Pacemaker: permanent

A permanent pacemaker (PPM) is an electronic device that maintains a consistent and physiologically adequate heart rate when the natural cardiac pacemaker system fails.

Background Anatomy/physiology

Electrical impulses originate from the sinoatrial (SA) node in the right atrium, leading to atrial contraction. The impulse then travels to the atrioventricular (AV) node and subsequently along the Purkinje fibres, culminating in ventricular contraction. This coordinated activity results in an effective cardiac output.

Dysfunction at any level of this conduction system can result in arrhythmias. A PPM, once implanted, helps to rectify these abnormalities by delivering timed electrical stimuli to the myocardium, promoting effective contractions and thereby maintaining circulation.

Indications

Permanent pacemaker insertion may be indicated after potentially reversible causes of bradycardia have been excluded.

• symptomatic sinus node dysfunction, including sick sinus syndrome, sinus pauses, chronotropic incompetence and bradycardia–tachycardia syndrome
• persistent symptomatic bradycardia, including atrial fibrillation with a slow ventricular response
• Mobitz type II, high-grade or complete AV block, even in the absence of symptoms
• persistent high-grade or complete AV block following myocardial infarction, cardiac surgery or transcatheter aortic valve implantation
• selected patients with recurrent syncope due to conduction disease or documented asystole, for example:
• alternating bundle branch block or syncope with bifascicular block and evidence of infranodal disease
• patients aged over 40 years with severe recurrent reflex syncope and a documented symptomatic pause > 3 seconds or asymptomatic pause > 6 seconds

Asymptomatic sinus bradycardia, first-degree AV block and asymptomatic Mobitz type I AV block do not usually require permanent pacing.

Classification and types

Nomenclature of pacemakers

There is a standard code to describe the functions of a pacemaker in a systematic and concise manner. Each position in the code denotes a specific characteristic of the pacemaker's function. The code typically consists of three to five positions.

• V - Ventricle
• A - Atrium
• D - Dual (both atrium and ventricle)
• O - None (no pacing)

• V - Ventricle
• A - Atrium
• D - Dual (both atrium and ventricle)
• O - None (no sensing)

• I - Inhibited (pacemaker is prevented from pacing if it senses intrinsic cardiac activity)
• T - Triggered (pacemaker will release a pulse if it senses intrinsic activity, usually used in combination therapies)
• D - Dual (both inhibited and triggered)
• O - None (no response to sensing)

For pacemakers with more advanced functionalities, there are often fourth and fifth positions:

• R - Rate modulated (the pacemaker can adjust its pacing rate in response to changes in the patient's activity or other physiological indicators)
• O - None (no rate modulation)

• A - Atrium
• V - Ventricle
• D - Dual (both atrium and ventricle)
• O - None (no multi-site pacing)

• VVI: A pacemaker that paces the ventricle, senses the ventricle, and will be inhibited if it detects an intrinsic ventricular beat.
• AAI: A pacemaker that paces the atrium, senses the atrium, and will be inhibited if it detects an intrinsic atrial beat.
• DDD: A pacemaker that paces and senses in both the atrium and ventricle. It can both inhibit and trigger pacing based on its sensing.
• VVIR: A ventricular paced, ventricular sensed, inhibited response pacemaker that can adjust its rate based on physiologic demand.

Types of pacemaker

Permanent pacemakers come in various configurations based on their lead placement, the number of chambers they interact with, and their specific functionalities.

• Ventricular (VVI) pacemaker: This is the most common type of single-chamber pacemaker. The lead is placed in the ventricle (typically the right ventricle), and it both senses and paces in that chamber. It is particularly useful for patients with atrial fibrillation and AV block.
• Atrial (AAI) pacemaker: Less common than VVI, this pacemaker's lead is placed in the atrium (usually the right atrium). It senses and paces the atrium and is primarily used in patients with sinus node dysfunction without AV block.

• This type places leads in both the right atrium and right ventricle. It can sense and pace in both chambers, allowing for more physiological pacing by preserving the natural sequence of atrial and ventricular contraction. This is particularly beneficial for patients with sinus node dysfunction and AV block.

• These pacemakers adjust the pacing rate based on physiological demand. They use various sensors, such as those detecting motion or respiratory rate, to gauge the patient's activity level and adjust pacing accordingly. Both single-chamber (AAIR or VVIR) and dual-chamber (DDDR) pacemakers can be rate-responsive.

• These are specialised devices used primarily for heart failure patients with ventricular dyssynchrony. In addition to the standard right atrium and right ventricle leads, they have a lead placed on the outer surface of the left ventricle, allowing for simultaneous pacing of both ventricles. This can enhance cardiac performance in selected patients by ensuring that the two ventricles contract synchronously.
• Some CRT devices also incorporate defibrillation capabilities (CRT-D) and can deliver shocks if a life-threatening ventricular arrhythmia is detected.