Abstract: Cardiac systems and methods using ECG and blood information for arrhythmia detection and discrimination. Detection circuitry is configured to produce an ECG. An implantable blood sensor configured to produce a blood sensor signal is coupled to a processor. The processor is coupled to the detection and energy delivery circuitry, and used to evaluate and treat cardiac rhythms using both the cardiac electrophysiologic and blood sensor signals. The blood sensor is configured for subcutaneous non-intrathoracic placement and provided in or on the housing, on a lead coupled to the housing, and/or separate to the housing and coupled to the processor via hardwire or wireless link. The blood sensor may be configured for optical sensing, using a blood oxygen saturation sensor or pulse oximeter. A cardiac rhythm may be evaluated using the electrocardiogram signal and the blood sensor signal, and tachyarrhythmias may be treated after confirmation using the blood sense signal.

Abstract: Systems and methods provide for sensing of cardiac activity from a subcutaneous, non-intrathoracic location, and detecting a cardiac condition necessitating treatment in response to the sensed cardiac activity. One of a number of cardiac therapies may be selectively delivered to treat the detected cardiac condition, such cardiac therapies including at least a tachycardia therapy, a bradycardia therapy, and an asystole prevention therapy.

Abstract: A method and apparatus for assessing the risk of atrial fibrillation in a patient by calculating the relative frequency of short and long intervals between successive heart beats during sinus rhythm is presented. An imbalance of short over long sinus intervals has been found to indicate a higher risk of atrial fibrillation. An implantable cardiac device may be configured to automatically deliver interventional therapy to restore sinus interval balance when such an imbalance is detected.