Cardiac Rhythm Quiz

Methods for Calculation

• Method 1: Counting Large Boxes

  • Regular heart rhythms are determined by counting large boxes between R waves.
  • The number is divided into 300 to calculate beats per minute (bpm).
  • A reference chart provides easy calculation for 1–6 large boxes.
  • The ratio is based on 60 seconds/minute divided by 0.20 seconds/large box equals 300 large boxes/minute.

• Method 2: Counting Small Boxes

  • The most accurate method involves counting small boxes between R waves.
  • The result is divided by 1500 to get bpm.
  • The reference is 60 seconds/minute divided by 0.04 seconds/small box equals 1500 small boxes/minute.
  • Examples are available for calculating bpm given a specific number of small boxes.

• Method 3: Six-Second ECG Rhythm Strip

  • For irregular rhythms, count R waves in a 6-second strip and multiply by 10.
  • This gives the approximate beats per minute (bpm).

Methods 1 and 2 for Calculating Heart Rate

• A table provides calculated heart rates for various numbers of large and small boxes.

Sinus Rhythm

• Normal Sinus Rhythm (NSR):

  • Average rate: 60-100 bpm.
  • Rhythm: Regular.
  • P waves: Upright and uniform.
  • PR interval: 0.12-0.20 sec.
  • QRS: 0.06-0.10 sec.

• Sinus Bradycardia:

  • Rate: Below 60 bpm.
  • Rhythm: Regular.
  • P waves: Upright and uniform.
  • PR interval: 0.12-0.20 sec.
  • QRS: 0.06-0.10 sec.

• Sinus Rhythm with Sinoatrial (SA) Block:

  • The block occurs in multiple of PP intervals.
  • After dropped beat, the cycle continues in time.
  • Atrial and Ventricular rates vary based on duration and frequency of the SA block.
  • P waves are normal (upright and uniform).

• Sinus Pause (Sinus Arrest):

  • The SA node momentarily fails to discharge.
  • The pause (arrest) time interval is not a multiple of the PP interval (normal).
  • Atrial and Ventricular rates vary based on duration and frequency of this pause.
  • P waves are normal (upright and uniform).

• Sinus Tachycardia:

  • Rate: Above 100 bpm.
  • Rhythm: Regular.
  • P waves: Upright and uniform.
  • PR interval: 0.12-0.20 sec.
  • QRS: 0.06-0.10 sec.

• Sinus Arrhythmia:

  • Usually normal rate (60-100 bpm).
  • Rhythm: Irregular (varies with respiration).
  • The difference between the shortest and longest RR intervals is greater than 0.12 seconds.
  • P waves: Upright and uniform.
  • PR interval: 0.12-0.20 sec.
  • QRS: 0.06-0.10 sec.

Atrial Rhythm

• Wandering Atrial Pacemaker (WAP):

  • Pacemaker site transfers between the SA node, atria, and AV junction.

• Atrial Tachycardia:

  • Rapid atrial rate overrides the SA node.
  • P waves: At least three different forms (determined by atrial focus).
  • PR interval: Variable (determined by focus).

• Multifocal Atrial Tachycardia (MAT):

  • Ventricular rate is often above 100 bpm.
  • Can resemble atrial fibrillation but has visible P waves.
  • Rate: 150-250 bpm.
  • PR interval may be short in rapid rates.

• Supraventricular Tachycardia (SVT):

  • Fast heart rate.
  • P waves may not be seen (buried in T waves).
  • Rate: Above 100 bpm.

• Premature Atrial Contraction (PAC):

  • Early contraction before the expected sinus beat.
  • Sinus rhythm usually returns afterward.
  • P waves may be buried in preceding T waves and difficult to see.

• Paroxysmal Atrial Tachycardia (PAT):

  • Abrupt onset and offset of rapid heart rate.

• Atrial Flutter (A-flutter):

  • AV node conducts at 2:1, 3:1, 4:1 (or greater) ratio.
  • Flutter waves have a saw-toothed appearance.

• Wolff-Parkinson-White (WPW) Syndrome:

  • Accessory pathway between atria and ventricles.
  • Rapid impulse transmission.
  • QRS slurred initial portion (delta wave).

• Atrial Fibrillation (A-fib):

  • Erratic atrial electrical discharge from multiple foci.
  • No organized atrial depolarization.
  • Irregular R-R intervals.

Junctional Rhythm

• Junctional Rhythm:

  • Pacemaker located in the AV junction.
  • Rate: 40-60 bpm.
  • Rhythm: Regular.
  • P waves: Absent, inverted, buried, or retrograde.

• Accelerated Junctional Rhythm:

  • Rate: 61-100 bpm.
  • Rhythm: Regular.

• Junctional Tachycardia:

  • Rate: 101-180 bpm.
  • Rhythm: Regular.

• Junctional Escape Beat:

  • Escape complex after the expected sinus complex.

• Premature Junctional Contraction (PJC):

  • Enhanced automaticity in the AV junction.

Ventricular Rhythm

• Idioventricular Rhythm:

  • Rate: 20-40 bpm.
  • Rhythm: Regular.
  • P waves: Absent. Wide QRS complexes.

• Accelerated Idioventricular Rhythm:

  • Rate: 41-100 bpm.
  • Rhythm: Regular.
  • P waves: Absent. Wide QRS complexes.

• Premature Ventricular Contraction (PVC):

  • Contraction from an irritable ventricular focus.
  • Can be uniform or multiform.
  • Compensatory pause (sinus node timing not interrupted).
  • Noncompensatory pause (PVC resets sinus node timing).

• PVC Various Patterns:

  • PVC occurs every 2nd beat (bigeminy).
  • PVC occurs every 3rd beat (trigeminy).
  • PVC occurs every 4th beat (quadrigeminy).
  • Paired PVCs (couplets).
  • Interpolated PVC.
  • PVCs on the T wave (R-on-T).

• Ventricular Tachycardia (VT):

  • Monomorphic VT - QRS complexes have identical shape and amplitude.
  • Polymorphic VT - QRS complexes vary in shape and amplitude. Long QT intervals common.

• Torsade de Pointes:

  • Irregular polymorphic VT with a characteristic "twisting of points" on the ECG.

• Ventricular Fibrillation (VF):

  • Chaotic electrical activity; no ventricular contraction.

Atrioventricular (AV) Block

• First-Degree AV Block:

  • Prolonged PR interval (greater than 0.20 seconds).

• Second-Degree AV Block, Type I (Mobitz I or Wenckebach):

  • Progressive lengthening of PR intervals until a P wave is not followed by a QRS complex.

• Second-Degree AV Block, Type II (Mobitz II):

  • Conduction ratio is commonly 2:1, 3:1, or 4:1 (or variable).

• Third-Degree AV Block:

  • Complete block between atria and ventricles.
  • Atrial and ventricular activity is independent but usually regular.

Pacemaker Rhythm

• Single-Chamber Pacemaker Rhythm (Atrial and Ventricular):

  • Pacemaker spike is evident. Atrial and ventricular pacemaker spike differs in pattern.

• Dual-Chamber Pacemaker Rhythm (Atrial and Ventricular):

  • Both atrial and ventricular pacing are discernible.

• Pacemaker Failure to Sense:

  • Pacemaker fails to detect native heartbeats.

• Pacemaker Oversensing:

  • Pacemaker inappropriately recognizes native heartbeats as inappropriate.

• Loose Electrodes:

  • Loose connections at the electrode tip.

• Baseline Varies with Respiration:

  • ECG trace affected by breathing.

Unknown/Dead

• Pulseless Electrical Activity (PEA):

  • Identifiable rhythm, no pulse.
  • Possible sinus, atrial, junctional, or ventricular rhythms.

• Asystole:

  • Complete absence of ventricular electrical activity.

Test your knowledge on the different types of cardiac rhythms and their characteristics. This quiz covers irregular heartbeats, the organization of rhythms, and the implications of various electrical failures in the heart. Perfect for medical students and healthcare professionals looking to refresh their understanding.