Unit 4: Rhythm Recognition and Arrhythmias

• Topic 01

  Normal Sinus Rhythm — Diagnostic Criteria

  15 questions
• Topic 02

  Sinus Tachycardia and Sinus Bradycardia

  15 questions
• Topic 03

  Sinus Arrhythmia and Sinus Pause/Arrest

  15 questions
• Topic 04

  Supraventricular Arrhythmias — PAC, SVT, Atrial Flutter, Atrial Fibrillation

  15 questions
• Topic 05

  Ventricular Arrhythmias — PVC (Unifocal, Multifocal, Couplets), V-Tach, V-Fib

  15 questions
• Topic 06

  Junctional Rhythms — Junctional Escape, Accelerated Junctional

  15 questions
• Topic 07

  Heart Blocks — First, Second (Type I and II), and Third Degree (Complete)

  15 questions
• Topic 08

  Pacemaker Rhythms — Paced Beats, Capture, and Sensing Failures

  15 questions
• Topic 09

  Life-Threatening Rhythms — V-Fib, Asystole, PEA, and Emergency Response

  15 questions

A few questions from this unit, with the answer and a full explanation. The complete bank is available when you start practising.

1. A patient on digoxin therapy develops PVC bigeminy with PVCs in a pattern of couplets. The patient has a potassium level of 3.0 mEq/L. Which combination of factors is contributing to the ventricular ectopy, and what is the management priority?

   • A
     Digoxin toxicity combined with hypokalaemia (which potentiates digoxin toxicity); correct hypokalaemia, check serum digoxin level, and hold further digoxin
     Correct answer
   • B
     Lidocaine infusion should be started immediately to suppress the PVCs before any other action
   • C
     The PVCs are benign and require no intervention regardless of the drug history or potassium level
   • D
     Hypokalaemia alone is the cause; digoxin protects against ventricular ectopy
   Explanation

   Digoxin toxicity causes ventricular arrhythmias by inhibiting the Na+/K+ ATPase pump, increasing intracellular calcium and enhancing ventricular automaticity. Hypokalaemia potentiates digoxin toxicity because low extracellular potassium increases digoxin binding to the Na+/K+ ATPase pump, amplifying its toxic effects. The management priority is to check serum digoxin level, correct hypokalaemia with IV potassium replacement, and withhold further digoxin. Key takeaway: hypokalaemia potentiates digoxin toxicity — always check and correct potassium in digoxin-related ventricular arrhythmias.

2. What is an agonal rhythm and how does it appear on ECG?

   • A
     A narrow-complex rhythm at 40–60 bpm representing junctional escape
   • B
     A preterminal rhythm with slow (less than 20 bpm), wide, irregular complexes from dying myocardium that quickly deteriorates to asystole
     Correct answer
   • C
     A regular sawtooth baseline at 300 bpm consistent with atrial flutter
   • D
     A chaotic irregular baseline with no discernible waveforms, identical to VF
   Explanation

   Agonal rhythm is a preterminal electrical pattern from severely ischaemic or dying myocardium, characterised by very slow (<20 bpm), wide, irregular QRS complexes. It produces no effective cardiac output and rapidly degenerates into asystole. It is not shockable and requires CPR plus epinephrine. Recognising agonal rhythm is important to distinguish it from other ventricular rhythms. Key takeaway: agonal rhythm = very slow (<20 bpm) wide irregular complexes, preterminal, non-shockable.

3. A 65-year-old patient with severe heart failure has a rate of 80 bpm, upright P waves in I and II, PR 0.18 s, narrow QRS, and regular rhythm. Her physician says 'the ECG shows NSR'. What is the correct interpretation of this finding?

   • A
     NSR cannot be present in heart failure — the diagnosis must be incorrect
   • B
     NSR requires a QRS >0.12 s in patients with heart failure
   • C
     Heart failure always produces atrial fibrillation, so the interpretation is wrong
   • D
     NSR is present; NSR is an electrical finding only and does not exclude structural heart disease or heart failure
     Correct answer
   Explanation

   NSR is a purely electrical diagnosis describing how impulses are generated and conducted. Structural heart disease — including severe heart failure, valvular disease, and cardiomyopathy — can coexist with NSR. The ECG characterises rhythm and conduction, not myocardial contractility or structural anatomy. This is a common misconception among students. Key takeaway: NSR is an electrical finding only — structural heart disease can always coexist with NSR.