The purpose of this study is to compare short term (up to 48 hours) traditional cardiac rhythm monitoring using a standard ambulatory Holter monitor versus long term (up to 14 days), continuous ambulatory cardiac rhythm monitoring using a new device cleared by the FDA (Zio® Patch), iRhythm Technologies, Inc., San Francisco CA) in patients with suspected cardiac arrhythmias.

This is a prospective, observational study of patients seen in the Holter lab at Scripps Green Hospital and other Scripps Clinic locations. Only patients who have indications for traditional cardiac rhythm monitoring will be enrolled in the study. Patients 18 years or older with suspected arrhythmias capable of providing informed consent will wear both a traditional Holter monitor for up to 48 hours and a Zio® Patch for up to 14 days. Both devices will be initiated at the same time as they do not interfere with one another. This will also allow a direct comparison of the same initial up to 24 hour monitoring period between the two devices. As the Zio® Patch is worn for up to 14 days instead of only 24 hours, it will be assessed if in the physician's opinion (referring physician), waiting for the extended time hinders being able to provide medical care and/or diagnosis for the patient.

Inclusion Criteria:

• Are being seen in the outpatient office for evaluation, treatment, or follow-up of arrhythmias;
• Have a medical history for which ascertaining whether asymptomatic arrhythmias is occurring could be helpful in their treatment plan;
• Are capable of giving informed consent; assessed by the investigator or the Study Coordinator;
• Are 18 years of age or older;
• Able to comply with long term continuous monitoring ECG device.

Exclusion Criteria:

• Have known skin allergies, conditions, or sensitivities (e.g. allergy to adhesives, psoriasis) as the Zio(R)Patch should not be used on patients with known skin allergies, conditions, or sensitivities; or
• Are receiving pacing therapy (e.g., from a pacemaker); or
• Are anticipated to receive or require external cardiac defibrillation during the monitoring period; or
• Are anticipated to be exposed to high frequency surgical equipment during the monitoring period.

Patients 18 years of age of greater with suspected arrhythmias.