Heart Education
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What a Premature Junctional Contraction (PJC) Looks Like on Your Watch ECG

QALY Team
Premature Junctional Contraction (PJC) on smartwatch ECG (Apple Watch, Kardia, Samsung, Fitbit)

Key Takeaways

The heart has a specialized structure called the atrioventricular node or AV node. The AV node electrically connects the heart's upper chambers, or atria, with the heart’s bottom chambers, or ventricles in order to coordinate beating at the top of the heart. The AV node is part of your heart's electrical system.

On some occasions, electrical impulses start in this AV node, or “ junction” between the atria and ventricles. This impulse fires prematurely, disrupting your heart’s normal rhythm. Most people who experience PJCs report the feeling of their heart “skipping a beat.” While PJCs are more common as we age, here are some possible causes:

  • Medications, e.g., Digitalis toxicity: Digitalis (digoxin or digitoxin) is a medicine that treats heart failure and arrhythmias. Digitalis toxicity can happen if you take too much of this medicine or your body can’t process it properly. Digitalis toxicity is the most common cause of PJC.
  • Consuming caffeine
  • Coronary artery disease
  • Drinking alcohol.
  • Electrolyte Imbalance
  • Hypoxemia
  • Heart failure
  • Smoking or using tobacco products

How to Spot PJCs on Your Watch ECG

PJCs are usually identified during a routine electrocardiogram or ECG test. Other tests that can rule out PJCs are the Holter monitoring and stress tests. All of these tests will have to be done at a healthcare facility. If you are using a smartwatch with an ECG monitoring feature, you can use your smartwatch’s ECG monitoring capability to identify PJCs at home.

To identify a PJC, look for the following characteristics in your ECG:

  • Premature P wave, usually inverted or without a preceding P wave or with a retrograde P wave, may appear before, during, or after the QRS complex.
  • Narrow/normal QRS complex, identical to the other normal beats.
  • PR interval may be shorter than normal or absent
  • PJC is followed by a long pause as the heart works to restore its normal rhythm.

A PJC also interferes with the normal rhythm by coming in early before the next anticipated beat. Since PJCs are very common, there are times when there may only be one episode of a PJC in 24 hours. In cases where a PJC happens more frequently than that, they can be identified and categorized according to their pattern.

  • Bigeminy – a PJC on every second beat
  • Trigeminy – a PJC on every third beat
  • Quadrigeminy – a PJC on every fourth beat
  • Couplet – two consecutive PJCs

Example of Premature Junctional Contraction (PJC) caught with Apple Watch

Example of Premature Junctional Contraction (PJC) caught with Apple Watch

Common Symptoms and Treatment Options for PJC

Most PJC findings are incidental because most people don’t exhibit any symptoms. However, symptoms can include:

  • A flutter in your chest
  • Heart pounding
  • Chest pain
  • Shortness of breath
  • Dizziness

Your healthcare provider will manage your PJCs depending on the underlying cause. Some of the most common treatments for PJCs are the following:

  • Regular exercise
  • Restricting alcohol and caffeine intake
  • Discontinuing tobacco use
  • Correcting electrolyte levels
  • Avoiding stress
  • Adjusting your digitalis dose if you currently take this medication.
  • Medication to treat digitalis toxicity
  • Surgical procedures such as cardiac ablation

Any Cause for Concern?

PJCs are less common than other types of extra heartbeats, such as premature atrial contractions (PACs) or premature ventricular contractions (PVCs). Occasional PJCs are generally not a cause of concern for healthy individuals and should go away without any treatment. A PJC is deemed frequent if there are more than 100 episodes of PJCs in 24 hours.

Frequent and regular PJCs can lead to junctional tachycardia, a fast heartbeat that comes from the heart’s junction. Junctional tachycardia may require treatment, such as medication, to slow the heart to a steady pace.

As always, if you show signs of a potential PJC, contact your healthcare provider as soon as possible to rule out the presence of harmful underlying conditions.

Still Not Sure How to Spot Premature Junctional Contractions on Your Watch ECG?

Your smartwatch can be your partner in looking after your heart. If you’re concerned about premature junctional contractions, get your smartwatch ECGs analyzed by experts within minutes on the QALY app: iOS and Android.

Get second opinions of your ECGs by human experts on the QALY app!

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