An implantable medical device, comprising: a multi-dimensional accelerometer configured to sense motion corresponding to a plurality of vectors; and a processor configured to: evaluate the plurality of vectors by: receiving a signal from the accelerometer for each of the plurality of vectors; determining a first value of a metric from the signal for each of the plurality of vectors during a first sensing condition; determining a second value of the metric from the signal for each of the plurality of vectors during a second sensing condition; determining a difference between the first and second values of the metric determined for the first sensing condition and the second sensing condition for each of the plurality of vectors, characterised in that: the processor is further configured to select, based upon the determined differences, one of the plurality of vectors for monitoring the patient; and in that: the implantable medical device further comprises: a therapy delivery module controlled by the processor to adjust a therapy delivery control parameter in response to values of the metric determined from the accelerometer signal for the selected vector during patient monitoring. a multi-dimensional accelerometer configured to sense motion corresponding to a plurality of vectors; and a processor configured to: evaluate the plurality of vectors by: receiving a signal from the accelerometer for each of the plurality of vectors; determining a first value of a metric from the signal for each of the plurality of vectors during a first sensing condition; determining a second value of the metric from the signal for each of the plurality of vectors during a second sensing condition; determining a difference between the first and second values of the metric determined for the first sensing condition and the second sensing condition for each of the plurality of vectors, evaluate the plurality of vectors by: receiving a signal from the accelerometer for each of the plurality of vectors; determining a first value of a metric from the signal for each of the plurality of vectors during a first sensing condition; determining a second value of the metric from the signal for each of the plurality of vectors during a second sensing condition; determining a difference between the first and second values of the metric determined for the first sensing condition and the second sensing condition for each of the plurality of vectors, receiving a signal from the accelerometer for each of the plurality of vectors; determining a first value of a metric from the signal for each of the plurality of vectors during a first sensing condition; determining a second value of the metric from the signal for each of the plurality of vectors during a second sensing condition; determining a difference between the first and second values of the metric determined for the first sensing condition and the second sensing condition for each of the plurality of vectors, characterised in that: the processor is further configured to select, based upon the determined differences, one of the plurality of vectors for monitoring the patient; and in that: the implantable medical device further comprises: a therapy delivery module controlled by the processor to adjust a therapy delivery control parameter in response to values of the metric determined from the accelerometer signal for the selected vector during patient monitoring.