I already know what you’re saying… “PACs aren’t technically a rhythm.” Oh, you weren’t actually saying that? Well, either way, PACs confused me when I was new, so this is for me just as much as it is for you.

Premature atrial complexes occur when an ectopic focus in the atria initiates an impulse before it is time for the next sinus beat1. The waveform on a telemetry strip will be configured differently than a normal P-wave and produce a PR interval that exceeds 120 ms1, 2. The PAC may hide in the preceding T-wave, distorting the T-wave contour1. The video later in this post is a great real-time example, but here’s a static look:

Prior to the fourth QRS, the P-wave is peaked and merged with the previous T-wave

In most cases, PACs occur in healthy individuals without any evidence of heart disease3. Stress, fatigue, and increased consumption of alcohol, caffeine, or nicotine may cause or increase the frequency of PACs1. In the minority of cases, PACs can be a sign of underlying heart condition in the atrium associated with hypertension or coronary artery disease3. Premature atrial complexes may be a warning sign for the development of atrial fibrillation/flutter or of abnormal magnesium or potassium levels2, 3. If a patient is symptomatic, they will likely complain of palpitations3. They may describe a sensation like their heart is missing or skipping a beat. This is because the PAC comes too early in the cardiac cycle to have resulted in an effective heartbeat3.

Generally, PACs do not need to be treated, but since they often signal the development of atrial fibrillation, medications that can alter atrial automaticity and conduction or slow the ventricular response to AF can be considered- beta blockers, calcium channel blockers, and amiodarone2. IV Magnesium sulfate (2g/100mL) may be beneficial in reducing the incidence of PACs in the immediate postoperative period2.

  1. University of Maryland Medical Center Office of Clinical Practice and Professional Development. (2014). Introduction to cardiac rhythm interpretation (6th ed.)
  2. Bojar, R. M. (2016). Manual of perioperative care in adult cardiac surgery (5th ed.). West Sussex, UK: Wiley-Blackwell
  3. Tryzelaar, J. F. (2017). Premature atrial contractions. Retrieved from http://www.cardiachealth.org/premature-atrial-contractions-pacs