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context of haemodynamic instability. When coronary artery disease is suspected, coronary computed tomography (CT), angiography, or stress imaging is recommended.82 Cardiovascular magnetic resonance (CMR) and nuclear imaging techniques provide information on tissue characterization (inflammation, fibrosis/scar) and should be considered before pacemaker implantation when specific aetiologies associated with conduction abnormalities are suspected (specially in young patients). Late gadolinium contrast enhanced (LGE) and T2 CMR techniques allow the diagnosis of specific causes of conduction disturbances (i.e. sarcoidosis and myocarditis). Late gadolinium contrast enhancement CMR helps in the decision-making of individuals with arrhythmic events; the presence of large areas of LGE (scar/fibrosis) has been linked to an increased risk of ventricular arrhythmias regardless of LVEF and may indicate the need for an implantable cardioverter-defibrillator (ICD).8385 T2 CMR sequences are suited for the detection of myocardial inflammation (i.e. oedema and hyperaemia) as a potential cause of transitory conduction abnormalities that may not need permanent pacemaker implantation.86 Similarly, positron emission tomography (PET) combined with CMR or CT helps in the diagnosis of inflammatory activity status of infiltrative cardiomyopathies (i.e. sarcoidosis).87,88

4.3.4 Laboratory tests Laboratory tests, including full blood counts, prothrombin time, partial thromboplastin time, renal function, and electrolyte measurements, are warranted as part of pre-procedural planning for pacemaker implantation. Bradycardia or AVB may be secondary to other conditions (Table 7). When suspected, laboratory data are useful for identifying and treating these conditions (e.g. thyroid function, Lyme titre to diagnose myocarditis in a young person with AVB, endocarditis, hyperkalaemia, digitalis levels, and hypercalcaemia).8994 4.3.5 Genetic testing Most cardiac conduction disorders are due to either ageing or structural abnormalities of the cardiac conduction system caused by underlying structural heart disease. Genes responsible for inherited cardiac diseases associated with cardiac conduction disorders have been identified.65,95,96

Genetic mutations have been linked to a range of abnormalities that may present in isolated forms of cardiac conduction disorder or in association with cardiomyopathy, congenital cardiac anomalies, or extra-cardiac disorders. Most genetically mediated cardiac conduction disorders have an autosomal dominant mode of inheritance65,95 (Supplementary Table 5). Progressive cardiac conduction disease (PCCD) may be diagnosed in the presence of unexplained progressive conduction abnormalities in young (<50 years) individuals with structurally normal hearts in the absence of skeletal myopathies, especially if there is a family history of PCCD.97 Common PCCD-associated genes are SCN5A and TRPM4 for isolated forms and LMNA for PCCD associated with HF. The diagnosis of PCCD in an index patient is based on clinical data including history, family history, and 12-lead ECG. The potential presence of congenital heart disease (CHD) and/or cardiomyopathy must be investigated with cardiac imaging. Early-onset PCCD, either isolated or with concomitant structural heart disease, should prompt consideration of PCCD genetic testing, particularly in patients with a positive family history of conduction abnormalities, pacemaker implants, or sudden death.97 A consensus panel has endorsed mutation-specific genetic testing for family members and appropriate relatives after the identification of a PCCD causative mutation in an index case. Such testing can be deferred in asymptomatic children because of the age-dependent nature of cardiac conduction diseases and incomplete penetrance.65 However, every case should be individually evaluated depending of the risk of the detected mutation. Asymptomatic family members who are positive for the family’s PCCD-associated mutation should be regularly followed for development of cardiac conduction disease-related symptoms, deterioration of cardiac conduction, and beginning of HF.

Recommendations regarding imaging before implantation

Recommendations Classa Levelb

Cardiac imaging is recommended in patients with suspected or documented symptomatic bradycardia to evaluate the presence of structural heart disease, to determine LV systolic function, and to diagnose potential causes of conduction disturbances. I C Multimodality imaging (CMR, CT, or PET) should be considered for myocardial tissue characterization in the diagnosis of specific pathologies associated with conduction abnormalities needing pacemaker implantation, particularly in patients younger than 60 years.8386,88 IIa C

CMR = cardiovascular magnetic resonance; CT = computed tomography; LV = left ventricular; PET = positron emission tomography. aClass of recommendation. bLevel of evidence. Recommendations for laboratory tests

Recommendations Classa Levelb In addition to pre-implantation laboratory tests,c specific laboratory tests are recommended in patients with clinical suspicion for potential underlying causes of reversible bradycardia (e.g. thyroid function tests, Lyme titre, digitalis level, potassium, calcium, and pH) to diagnose and treat these conditions.9094 I C

aClass of recommendation. bLevel of evidence. cComplete blood counts, prothrombin time, partial thromboplastin time, serum creatinine, and electrolytes.

ESC 2021 ESC 2021

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