Pacemaker

An artificial cardiac pacemaker is a medical device implanted or applied to regulate the electrical conduction system of the human heart. It generates precisely timed electrical impulses that are delivered to one or more heart chambers through electrodes. These impulses trigger myocardial contraction and ensure an adequate and regular heart rate. Pacemakers are used when the heart’s intrinsic rhythm becomes insufficient or irregular, commonly due to sinoatrial node disease, atrioventricular block, or other disturbances of cardiac conduction. Modern systems are externally programmable, enabling clinicians to tailor pacing modes to patient requirements. Most devices operate in an on-demand fashion, initiating impulses only when intrinsic cardiac activity falls below a predetermined threshold.

Background and Clinical Purpose

Pacemakers serve to correct bradyarrhythmias, maintain synchronous cardiac chamber activity, and prevent haemodynamic instability. Their use is established in conditions such as symptomatic bradycardia, heart block, and sick sinus syndrome. Specialised forms, including implantable cardioverter-defibrillators, perform both pacing and defibrillation functions, while cardiac resynchronisation therapy devices coordinate ventricular contraction to improve efficiency in heart failure. The evolution of pacemakers from external, fixed-rate machines to highly sophisticated, programmable systems has markedly improved clinical outcomes.

Methods of Cardiac Pacing

Various techniques are used to stimulate cardiac activity depending on the clinical scenario, urgency, and intended duration of therapy.
Percussive pacing
Percussive pacing, also termed transthoracic mechanical pacing, is a temporary emergency method used when electrical pacing is unavailable. A closed fist is applied to the left lower edge of the sternum, overlying the right ventricle, and delivered from a height of approximately 20–30 cm. The British Journal of Anaesthesia notes that generating a ventricular pressure of around 10–15 mmHg can stimulate electrical activity. This technique is reserved exclusively for life-saving situations and is employed only until proper electrical pacing becomes accessible.
Transcutaneous pacing
Transcutaneous pacing is a non-invasive emergency procedure indicated for the stabilisation of significant bradycardias. Two external pacing pads are placed in either the anterior–lateral or anterior–posterior configuration. The operator sets a pacing rate and gradually increases the current until electrical capture is achieved, demonstrated on an electrocardiogram by a wide QRS complex with an associated pulse. Muscle contractions and pacing artefacts can make confirmation challenging. As the method is uncomfortable and unsuitable for prolonged use, it acts as a bridge to more definitive modalities such as transvenous pacing.
Epicardial pacing
Epicardial pacing is commonly used during or following cardiac surgery, especially where temporary atrioventricular block may occur. Electrodes are attached directly to the epicardium, maintaining adequate cardiac output until a transvenous system is placed or intrinsic conduction returns. Permanent epicardial leads may be surgically implanted and tunnelled to a generator pocket. These leads can be fixed passively by suturing or actively via screw mechanisms.
Temporary transvenous pacing
Temporary transvenous pacing involves introducing a pacing wire into a central vein under sterile conditions and advancing it into the right atrium or right ventricle. Connected to an external generator, this method is more reliable than transcutaneous pacing and is used as a bridge to permanent implantation or until pacing is no longer required.

Permanent Transvenous Pacemakers

Permanent pacemaker implantation involves placing one or more pacing leads transvenously into specific cardiac chambers, guided by fluoroscopy. After positioning is verified, the leads are connected to a generator, which is implanted subcutaneously beneath the clavicle. Titanium is frequently used for generator casing due to its biocompatibility.
The principal types of permanent pacemakers include:

• Single-chamber pacemakers – One lead is placed in either the atrium or ventricle. This approach is suitable where pacing is required for a single chamber only.
• Dual-chamber pacemakers – Leads are placed in both the atrium and the ventricle to coordinate atrioventricular activity, offering a rhythm closer to natural cardiac physiology.
• Biventricular pacemakers – Used in cardiac resynchronisation therapy, these devices position leads in the atrium and both ventricles, improving the synchrony of ventricular contraction.
• Rate-responsive pacemakers – These devices contain sensors that detect physiological changes, such as movement or respiration, and adjust the pacing rate to meet metabolic demands.

Leadless Pacemakers

Leadless pacemakers represent a significant technological development. These capsule-sized devices contain both the generator and electrodes and are placed entirely within the heart via a catheter introduced through the femoral vein. By eliminating leads, they avoid common complications such as lead fracture or venous obstruction. Their design offers an attractive alternative for selected patients, although they are generally limited to single-chamber ventricular pacing.

Basic Function and Pacing Modes

Modern pacemakers continuously monitor intrinsic cardiac electrical activity. When no natural impulse is detected within a programmed interval, the device emits a low-voltage pulse to initiate contraction. If intrinsic activity occurs, pacing is inhibited. This process is termed demand pacing.
Different modes are tailored to specific clinical needs:

• VVI / VVIR – Ventricular demand pacing, with or without rate responsiveness, used when atrial synchrony is unnecessary, such as in atrial fibrillation.
• AAI / AAIR – Atrial demand pacing for patients with intact atrioventricular conduction but unreliable sinoatrial node function.
• VDD – A single lead with multiple electrodes senses atrial activity and paces the ventricle following an appropriate delay; useful in atrioventricular block.
• DDDR – A dual-chamber system capable of sensing and pacing both chambers, providing the most comprehensive functionality. It requires meticulous programming to achieve optimal performance.