a stimulation output circuit to deliver neural stimulation pulses;

a plurality of electrodes configured to sense a plurality of subcutaneous electrocardiogram (ECG) vectors indicative of cardiac cycles each including a predetermined type timing reference event, the plurality of electrodes configured for placement external to the circulatory system;

a reference event detection circuit coupled to the plurality of electrodes, the reference event detection circuit adapted to detect the predetermined type timing reference event using the plurality of subcutaneous ECG vectors;

a cardiac parameter measurement circuit coupled to the plurality of electrodes and adapted to measure an atrioventricular interval;

a stimulation control circuit coupled to the stimulation output circuit and the reference event detection circuit and adapted to adjust delivery of neural stimulation pulses using the measured atrioventricular interval, the stimulation control circuit including:

an offset interval generator adapted to produce an offset interval starting with the predetermined type timing reference event; and

a pulse delivery controller adapted to start a delivery of a burst of the neural stimulation pulses when the offset interval expires; and

an implantable housing configured to contain at least the stimulation output circuit, the reference event detection circuit, the cardiac parameter measurement circuit, and the stimulation control circuit, the implantable housing including a hermetically sealed can being an electrode of the plurality of electrodes.