<unk> s can occur within healthy hearts in response to various stimulating events, such as: * Increased local parasympathetic nervous system activity * Elevated sympathetic nervous system output * Overstimulation from drugs such as caffeine digitalis and catecholamines * Cardiac Ischemia (particularly ventricular ischemia) – the membranes of apoptotic (dying) cells become "leaky" and cause surrounding tissue to become hyperkalemic or hypercalcemic (high concentration of potassium/calcium), causing random excitation. They can also occur within unhealthy hearts, caused by: * Infection * Disease, such as sinus venosis and atrial defects * SA node dysfunction (1st degree block) which can cause the rate of impulse to slow * SA node blockage so that impulses never leave the atria * AV node blockage (3rd degree block) prevents normal conduction across ventricles
Ectopic pacemaker
Wandering atrial pacemaker
Ectopic beat
Junctional ectopic tachycardia
Pre-excitation syndrome
Sinus arrhythmia
Benign early repolarization
Supraventricular tachycardia