Amzon Web Services (AWS) - Aggregating DynamoDB Data

We have a DynamoDB Database that is storing machine sensor information in the "structure" of :

HashKey: MachineNumber (Number) SortKey: EntryDate (String) Columns: SensorType (String), SensorValue (Number)

The sensors generate information almost every 3 seconds and we're looking to measure a (near) real-time KPI to count how many machines in a region were down in the past hour for more than 10 minutes. A region can have close to 10000 machines so iterating through DynamoDB is taking almost 10+ minutes for a response. What is the best way to do this?