Cardiac Pacemakers
Pacemakers are an electronic device that are used to maintain and control the rate and rhythm of a patients heart beat. They are used to treat abnormal rhythms (arrhythmias) that are either too fast, too slow, or irregular. Ultimately, they keep the chambers of the heart beating at the appropriate time to ensure adequate flow through the heart. They can be temporary or permanent, depending on the indication for its use. If permanent, the pacemaker device will be placed in the chest wall. The leads of the pacemaker travel through the subclavian vein and into the superior vena cava. They ultimately attach to the right atrium, right ventricle, and at times the left ventricle.
There are three major components to a pacemaker: (1) the pulse generator, (2) leads/wires, (3) electrodes. The pulse generator sits outside of the heart and creates the electrical energy for the pulse. The leads travel through the venous structures, carrying the pulses to the heart. And the electrodes live in the atrium or ventricle and detect your hearts natural heartbeat and delivery the pulse.
There are 10 Class I and Class II Indications for a permanent pacemaker implantation. The most common reasons include sinus node dysfunction and high grade atrioventricular (AV) block. The total list of indications include:
Sinus node dysfunction
Acquired AV Block
Chronic bifascicular block
After acute phase of myocardial infarction
Neurocardiogenic syncope and hypersensitive carotid sinus syndrome
Post cardiac transplantation
Hypertrophic cardiomyopathy
Pacing to detect and terminate tachycardia
Cardiac resynchronization therapy in patients with severe systolic heart failure
Patients with congenital heart disease
When evaluating a patient with a pacemaker, the first thing you want to figure out is what mode the pacemaker is in. The North American Society for Pacing and Electrophysiology (NAPSE) and British Pacing and Electrophysiology Group (BPEG) created a 5 Position Code to describe the function of a pacemaker setting.
Position I refers to the chambers that are being paced. This can be denoted with 4 letters: O, A, V, or D. O means no chambers are being paced. A means the atrium is being paced. V means the ventricle is being paced. And D means both the atrium and ventricle can be paced.
Position II refers to the chamber being sensed. Again, this is denoted with 4 letters: O (none), A (atrium), V (ventricle), or D (dual, A+V). O in this case would refer to an “asynchronous” pacing mode.
Position III refers to the pulse generators response to a sensed event. The letters denoted here are O (none), T (trigger), I (inhibit), and D (dual, T+I). T will trigger a pulse based on an event that is sensed. I will inhibit a pulse based on what is being sensed.
Position IV refers to rate modulation. This can be denoted with O (none) or R (rate modulation). This refers to a pacemaker that can sense mechanical vibration, minute ventilation, or acceleration, leading the pacemaker to adjust its response to this stress. A classic example would be a rate modulation in response to exercise.
Position V refers to multisite pacing. This can be denoted with an O (none), A (atrium), V (ventricle), or D (dual, A+V) as well. This will tell you the presence and location of multisite pacing when medically necessary for a patient.
