Lecture on Premature Ventricular Contractions (PVCs)

Introduction to PVCs

• PVCs (Premature Ventricular Contractions): A type of ectopic beat originating from irritable ventricular foci.
• Similar to PACs (Premature Atrial Contractions): Both involve irritable ectopic foci but differ in origin.

Irritation of Ventricular Focus

• Causes of Irritation: Hypoxia

  • Low oxygen in the blood
  • Causes: anemia, lung issues (COPD, asthma, pneumonia, pneumothorax), decreased cardiac output (CHF, cardiogenic shock, obstructive shock)

• Electrolyte Abnormalities

  • Cations like potassium, calcium
  • Fluctuations can cause agitation

• Increased Sympathetic Nervous System Activity

  • Fight or flight response
  • Increased epinephrine and norepinephrine

• Stimulants

  • Cocaine
  • ADHD medications (methylphenidate, methamphetamines)

• Infarcted or Scar Tissue

  • Scar tissue may lead to reentrant circuits
  • Reentrant circuits can cause high heart rates

Recognizing PVCs on an EKG

• Counting Rate

  • Count R waves in a 6s rhythm strip
  • Multiply by 10 to get beats per minute (bpm)

• Rhythm Analysis

  • Measure R to R interval
  • Irregular intervals indicate irregular rhythm

• P Waves

  • Identifying P waves before QRS complexes
  • AV dissociation if there's no P wave before each QRS (especially in PVCs)

• QRS Complexes

  • PVCs have wide QRS complexes
  • Abnormal path because they don't follow the normal conduction system (SA node, AV node, bundle of His, bundle branches, Purkinje fibers)
  • Wide QRS due to abnormal conduction from ectopic focus or reentrant circuit

Patterns in PVCs

• Ventricular Bigeminy & Trigeminy
  • Bigeminy: PVC after every normal P-QRS complex
  • Trigeminy: PVC after every two normal P-QRS complexes

Ventricular Tachycardia (V-tach)

• Definition: More than three PVCs in a row
• Characteristics:
  • Wide and regular QRS complexes
  • Tachycardic rate (greater than 100 bpm)
• Potential Danger: V-tach can be pathological

Reviewing Case EKGs

• Example EKG Analysis: Identifying irregular intervals, P waves, QRS width, and recognizing V-tach patterns
• Recognizing Regular and Irregular Patterns: Using lead direction to identify ectopic foci

Conclusion

• Next Steps: Future lectures will cover topics such as Torsades de Pointes, V-tach, and V-fib.
• Resources: Encouragement to follow and support via social media and Patreon