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............................................................... In patients with AF, compared with fixed rate pacing, rateresponsive pacing is associated with better exercise performance, improved daily activities, a decrease in symptoms of shortness of breath, chest pain, and palpitations, and improved quality of life.201203 It has also been shown to improve heart rate and blood pressure response to mental stress compared with fixed rate pacing.204 Therefore, rate-adaptive pacing is the pacing mode of first choice. Fixed-rate VVI pacing should be reserved for older sedentary patients who have very limited activity. Commonly, the minimum rate is programmed higher (e.g. 70 b.p.m.) than for patients in SR in an attempt to compensate for loss of active atrial filling.

5.3 Pacing for conduction disorders

without atrioventricular block This section focuses on patients with 1:1 AV conduction and QRS abnormalities caused by delayed or blocked conduction of the HisPurkinje system: BBB, fascicular block in isolation or in combination with BBB, and non-specific intraventricular delay. Bifascicular block is defined as LBBB or the combination of RBBB and with left anterior or posterior fascicular block. Isolated fascicular block and BBB are rarely associated with symptoms; however, their presence may be a marker for underlying structural heart disease. The presence or absence of symptoms referable to intermittent bradycardia will guide the evaluation of these patients.

5.3.1 Indications for pacing 5.3.1.1 Bundle branch block and unexplained syncope Although syncope is not associated with an increased incidence of sudden death in patients with preserved cardiac function, a high incidence of total deaths (about one-third sudden) was observed in patients with BBB and HF, previous MI, or low EF.208210 Indeed, in those with low EF, syncope is a risk factor for death.211 Unfortunately, ventricular-programmed stimulation does not seem to identify these patients correctly; therefore, an ICD or a defibrillator with CRT (CRT-D) is indicated in patients with BBB and LVEF <35% for the prevention of SCD (Figure 6).63

5.3.1.2 Bundle branch block, unexplained syncope, and abnormal electrophysiological study Electrophysiological assessment includes measurement of the HV at baseline, with stress by incremental atrial pacing or by

Decision algorithm for patients with unexplained syncope and BBB

Bifascicular block

LVEF ≤ 35%

Elderly and frail patients

at risk of traumatic

recurrrences

ICD/CRT-D Clinical follow-up Adapted therapy Pacemaker implant

EPS/CSM

ILR

N

N

No diagnosis

Y

Y

Diagnosis

No diagnosis Diagnosis

Figure 6 Decision algorithm for patients with unexplained syncope and bundle branch block. BBB = bundle branch block; CRT-D = defibrillator with cardiac resynchronization therapy; CSM = carotid sinus massage; EPS = electrophysiology study; ICD = implantable cardioverter-defibrillator; ILR = implantable loop recorder; LVEF = left ventricular ejection fraction. Downloaded from academic.oup.com/eurheartj/article/42/35/3427/6358547 by guest on 07 October 2026