, hypokalaemia, hypocalcaemia).
• Severe hypoxia or acidosis.
• Brugada syndrome, long QT syndrome (genetic arrhythmias).

🔹 ALS Management of VF:

1. Immediate defibrillation (150–200J biphasic or 360J monophasic).
2. Resume CPR immediately after shock (do not check pulse).
3. Reassess rhythm every 2 minutes during CPR.
4. Give adrenaline 1 mg IV after the 2nd shock.
5. Give amiodarone 300 mg IV after the 3rd shock.

2. Pulseless Ventricular Tachycardia (pVT)

✔ Rapid, wide QRS complex tachycardia without a pulse.
✔ Caused by a ventricular ectopic pacemaker firing at high speed.
✔ If untreated, degenerates into VF and cardiac arrest.

🔹 ECG Features of pVT:

• Wide QRS complexes (>120ms) at a rapid rate (>100 bpm).
• No associated P waves.
• May be monomorphic (regular) or polymorphic (irregular, varying QRS).

🔹 Causes of pVT:

• Acute MI, ischaemia.
• Electrolyte imbalances (hyperkalaemia, hypokalaemia, hypomagnesaemia).
• Cardiomyopathy or structural heart disease.
• Drug toxicity (tricyclic antidepressants, antiarrhythmics, digoxin toxicity).

🔹 ALS Management of pVT:

• Same as VF:
  1. Immediate defibrillation.
  2. CPR for 2 minutes.
  3. Adrenaline (1 mg IV after 2nd shock).
  4. Amiodarone (300 mg IV after 3rd shock).

 Non-Shockable Rhythms (Asystole & PEA)

🔹 Managed with CPR & Adrenaline – No Defibrillation

3. Asystole ("Flatline")

✔ Complete absence of electrical activity in the heart.
✔ Worst prognosis of all cardiac arrest rhythms.
✔ Can be primary (due to MI) or secondary (due to prolonged hypoxia, metabolic disturbances).

🔹 ECG Features of Asystole:

• Flat or nearly flat line (confirm in two leads).
• No P waves, QRS complexes, or T waves.
• Occasional agonal P waves may be seen.

🔹 ALS Management of Asystole:

1. High-quality CPR immediately.
2. Give adrenaline (1 mg IV every 3–5 min).
3. Identify and treat reversible causes (4 Hs & 4 Ts).
4. Reassess rhythm every 2 minutes – if VF/pVT develops, defibrillate.

 Do not attempt defibrillation – it will not help asystole.

4. Pulseless Electrical Activity (PEA)

✔ Electrical activity is present on ECG, but there is no effective cardiac output.
✔ Commonly caused by reversible conditions (4 Hs & 4 Ts).

🔹 ECG Features of PEA:

• Normal or abnormal QRS complexes without a pulse.
• May look like sinus rhythm, bradycardia, or even VT without a pulse.

🔹 Causes of PEA (4 Hs & 4 Ts):

• Hypoxia, Hypovolaemia, Hyper/Hypokalaemia, Hypothermia.
• Thrombosis (MI/PE), Tamponade, Tension pneumothorax, Toxins.

🔹 ALS Management of PEA:

1. High-quality CPR immediately.
2. Give adrenaline (1 mg IV every 3–5 min).
3. Identify and correct reversible causes (4 Hs & 4 Ts).
4. Reassess rhythm every 2 minutes.

 Do not attempt defibrillation – it is not effective for PEA.

 Summary of Rhythm Recognition in ALS

 Key ALS Takeaways for Rhythm Recognition

✔ Shockable rhythms (VF/pVT) require immediate defibrillation.
✔ Non-shockable rhythms (Asystole/PEA) require CPR and adrenaline – No defibrillation.
✔ Identify and treat reversible causes (4 Hs & 4 Ts) to improve survival.
✔ Regular rhythm checks should be performed every 2 minutes during CPR.
✔ Always confirm asystole in two ECG leads to rule out fine VF.