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........................................................................... system. In addition, genetic mutations have been linked to conduction disorders (see section 4.3.5), and atrial cardiomyopathy23 may be a specific disease that can result in supraventricular tachyarrhythmia, SND, and atrioventricular node (AVN) disease.24

It is essential to differentiate reversible from non-reversible causes of bradycardia. Potential reversible causes of bradycardia include adverse drug effects, myocardial infarction (MI), toxic exposure, infections, surgery, and electrolyte disorders. In a study including 277 patients referred to the emergency department with bradycardia, electrolyte disorders were the underlying cause in 4%, intoxication in 6%, acute MI in 14%, and adverse drug effects in 21%.25 In the case of non-reversible pathological causes of slow heart rate, the presence and severity of symptoms play an essential role in the consideration for permanent antibradycardia pacemaker therapy. This may be challenging in patients with competing mechanisms for their symptoms. In general, candidates for pacing therapy can be broadly classified into two groups: patients with persistent bradycardia and patients with intermittent [with or without electrocardiographic (ECG) documentation] bradycardia. Persistent bradycardia usually indicates an intrinsic disease in the sinus node tissue or the atrioventricular (AV) conduction system, whereas intermittent bradycardia can be a result of a wide variety of intrinsic and extrinsic pathological processes, as illustrated in Figure 2.2631 3.4 Types and modes of pacing: general

description 3.4.1 Endocardial pacing Endocardial lead-based pacemakers consist of a pulse generator commonly placed in the pectoral region and transvenous lead(s) implanted into the myocardium with the ability to sense cardiac activity and provide therapeutic cardiac stimulation. Since the introduction of transvenous endocardial pacemakers in the 1960s, major technological advances have improved their efficacy and safety. In general, pacemaker implantation is considered a low-risk procedure, yet it is not exempt from device- and procedure-related complications and malfunction. Pacemaker implantation is covered in detail in a recent European Heart Rhythm Association (EHRA) consensus document.34

3.4.2 Epicardial pacing Some clinical scenarios dictate implantation of an epicardial pacemaker system. These include patients with congenital anomalies and no venous access to the heart or with an open shunt between the right and left sides of the circulation, recurrent device infections, occluded veins, and—most commonly today—in conjunction with open cardiac surgery. Epicardial leads are currently implanted using various (minimally invasive) thoracotomy or thoracoscopy and robotic techniques.35

Patient with bradycardia-related symptoms

Persistent bradycardia

Y N

Sinus node disease

Documented arrhythmia (ECG/Holter/monitor)

AV block Sinus rhythm Atrial fibrillation

Intrinsic

Paroxysmal AV block Sino-atrial block and sinus arresta Atrial fibrillation with slow ventricular condition

Extrinsic (functional) Vagally induced sinus arrest or AV block Adenosine hypersensitivityb Idiopathic AV block BBB

Reflex syncope

Carotid sinus Tilt-induced

Unexplained syncope

(suspected)

Y

N

Figure 2 Classification of documented and suspected bradyarrhythmias. AV = atrioventricular; BBB = bundle branch block; ECG = electrocardiogram. aIncluding the bradycardiatachycardia form of sick sinus syndrome. bDeharo et al.32 Figure adapted from Brignole et al.33 Downloaded from academic.oup.com/eurheartj/article/42/35/3427/6358547 by guest on 07 October 2026