Chapter 08. Rhythm Recognition MCQ Questions

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:

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

High-quality CPR immediately.
Give adrenaline (1 mg IV every 3–5 min).
Identify and treat reversible causes (4 Hs & 4 Ts).
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:

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

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

Summary of Rhythm Recognition in ALS

Rhythm	Defibrillation?	ECG Features	Primary Treatment
Ventricular Fibrillation (VF)	Yes	Chaotic, disorganised waves, no P, QRS, T	Defibrillation + CPR + Adrenaline + Amiodarone
Pulseless VT (pVT)	Yes	Wide QRS, tachycardia, no pulse	Defibrillation + CPR + Adrenaline + Amiodarone
Asystole	No	Flatline or near-flat, no QRS	CPR + Adrenaline + Treat reversible causes
PEA	No	Any organised rhythm with no pulse	CPR + Adrenaline + Treat reversible causes

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.

Chapter 08. Rhythm Recognition

Importance of Rhythm Recognition in ALS

Shockable Rhythms (VF & pVT)

1. Ventricular Fibrillation (VF)

2. Pulseless Ventricular Tachycardia (pVT)

Non-Shockable Rhythms (Asystole & PEA)

3. Asystole ("Flatline")

4. Pulseless Electrical Activity (PEA)

Summary of Rhythm Recognition in ALS

Key ALS Takeaways for Rhythm Recognition

Subtopics

Chapter 8.

08.01 Techniques for ECG monitoring

08.02 Diagnosis from cardiac monitors

08.03 Basic electrocardiography

08.04 How to read a rhythm strip

08.05 Cardiac arrest rhythms

08.06 Peri-arrest arrhythmias

08.07 The QT interval