Cardiac Rhythm Quiz

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).

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

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.

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:
- 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.

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.

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.

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.

Pulseless Electrical Activity (PEA):
- Identifiable rhythm, no pulse.
- Possible sinus, atrial, junctional, or ventricular rhythms.
Asystole:
- Complete absence of ventricular electrical activity.