An active implantable medical device of the single-chamber implantable defibrillator/cardioverter type, comprising: - a single-body lead, with a lead body carrying: • a defibrillation electrode in the form of a ventricular coil arranged on the body so as to be positioned in the ventricle once the lead implanted, forming a first shock electrode and a first electrode for depolarization signal detection; • a defibrillation electrode in the form of a supraventricular coil arranged on the body so as to be positioned in the superior vena cava once the lead implanted, forming a second shock electrode and a second electrode for depolarization signal detection; and • a distal electrode forming a third electrode for depolarization signal detection, - an implantable generator, including: • a metal case forming a reference potential electrode; • circuits for analysing the signals collected by said detection electrodes, comprising: - means for collecting a first unipolar signal between the ventricular coil and the generator case, - means for collecting a second unipolar signal between the supraventricular coil and the generator case; and - ICA analysis means adapted to discriminate statistically independent source signals by an Independent Component Analysis; and • circuits for delivering anti-tachycardia therapies, the device being characterized in that: - the lead is devoid, at the atrium, of a specific electrode for atrial signal collection, and - the generator comprises atrial activity signal estimator means, including said ICA analysis means, these ICA analysis means being adapted to operate an ICA analysis between said first and second unipolar signals and to output a first source signal representative or said atrial activity, separated by the ICA analysis from a second source signal representative of a ventricular activity. - a single-body lead, with a lead body carrying: • a defibrillation electrode in the form of a ventricular coil arranged on the body so as to be positioned in the ventricle once the lead implanted, forming a first shock electrode and a first electrode for depolarization signal detection; • a defibrillation electrode in the form of a supraventricular coil arranged on the body so as to be positioned in the superior vena cava once the lead implanted, forming a second shock electrode and a second electrode for depolarization signal detection; and • a distal electrode forming a third electrode for depolarization signal detection, • a defibrillation electrode in the form of a ventricular coil arranged on the body so as to be positioned in the ventricle once the lead implanted, forming a first shock electrode and a first electrode for depolarization signal detection; • a defibrillation electrode in the form of a supraventricular coil arranged on the body so as to be positioned in the superior vena cava once the lead implanted, forming a second shock electrode and a second electrode for depolarization signal detection; and • a distal electrode forming a third electrode for depolarization signal detection, - an implantable generator, including: • a metal case forming a reference potential electrode; • circuits for analysing the signals collected by said detection electrodes, comprising: - means for collecting a first unipolar signal between the ventricular coil and the generator case, - means for collecting a second unipolar signal between the supraventricular coil and the generator case; and - ICA analysis means adapted to discriminate statistically independent source signals by an Independent Component Analysis; and • circuits for delivering anti-tachycardia therapies, • a metal case forming a reference potential electrode; • circuits for analysing the signals collected by said detection electrodes, comprising: - means for collecting a first unipolar signal between the ventricular coil and the generator case, - means for collecting a second unipolar signal between the supraventricular coil and the generator case; and - ICA analysis means adapted to discriminate statistically independent source signals by an Independent Component Analysis; and - means for collecting a first unipolar signal between the ventricular coil and the generator case, - means for collecting a second unipolar signal between the supraventricular coil and the generator case; and - ICA analysis means adapted to discriminate statistically independent source signals by an Independent Component Analysis; and • circuits for delivering anti-tachycardia therapies, - the lead is devoid, at the atrium, of a specific electrode for atrial signal collection, and - the generator comprises atrial activity signal estimator means, including said ICA analysis means, these ICA analysis means being adapted to operate an ICA analysis between said first and second unipolar signals and to output a first source signal representative or said atrial activity, separated by the ICA analysis from a second source signal representative of a ventricular activity.