In a patient with type 2 diabetes and a tendency toward bradycardia, can sinus bradycardia with intermittent type I (Wenckebach) AV block cause dizziness?

Can Sinus Bradycardia with Occasional Wenckebach Cause Dizziness?

Yes, sinus bradycardia with intermittent type I (Wenckebach) AV block can absolutely cause dizziness, particularly when it occurs frequently or during exercise. 1

Evidence from Guidelines

The 2018 ACC/AHA/HRS guideline explicitly states that second-degree atrioventricular block type I (Wenckebach) can cause symptoms of exertional intolerance or dizziness when occurring frequently or during exercise, even though it is often asymptomatic in healthy individuals. 1

The key determinants of whether symptoms occur are:

• Frequency of occurrence – Occasional episodes may be asymptomatic, but frequent episodes increase the likelihood of symptoms 1
• Ventricular rate during episodes – Lower resulting heart rates produce more symptoms 1
• Timing relative to activity – Wenckebach occurring during exercise is more likely to cause symptoms than at rest 1

Mechanism of Dizziness

Dizziness occurs when the combination of baseline sinus bradycardia plus intermittent Wenckebach block reduces cardiac output below the threshold needed to maintain adequate cerebral perfusion. 2, 3

• The dropped beats during Wenckebach episodes transiently lower the ventricular rate further, causing brief periods of cerebral hypoperfusion that manifest as dizziness or presyncope 2, 3
• In patients with diabetes (as in your expanded context), autonomic dysfunction may impair compensatory mechanisms, making symptoms more likely 4, 5

Clinical Assessment Algorithm

Step 1: Establish Symptom-Rhythm Correlation

• Document the bradycardia and Wenckebach episodes on ECG or ambulatory monitoring 1
• For daily symptoms: 24-72 hour Holter monitor (Class I) 1
• For weekly symptoms: 7-30 day event recorder (Class I) 1
• Correlation between documented bradycardia/Wenckebach and dizziness is the gold standard before attributing symptoms to the rhythm 1

Step 2: Identify and Treat Reversible Causes (Class I Priority)

Before any intervention, systematically evaluate:

Reversible Cause	Evaluation	Treatment
Medications (β-blockers, calcium-channel blockers, digoxin, amiodarone)	Review drug list	Discontinue or reduce dose [1]
Hypothyroidism	TSH, free T4	Levothyroxine replacement [1]
Electrolyte abnormalities	Serum K⁺, Mg²⁺	Correct imbalances [1]
Obstructive sleep apnea	Clinical screen, sleep study	CPAP therapy [4]
Acute myocardial infarction (especially inferior)	Troponin, ECG	Treat ischemia [1]

In the case report by Herz (2008), a patient with symptomatic sinus bradycardia and Wenckebach was successfully treated with CPAP for sleep apnea rather than pacemaker implantation, demonstrating the critical importance of identifying reversible causes. 4

Step 3: Determine Need for Permanent Pacing

Permanent pacemaker implantation is indicated (Class I) when symptomatic bradycardia with Wenckebach persists after reversible causes have been excluded or adequately treated. 1, 6

However, if the Wenckebach is truly occasional and asymptomatic, no treatment is required (Class III – not indicated). 1, 6

Special Consideration: Vagally-Mediated vs. Intrinsic Disease

A critical distinction must be made between benign vagally-mediated Wenckebach and intrinsic conduction disease:

• Vagally-mediated block occurs with sinus slowing (especially at night or with vagal maneuvers), has normal baseline AV conduction, and carries a benign prognosis 6, 5, 7
• Intrinsic AV disease shows abnormal baseline conduction (prolonged PR, bundle branch block), occurs spontaneously or with exercise, and has high risk of progression to complete heart block 6

In one study of hypervagotonic sinus node dysfunction, 78% of patients were successfully managed with theophylline rather than pacemaker, with only one patient requiring pacing during 43-month follow-up. 5

Common Pitfalls to Avoid

• Do not assume occasional Wenckebach is always benign – frequency and symptom correlation are critical 1
• Do not implant a pacemaker before fully evaluating reversible causes, especially sleep apnea in patients with diabetes and obesity 4
• Do not attribute dizziness to Wenckebach without documented rhythm-symptom correlation 1
• Do not overlook medication review – beta-blockers and calcium-channel blockers are common culprits in diabetic patients 1