Bradycardia and pacing indications — structured viva

Stem

Practice viva. You are the cardiology registrar. The examiner works through the site of AV block, syncope with conduction disease, sinus node dysfunction, reflex syncope, pacing-induced cardiomyopathy, pacing after surgery, TAVI and MI, leadless pacing and pacing in pregnancy. Answer for an adult unless stated.

Branch A — Where is the block?

Examiner: The strip shows 2:1 AV block. How do you decide where the block is, and why does it matter?^[4]

Strong answer:

• ACC/AHA/HRS 2018: AV block where only 2:1 block is present cannot be classified as Mobitz I or II, so it is important to elucidate the level of block.^[4]
• The site can be AV nodal, intra-Hisian or infra-Hisian; it may be clinically important and can be determined by invasive EPS when it is not apparent from the ECG and clinical circumstances.^[4]
• In general, nodal block is associated with slower progression, a faster and more reliable junctional escape and greater responsiveness to autonomic manipulation such as atropine, isoproterenol and epinephrine; block within or below the His bundle may progress rapidly and unexpectedly, has a slower and more unpredictable escape, and will not respond to atropine but will sometimes improve with catecholamines.^[4]
• ESC 2021 says the nodal versus infranodal distinction may be based on observations such as PR or PP interval prolongation before the block, the effect of exercise on AV conduction, and an EPS.^[1]
• It matters because ESC 2021 paces infranodal 2:1 AVB in sinus rhythm irrespective of symptoms (Class I, Level C), whereas in asymptomatic narrow-QRS 2:1 AVB pacing may be avoided if supra-Hisian block is clinically suspected (concomitant Wenckebach and block that disappears with exercise) or demonstrated at EPS.^[1]

Follow-up: And Mobitz I?^[1]

Answer:

• ESC 2021: supranodal block has a benign course and a low risk of progression to type II or a higher degree of AV block; infranodal block, rare in this form, carries a high risk of progression to complete heart block, syncope and sudden death.^[1]
• Small, retrospective studies have suggested that, over the long term, second-degree type I AVB carries a higher risk of death in patients aged 45 years or older in the absence of pacemaker implantation.^[1]
• Pacing should be considered for second-degree type 1 AVB that causes symptoms or is found to be intra- or infra-His at EPS (Class IIa, Level C).^[1]
• ACC/AHA/HRS 2018: in asymptomatic first-degree, Mobitz I or 2:1 block believed to be at the AV node, permanent pacing should not be performed (COR III: Harm, LOE C-LD).^[4]

Branch B — Syncope with bifascicular block

Examiner: A patient with bifascicular block has unexplained syncope. How do you proceed?^[1]

Strong answer:

• ESC 2021: EPS should be considered when syncope remains unexplained after non-invasive evaluation, or when an immediate decision about pacing is needed due to severity, unless empirical pacemaker implantation is preferred, especially in elderly and frail patients (Class IIa, Level B).^[1]
• A pacemaker is indicated with a baseline HV of 70 ms or more, second- or third-degree intra- or infra-Hisian block during incremental atrial pacing, or an abnormal response to pharmacological challenge (Class I, Level B).^[1]
• The pharmacological stress agents ESC 2021 names are ajmaline, procainamide, flecainide and disopyramide, and an HV of 100 ms or more after pharmacological stress identifies a group at higher risk of developing AVB.^[1]
• In the Scheinman data, which ESC 2021 quotes in its section on bundle branch block, unexplained syncope and abnormal EPS, progression to AVB at 4 years was 4% with HV under 70 ms, 12% with HV 70–100 ms and 24% with HV over 100 ms.^[1]
• ESC 2021 adds that a positive EPS has yielded a positive predictive value as high as 80% for identifying patients who develop AVB.^[1]

Follow-up: And if the EPS is negative?^[1]

Answer:

• A negative EPS cannot rule out intermittent or paroxysmal AVB: in patients with a negative EPS, an implantable loop recorder documented intermittent or stable AVB in about 50%.^[1]
• Pacing may be considered without EPS in selected patients with unexplained syncope and bifascicular block (elderly, frail, high-risk and/or recurrent syncope) (Class IIb, Level B).^[1]
• In elderly patients with bifascicular block and unexplained syncope, ESC 2021 says an empirical pacemaker might be of benefit, especially with unpredictable recurrent syncope and a high risk of traumatic recurrence, decided on individual risk–benefit evaluation.^[1]

Branch C — Sinus node dysfunction

Examiner: When do you pace sinus node dysfunction?^[1]

Strong answer:

• ESC 2021: pacing is indicated in SND when symptoms can clearly be attributed to bradyarrhythmias (Class I, Level B), and in symptomatic patients with the bradycardia–tachycardia form to correct bradyarrhythmias and enable pharmacological treatment, unless ablation of the tachyarrhythmia is preferred (Class I, Level B).^[1]
• Pacing may be considered when symptoms are likely to be due to bradyarrhythmias but the evidence is not conclusive (Class IIb, Level C), and is not recommended for SND bradyarrhythmias that are asymptomatic or due to transient causes that can be corrected and prevented (Class III, Level C).^[1]
• The reason is that, in general, pacing for asymptomatic SND has never been shown to affect prognosis, as opposed to pacing for AVB.^[1]
• With chronotropic incompetence (most commonly defined as failure to reach 80% of the expected heart rate reserve) and clear symptoms during exercise, DDD with rate-responsive pacing should be considered (Class IIa, Level B).^[1]

Follow-up: Which mode, and what is the trial evidence?^[1]

Answer:

• ESC 2021 names DDD(R) as the mode of first choice in SND, with unnecessary RV pacing systematically avoided.^[1]
• In MOST (2010 patients with sinus-node dysfunction, median follow-up 33.1 months), death or nonfatal stroke did not differ significantly between dual-chamber and ventricular pacing (21.5% vs 23.0%, P=0.48), but the risk of AF was lower with dual-chamber pacing (HR 0.79; 95% CI 0.66 to 0.94; P=0.008) and heart-failure scores were better (P<0.001).^[9]
• In DANPACE (1415 patients with sick sinus syndrome referred for first pacemaker implantation, mean follow-up 5.4 years), death was 29.6% with AAIR vs 27.3% with DDDR (HR 1.06, P = 0.53), while paroxysmal AF (28.4% vs 23.0%, HR 1.27, 95% CI 1.03–1.56, P = 0.024) and reoperation (22.1% vs 11.9%, HR 1.99, 95% CI 1.53–2.59, P < 0.001) were more frequent with AAIR; the authors concluded that the findings support the routine use of DDDR pacing in these patients (sick sinus syndrome).^[8]

Branch D — Reflex syncope

Examiner: When is pacing justified in reflex syncope?^[1]

Strong answer:

• ESC 2021 calls pacing the last resort, to be considered only in highly selected patients: over 40 years of age (mostly over 60), with severe reflex syncope and frequent recurrences associated with a high risk of injury, often without a prodrome.^[1]
• Dual-chamber pacing is indicated to reduce recurrent syncope in patients aged over 40 with severe, unpredictable, recurrent syncope who have spontaneous documented symptomatic asystolic pause(s) over 3 s or asymptomatic pause(s) over 6 s due to sinus arrest or AVB, cardioinhibitory carotid sinus syndrome, or asystolic syncope during tilt testing (Class I, Level A).^[1]
• Pacing is not indicated in the absence of a documented cardioinhibitory reflex (Class III, Level B), and dual-chamber pacing may be considered to reduce syncope recurrences in patients with the clinical features of adenosine-sensitive syncope (Class IIb, Level B).^[1]
• For patients aged 40 or under with the same severity criteria, the Task Force could make no recommendation for lack of trial evidence.^[1]

Follow-up: What is the trial evidence for tilt-selected pacing?^[1]

Answer:

• BioSync CLS randomised patients aged 40 years or older with at least two episodes of unpredictable severe reflex syncope during the last year and a tilt-induced syncope with an asystolic pause longer than 3 s to an active (63) or inactive (64) dual-chamber pacemaker with closed loop stimulation, with patients and outcome assessors blinded.^[12]
• After a median 11.2 months, syncope occurred in significantly fewer patients in the pacing group, 10 (16%) vs 34 (53%) (HR 0.23; P = 0.00005), and ESC 2021 upgraded the tilt indication for patients over 40 from IIb to I on such studies.^[12][1]

Branch E — Pacing-induced cardiomyopathy

Examiner: Why worry about right ventricular pacing, and what are the alternatives?^[1]

Strong answer:

• ESC 2021: there is strong evidence that chronic conventional RV pacing may be deleterious in some patients and may lead to LV dysfunction and heart failure, even when AV synchrony is maintained.^[1]
• Pacing-induced cardiomyopathy occurs in 10–20% of patients after 2–4 years of RV pacing and is associated with an RV pacing burden over 20%, although no data support any percentage as a true safe limit.^[1]
• HRS/APHRS/LAHRS 2023 defines cardiac physiologic pacing as pacing intended to restore or preserve ventricular synchrony, including CRT with LV stimulation, His bundle pacing or left bundle branch area pacing.^[5]
• ESC 2026 HF: CRT rather than RV pacing should be considered in HFrEF, regardless of NYHA class or QRS width, with an indication for ventricular pacing for high-degree AV block, to reduce the risk of HF hospitalisation and death (Class IIa, Level B1). An upgrade to CRT should be considered in patients with LVEF 35% or less who have received a conventional pacemaker or an ICD and subsequently develop worsening HF despite optimal foundational medical therapy, and who have a significant proportion of RV pacing, to reduce the risk of HF hospitalisation or death (Class IIa, Level B1).^[2]
• HRS/APHRS/LAHRS 2023: in patients with a CIED and a decline in LV function or worsening HF symptoms attributed to substantial ventricular pacing, CRT with biventricular pacing is recommended to improve LV function and HF symptoms (COR 1, LOE B-NR), and revision of the CIED to a CSP device can be beneficial to improve LV function and symptoms of HF (COR 2a, LOE B-NR).^[5]

Follow-up: Where does left bundle branch area pacing stand?^[1]

Answer:

• ESC 2021 described the lead as implanted slightly distal to the His bundle and screwed deep into the LV septum, ideally to capture the left bundle branch, but with scarce data and concern about long-term lead performance and extraction it could not formulate recommendations.^[1]
• The 2025 ESC consensus statement, a consensus document rather than a guideline, notes that CSP use has greatly evolved since 2021, mainly with LBBAP.^[6]
• It advises LBBAP over HBP with significant aortic valve disease (which may require future intervention), infranodal AV block or AV node ablation, and HBP over LBBAP when the tricuspid valve must be spared.^[6]
• HRS/APHRS/LAHRS 2023 says an LBBAP lead may be considered as an alternative to an RV lead with normal LVEF and less than substantial anticipated ventricular pacing (COR 2b, LOE C-LD).^[5]

Branch F — After surgery, TAVI and myocardial infarction

Examiner: Complete AV block appears on day 1 after valve surgery. When do you implant a permanent pacemaker?^[1]

Strong answer:

• ESC 2021: with high-degree or complete AVB after cardiac surgery, a period of clinical observation of at least 5 days is indicated to assess whether the rhythm disturbance is transient and resolves, but with complete AVB and low or no escape rhythm when resolution is unlikely the period can be shortened (Class I, Level C).^[1]
• Complete AVB in the first 24 h after valvular surgery that persists for 48 h is unlikely to resolve in the next 1–2 weeks, so earlier implantation may be considered.^[1]
• The ideal timing of implantation after cardiac surgery is controversial because 60–70% of patients implanted for SND and up to 25% of those implanted for AVB are not pacemaker dependent at follow-up.^[1]
• For surgery in infective endocarditis, the 2023 ESC endocarditis guideline states that immediate epicardial pacemaker implantation should be considered in patients undergoing surgery for valvular IE and complete AVB if one of the following predictors of persistent AVB is present: pre-operative conduction abnormality, Staphylococcus aureus infection, aortic root abscess, tricuspid valve involvement, or previous valvular surgery (Class IIa, Level C).^[14]
• After mechanical tricuspid valve replacement, a transvalvular RV lead should be avoided (Class III, Level C).^[1]

Follow-up: How does the timing differ after TAVI and after myocardial infarction?^[1][3][13]

Answer:

• After TAVI, ESC 2021 recommends permanent pacing for complete or high-degree AVB that persists for 24–48 h (Class I, Level B) and for new-onset alternating BBB (Class I, Level C).^[1]
• After MI, ESC 2023 recommends a permanent pacemaker when high-degree AV block does not resolve within a waiting period of at least 5 days (Class I, Level C), and pacing is not recommended if the block resolves after revascularisation or spontaneously (Class III, Level B).^[3]
• In the US, the supportive text of the 2025 ACC/AHA ACS guideline states that permanent pacemaker insertion is recommended with unresolved high-degree AV block that persists over 72 hours; no class is given because this is supportive text.^[13]

Branch G — Leadless pacing and pregnancy

Examiner: When would you choose a leadless pacemaker?^[1]

Strong answer:

• ESC 2021: leadless pacemakers should be considered as an alternative to transvenous pacemakers when no upper extremity venous access exists or when the risk of device pocket infection is particularly high, such as previous infection and patients on haemodialysis (Class IIa, Level B), and may be considered as an alternative to standard single-lead ventricular pacing, taking life expectancy into consideration and using shared decision-making (Class IIb, Level C).^[1]
• VVI(R)-only devices restrict indications to AF or very infrequent pacing (e.g. paroxysmal AVB); VDD leadless pacing extends indications to AVB with preserved sinus node function.^[1]
• There are no RCT data on the long-term safety and efficacy of leadless versus standard transvenous pacemakers, so the indication should be carefully considered case by case.^[1]
• The absence of long-term performance data and the limited data on retrievability and end-of-life strategy also require careful consideration before choosing a leadless pacemaker, especially in younger patients (e.g. life expectancy over 20 years).^[1]

Follow-up: A woman with congenital complete heart block is pregnant. Does she need a pacemaker?^[1]

Answer:

• ESC 2021: with a slow, wide-QRS escape rhythm she should undergo pacemaker implantation during pregnancy.^[1]
• With a stable, narrow-complex junctional escape and none of the risk factors (syncope, pauses over 3 times the cycle length of the ventricular escape rhythm, wide QRS escape rhythm, prolonged QT interval, complex ventricular ectopy, mean daytime heart rate below 50 b.p.m.), implantation may not be necessary or can be deferred until after delivery.^[1]
• Implantation risks are generally low, especially beyond 8 weeks of gestation, and a pacemaker for symptomatic bradycardia can be implanted at any stage of pregnancy using echo guidance or electroanatomic navigation to minimise fluoroscopy.^[1]
• The 2025 ESC pregnancy guideline states that pacing indications (temporary and permanent) do not differ between pregnant and non-pregnant women, and that if a pacemaker is indicated during pregnancy, implantation is recommended with optimal radiation protection (Class I, Level C).^[15]
• For delivery, it says vaginal delivery does not cause extra risk for mothers who are asymptomatic, haemodynamically stable and have a normal cardiac anatomy and function; in asymptomatic congenital AV block with normal cardiac anatomy and function, a narrow QRS complex and ventricular rate of 50 b.p.m. or more, a prophylactic temporary pacemaker during delivery is not recommended (Class III, Level C).^[15]