The number of leads vary depending on the number of chambers of the heart that need to be treated. A pacemaker can have 1, 2 or 3 leads. Some modern pacemakers do not have leads in order to deliver the electrical signals to the heart muscles. These pacemakers are called leadless.
Single chamber pacemaker
A single chamber pacemaker has only one electrode, which means that it delivers electrical impulses in only one chamber of the heart. The electrode can be placed in the right atrium of the heart (when the electrical signals begin in sinus node, but are slow) or in the right ventricle (when the heart rhythm is slow, but it does not begin in the sinus node, e.g. in cases of atrial fibrillation).
Dual chamber pacemaker
A dual chamber pacemaker has two leads which deliver electrical impulses to the right atrium and to the right ventricle of the heart. A dual chamber pacemaker is used when the electrical signals are blocked between the atrium and the ventricle (AV block) and it helps to coordinate the contraction of these two chambers.
A biventricular pacemaker, also called cardiac resynchronization therapy (CRT) has two or three electrodes, which deliver the electrical impulses to the right ventricle, left ventricle and right atrium. When the rhythm of the heart is atrial fibrillation, no electrode in the right atrium is required.
The role of a CRT device is to coordinate the contraction of the right and left ventricles, making each heartbeat more efficient.
Leadless pacemakers are small devices which consist of a pulse generator only, they have no leads. They are placed through the femoral vein at the top of the leg up into the right ventricle of the heart. They deliver electrical impulses through direct contact with the heart muscle. A leadless pacemaker can be used to stimulate only one chamber of the heart, the right ventricle. It is therefore restricted to those patients who only require single chamber pacing of the right ventricle.