An implantable device for monitoring of a patient's electrocardiogram, has a detection element for determining electrocardiogram signals of a heart of the patient. The signals are indicative of the electrocardiogram of the patient. The implantable device includes a processor that is configured to determine from the signals at least one parameter of the electrocardiogram. The at least one parameter is an R:S ratio defined as the ratio between the absolute value of the R complex and the absolute value of the S complex.
