for people ages 18 years and up (full criteria)
Healthy Volunteers
healthy people welcome
at San Francisco, California
study started
completion around
Principal Investigator
by Greg Marcus, MD, MAS
Headshot of Greg Marcus
Greg Marcus



Premature atrial contractions (PACs) and premature ventricular contractions (PVCs) are observed in the majority of individuals monitored for more than a few hours. Although the clinical course of PACs and PVCs is usually benign, it has been described that high PAC or PVC frequency causes various comorbidities and worsens outcomes in different patient groups. For example, PACs can initiate episodes of atrial fibrillation, and PAC count is highly specific in predicting diagnosis of incident atrial fibrillation. Increasing PVC frequencies are an important predictor of incident heart failure.

While conventional wisdom dictates that common environmental exposures determine PAC and PVC frequencies, this has not born out in rigorous studies. Whether PAC and PVC frequencies may have genetic underpinnings remains unknown.

Comparisons between identical twins and fraternal twins can provide estimates of heritability. Fraternal twins are an ideal control because, like identical twins, they share a womb, have the same birthday, and their environment while growing up are as similar as between identical twins. However, while identical twins share approximately 100% of the same inherited DNA, fraternal twins share, on average, about 50%. By monitoring identical and fraternal twins with portable electrocardiograms (ECGs), we will be able to count the PACs and PVCs over a consecutive timespan to describe the familial aggregation of these complexes. This, to our knowledge, would be the first study to compare PAC and PVC frequencies in identical and same-sex fraternal twins, providing the first assessment of how genetical inheritance may influence cardiac ectopy burdens.

Official Title

The Heart Rhythm Twins Study -- A Pilot Study in Identical and Fraternal Twins


Premature Atrial Complex, Premature Ventricular Contraction, twin, Premature Birth, Ventricular Premature Complexes, Atrial Premature Complexes, Identical twins, Same-sex fraternal twins


You can join if…

Open to people ages 18 years and up

  • Identical or same-sex fraternal sets of twins
  • English-speaking

You CAN'T join if...


  • UCSF accepting new patients
    San Francisco California 94143 United States

Lead Scientist at UCSF

  • Greg Marcus, MD, MAS
    Dr. Gregory Marcus is a specialist in the treatment of arrhythmias, including mapping and catheter ablation for atrial fibrillation, supraventricular tachycardias and ventricular arrhythmias. He is also an expert in pacemaker, biventricular device and defibrillator implantation. RESEARCH Dr. Marcus is Associate Chief of Cardiology for Research at UCSF Health. He is also an Ass…


accepting new patients
Start Date
Completion Date
University of California, San Francisco
Study Type
Expecting 120 study participants
Last Updated