Frequency domain monitoring of myocardial electrical stability

An implantable system for monitoring myocardial electrical stability, comprising:

• one or more pulse generator configured to pace a patient's heart for a period of time using a patterned pacing sequence that repeats every N beats, where N is an integer that is at least 3;
• one or more sensing circuit configured to obtain an electrical signal that is representative of a plurality of consecutive beats of the patient's heart while the patient's heart is being paced using the patterned pacing sequence that repeats every N beats;
• a controller configured to
• divide the plurality of consecutive beats into a plurality of sets of N consecutive beats;
• select 2 of the N beats, for each set of N consecutive beats, to produce a sub-set of 2 beats per set of N consecutive beats;
• transform time domain data, associated with the plurality of sub-sets of 2 beats, to frequency domain data;
• determine, based on the frequency domain data, an alternans magnitude at 0.5 cycles/beat;
• and
• monitor myocardial electrical stability based on the alternans magnitude at 0.5 cycles/beat.