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................................................................................... 4.3.1 Ambulatory electrocardiographic monitoring The intermittent nature of most symptomatic bradycardia secondary to conduction system disease often requires prolonged ambulatory ECG monitoring to correlate rhythm disturbances with symptoms. This monitoring allows detection of interruption of AV conduction by either primary disease of the conductive system, a vagal or neurocardiogenic mechanism, or reflex AV block.72,72a

Ambulatory ECG identifies defects of sinus automaticity, which includes sinus pauses, sinus bradycardia, bradycardiatachycardia syndrome, asystole post-conversion of atrial flutter or AF, and chronotropic incompetence. Different versions of ambulatory ECG monitoring have been reviewed recently in a comprehensive expert consensus (Supplementary Table 4).73 Ambulatory ECG selection depends on the frequency and nature of the symptoms (Table 8).

4.3.2 Exercise testing Exercise testing may be useful in selected patients with suspected bradycardia during or shortly after exertion. Symptoms occurring during exercise are likely to be due to cardiac causes, whereas symptoms occurring after exercise are usually caused by a reflex mechanism. Exercise testing can be used to diagnose symptomatic chronotropic incompetence, defined as an inability to increase the heart rate commensurate with the increased metabolic demands of physical activity.74,75 The most commonly used definition of chronotropic incompetence has been failure to reach 80% of the expected heart rate reserve. Expected heart rate reserve is defined as the difference between the age-predicted maximal heart rate (220  age) and the resting heart rate. However, some medical treatments and comorbidities cause exercise intolerance and make the diagnosis of chronotropic incompetence by exercise testing more difficult.

In patients with exercise-related symptoms, the development or progression of AVB may occasionally be the underlying cause. Tachycardia-related exercise-induced second-degree and complete AVB have been shown to be located distal to the AVN and predict progression to permanent AVB.7678 Usually, these patients show intraventricular conduction abnormalities on the resting ECG, but a normal resting ECG has also been described in such cases.77,79 Exercise testing may expose advanced infranodal AVB in the presence of conduction system disease of uncertain location. In rare cases, conduction disturbances induced by exercise are caused by myocardial ischaemia or coronary vasospasm, and exercise testing may reproduce the symptoms.80,81 There are no data supporting an indication for exercise testing in patients without exercise-related symptoms. Exercise testing may be useful in selected patients to distinguish AVN from conduction disturbances in the HisPurkinje system below the AVN in the setting of conduction disturbance at an unclear level.

4.3.3 Imaging In patients with suspected or documented symptomatic bradycardia, the use of cardiac imaging is recommended to evaluate the presence of structural heart disease, to determine LV systolic function, and to diagnose potential reversible causes of conduction disturbances (Table 7). Echocardiography is the most commonly available imaging technique for evaluation of the above factors. It can also be used in the

Table 8 Choice of ambulatory electrocardiographic monitoring depending on symptom frequency

Frequency of symptom Daily 24-h Holter ECG or in-hospital telemetric

monitoring

Every 4872 h 244872 h Holter ECG Every week 7-day Holter ECG/external loop recorder/ external patch recorder Every month External loop recorder/external patch

recorder/handheld ECG recorder

<1 per month ILR ECG = electrocardiogram; ILR = implantable loop recorder. Adapted from Brignole et al.33 ESC 2021

Recommendation for ambulatory electrocardiographic monitoring

Recommendation Classa Levelb

Ambulatory ECG monitoring is recommended in the evaluation of patients with suspected bradycardia to correlate rhythm disturbances with symptoms.73 I C

ECG = electrocardiogram. aClass of recommendation. bLevel of evidence. ESC 2021 Recommendations for exercise testing

Recommendations Classa Levelb

Exercise testing is recommended in patients who experience symptoms suspicious of bradycardia during or immediately after exertion.62,7480 I C In patients with suspected chronotropic incompetence, exercise testing should be considered to confirm the diagnosis.74,75 IIa B In patients with intraventricular conduction disease or AVB of unknown level, exercise testing may be considered to expose infranodal block.76,77,79 IIb C

AVB = atrioventricular block. aClass of recommendation. bLevel of evidence. ESC 2021

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