Premature Atrial Complex (PAC) and Premature Ventricular Complex (PVC)

Premature Atrial Complex (PAC)

• Also known as a PAC or Atrial Premature Beat

• Occur when part of the atria sends out a depolarisation wave a little too early.

• Cause

  • Potential triggers → smoking, alcohol, coffee
  • Hypokalemia

• Narrow QRS complex with preceding P wave on ECG.

• Generally benign and asymptomatic ectopic (non-sinus) atrial beats.

• No treatment is necessary unless symptomatic.

  • Avoid alcohol and tobacco
  • Beta-blockers may be considered if symptomatic to reduce palpitations.

  <aside> 🧩

  Clues to PACs

  1. The P wave of the PAC looks different from the other P waves, since it starts at a different location in the atria
  2. The P wave and subsequent QRS complex come earlier than would be expected.
  3. The QRS and T wave are followed by a relative pause before the SA node repolarises and initiates a normal beat. </aside>

PAC (Arrow)

Premature Ventricular Complex (PVC)

• Wide QRS complex with no preceding P wave on ECG.
• Ectopic ventricular beats that are generally asymptomatic but can cause palpitations.
• Cause
  • Electrolyte imbalances (e.g., hypokalemia, hypomagnesemia)
  • Digoxin
  • Smoking, alcohol, coffee
• Workup (If Frequent or Symptomatic)
  • 24-hour ambulatory monitoring (Holter monitor)
  • Echocardiography (ECHO)
  • Exercise stress test for patients with unexplained PVCs.
• Beta-blockers can be used if symptomatic to alleviate palpitations.

PVC (Arrow)

Multifocal PVCs (#)

1️⃣ The beat marked by the letter Y in this patient is a premature ventricular contraction (PVC), recognized by a wide QRS complex, opposite-facing T wave, and brief ensuing sinus pause (ie, delayed P wave).
2️⃣ PVCs may result from increased ventricular automaticity leading to spontaneous ventricular depolarization.
3️⃣ Occasional PVCs are normal and considered benign. 4️⃣ When a PVC occurs, it interrupts diastolic filling of the left ventricle, resulting in decreased end diastolic volume (EDV) compared to the previous normal beat (beat X > Y).
5️⃣ The sinus pause that occurs after a PVC allows for longer-than-normal filling time before the next ventricular contraction (ie, prolonged ventricular diastole), which creates increased EDV at the time of the post-PVC beat (beat Z > X).
6️⃣ The greater-than-normal EDV causes a large-stroke volume ventricular ejection, which may be responsible for the palpitations that some patients experience with PVCs