Abstract: Method and apparatus for detecting changes in electrocardiogram signals. A first cardiac electrogram signal is sensed, where the first cardiac electrogram signal has a voltage and includes a first cardiac complex. A ventricular activation is detected in the first cardiac complex and a first timer is started, where the first timer times a first specified time. A first voltage value is measured from the first cardiac electrogram signal at the first specified time after the ventricular activation. A second voltage value is also measured from a defined portion of the first cardiac electrogram signal. A comparison value is then calculated from the first and second voltage values measured from the first cardiac electrogram signal. The first voltage value is recorded when the comparison value is greater than or equal to a predetermined value.