In an elderly patient with hypertension and diabetes, the ECG shows loss of P waves with an irregularly irregular rhythm and a slow, regular ventricular rate suggesting atrial fibrillation with high‑grade atrioventricular block; what is the diagnosis and how should it be managed?

Atrial Fibrillation with High-Grade Atrioventricular Block

This ECG pattern showing absent P waves with an irregularly irregular baseline (atrial fibrillation) combined with a slow, regular ventricular rate represents atrial fibrillation complicated by high-grade or complete atrioventricular block—a life-threatening condition requiring immediate exclusion of reversible causes followed by urgent permanent pacemaker implantation. 1, 2

Diagnostic Confirmation

The ECG demonstrates two simultaneous pathologies that create a distinctive pattern:

• Atrial fibrillation is confirmed by the complete absence of organized P waves, replaced by fibrillatory waves, with an irregularly irregular atrial baseline 1
• High-grade or complete AV block is indicated by the paradoxically slow and regular ventricular rate despite the chaotic atrial activity, proving that the AV node is not conducting the atrial impulses to the ventricles 1, 2
• The regular ventricular rhythm in the setting of AF indicates a junctional or ventricular escape rhythm has taken over, as the AV node is completely blocking atrial impulses 2

This combination is frequently misdiagnosed because clinicians expect AF to have an irregularly irregular ventricular response—the regular ventricular rate is the critical clue that complete heart block has supervened 2.

Immediate Management Priorities

Exclude Reversible Causes First

Before proceeding to permanent pacing, you must systematically rule out treatable etiologies 2:

• Medication review: Immediately discontinue or hold all AV-nodal blocking agents (beta-blockers, calcium channel blockers, digoxin, amiodarone, dronedarone) that may have precipitated complete block in a patient with pre-existing AF 2
• Electrolyte correction: Check and aggressively correct potassium, magnesium, and calcium abnormalities, as hyperkalemia in particular can cause complete AV block 2
• Acute ischemia evaluation: Obtain troponin and consider urgent coronary angiography if acute MI is suspected, as inferior MI can cause transient complete heart block 2
• Drug toxicity screen: Assess for digoxin toxicity (check level), beta-blocker or calcium channel blocker overdose 2

Assess Hemodynamic Stability

• Symptomatic bradycardia (syncope, presyncope, dizziness, heart failure symptoms, confusion from cerebral hypoperfusion) mandates immediate temporary pacing followed by permanent pacemaker implantation 1
• Even asymptomatic patients with this rhythm require permanent pacing because complete AV block carries unpredictable risk of sudden cardiac death and the escape rhythm may fail at any time 1, 2

Definitive Treatment: Permanent Pacemaker Implantation

Permanent pacemaker implantation is the definitive treatment and should proceed urgently once reversible causes are excluded. 1, 2

Pacing Indications

According to the 2018 ACC/AHA/HRS bradycardia guidelines 1:

• Third-degree (complete) AV block is a Class I indication for permanent pacing regardless of symptoms, because the risk of sudden death is unacceptably high 1
• High-grade AV block (≥2 consecutive non-conducted P waves with evidence of some AV conduction) is also a Class I indication for pacing 1
• The presence of AF does not change this indication—the complete block of atrial impulses to the ventricles meets criteria for third-degree block 2

Pacemaker Mode Selection

• Dual-chamber (DDD) pacing is typically not beneficial in permanent AF, as there is no organized atrial activity to track 3
• Single-chamber ventricular (VVI or VVIR) pacing is appropriate for patients in permanent AF with complete AV block 1
• Rate-responsive pacing (VVIR) is preferred over fixed-rate (VVI) to allow heart rate increase with activity, improving quality of life 1

Risk Stratification in This Patient Population

This elderly patient with hypertension and diabetes has multiple risk factors that increase both the likelihood of this arrhythmia and its complications:

• Hypertension is the most robust predictor of AF development and progression to complete AV block, causing left ventricular hypertrophy, left atrial enlargement, and conduction system fibrosis 4, 3, 5
• Diabetes accelerates atherosclerotic disease affecting the AV nodal artery and causes autonomic neuropathy that may worsen conduction 4
• Advanced age increases the prevalence of degenerative conduction system disease (Lev's disease, Lenègre's disease) 3
• First-degree AV block in hypertensive patients carries a 2.77-fold increased risk of progression to advanced AV block over 9 years 4

Critical Pitfalls to Avoid

• Do not assume AF always presents with an irregularly irregular ventricular response—a regular ventricular rate in AF is pathognomonic for complete AV block and requires urgent intervention 2
• Do not use atropine as a diagnostic or therapeutic trial in suspected infranodal block, as it is ineffective below the AV node and may paradoxically worsen conduction 6
• Do not delay pacemaker implantation while attempting to restore sinus rhythm with cardioversion—the complete AV block will persist regardless of atrial rhythm and the patient remains at risk for sudden death 2
• Do not start rate-control medications (beta-blockers, calcium channel blockers, digoxin) in this setting, as the ventricular rate is already dangerously slow from complete block 2
• Do not discharge the patient without either temporary pacing or continuous telemetry monitoring until permanent pacemaker implantation, as the escape rhythm may fail unpredictably 1, 2

Additional Diagnostic Workup

While preparing for pacemaker implantation 7, 8:

• Transthoracic echocardiography: Assess left ventricular systolic function, left atrial size, valvular disease, and structural abnormalities that may have contributed to both AF and conduction disease 8
• Thyroid function tests: Hyperthyroidism can precipitate AF and worsen AV conduction, while hypothyroidism can cause bradycardia 7, 8
• Complete metabolic panel: Document baseline renal function before contrast exposure if coronary angiography is planned 8

Long-Term Considerations After Pacemaker Implantation

• Anticoagulation for stroke prevention must be addressed separately based on CHA₂DS₂-VASc score—this patient with hypertension, diabetes, and age ≥65 has a score ≥3 and requires oral anticoagulation unless contraindicated 1
• Ventricular pacing percentage should be monitored, as high-burden right ventricular pacing (>40%) may lead to pacing-induced cardiomyopathy over time 3
• Device interrogation at 3-month intervals initially to assess pacing thresholds, lead integrity, and battery longevity 3