Phase 4 paroxysmal AV block in a patient with scleroderma

Area of Science:

• Cardiology
• Electrophysiology
• Systemic Autoimmune Diseases

Background:

• Systemic scleroderma is a rare autoimmune disease affecting connective tissues.
• Cardiac involvement in scleroderma can manifest as conduction abnormalities.
• Syncope is a concerning symptom that warrants thorough cardiac evaluation.

Observation:

• A 72-year-old male with limited cutaneous systemic scleroderma presented with recurrent syncope.
• Continuous telemetry monitoring revealed frequent episodes of paroxysmal atrioventricular (AV) block.
• Asystolic periods during AV block lasted up to 7.5 seconds.

Findings:

• Rhythm strip analysis identified phase 4 intra-His bundle block as the mechanism.
• Critical P-P intervals were observed to trigger the atrioventricular block.
• A narrow window of junctional escape to subsequent P wave intervals was required to terminate the block.

Implications:

• This case underscores the potential for severe cardiac conduction disturbances in scleroderma.
• Understanding the specific electrophysiological mechanisms is crucial for appropriate management.
• Implantation of a dual-chamber pacemaker effectively resolved the syncope and prevented further life-threatening bradyarrhythmias.