The purpose of this study is to characterize performance of the MARVEL algorithm downloaded into the MicraTM TPS to provide atrial synchronous ventricular pacing in subjects with AV block.

A sub-study will be conducted within the Marvel study, the purpose of this study is to characterize the MARVEL algorithm in patients who were enrolled in the MARVEL study, and to collect and compare the accelerometer signals and AV synchrony at a second point in time.

Inclusion Criteria:

• Subject has been implanted with, or is expected to be implanted with a MicraTM TPS (Model MC1VR01), with remaining device longevity of 6 years or more.
• Subject is ≥ 18 years old and as per required local law.
• Subject has atrioventricular (AV) block.
• Subject (and/or witness, as applicable per local regulations) provides signed and dated authorization and/or consent per institution and local requirements.
• Subject is willing and able to comply with the protocol.

Exclusion Criteria:

• Subject is in atrial arrhythmia at the time of enrollment.
• Subject is currently enrolled or planning to participate in a potentially confounding drug or device trial during the study. Co-enrollment in concurrent trials is only allowed when documented pre-approval is obtained from the Medtronic study manager.
• Subject is pregnant (if required by local law, women of child-bearing potential must undergo a pregnancy test within seven days prior to MARVEL study procedures).
• Subject meets any exclusion criteria required by local law (age or other).

Additional criteria for the MARVEL Evolve Sub-study:

Inclusion criteria:

• Subjects in the MARVEL Sub-Study have previously been enrolled in the MARVEL main study