Implantable cardioverter/defibrillator employing shock delivery timing for preventing induced fibrillation

An implantable cardioverter/defibrillator which applies a quantity of electrical energy to a heart to terminate a ventricular arrhythmia without inducing atrial fibrillation, the cardioverter/defibrillator comprising:

• a ventricular arrhythmia detector,
• an atrial activation detector;
• timing circuitry that defines a vulnerable period in response to an atrial activation detected by the atrial activation detector;
• and
• a generator that delivers the quantity of electrical energy to the heart responsive to the ventricular arrhythmia detector detecting a ventricular arrhythmia and at a predetermined time after detection of an atrial activation, wherein the predetermined time is selected to avoid the vulnerable period.

A method of applying a quantity of electrical energy to a heart to terminate a ventricular arrhythmia, the method including the steps of:

• detecting a ventricular arrhythmia of the heart;
• detecting an atrial activation;
• defining a vulnerable period related to the atrial activation;
• and
• delivering the quantity of electrical energy to the heart after detecting the ventricular arrhythmia and at a predetermined safe time after detecting an atrial activation which avoids the vulnerable period.