Micra Atrial Tracking Using a Ventricular Accelerometer Study

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