Sinoatrial Node Dysfunction and Connective Tissue Diseases: What Clinicians Should Know

By Dr. Abdelwahab Arrazaghi, MD, FABIM, FRCPC

When we think about sinoatrial node dysfunction (SND)—commonly known as sick sinus syndrome—we often picture it as a condition of aging, driven by degenerative fibrosis of the heart’s natural pacemaker. But growing evidence suggests there’s more to the story. Patients with connective tissue diseases (CTDs), such as lupus, rheumatoid arthritis, or systemic sclerosis, may be at higher risk of developing SND due to the way these autoimmune conditions affect the heart.

In this article, we’ll explore the connection between CTDs and SND, highlight the mechanisms at play, and discuss how to approach diagnosis and management in this unique patient population.

Why CTDs Affect the Sinoatrial Node

The link between CTDs and SND isn’t straightforward—it’s multifactorial. Here are some of the main mechanisms at play:

Inflammation and Direct Tissue Damage

Autoimmune myocarditis can infiltrate the sinoatrial node and surrounding atrial tissue, causing cell injury and fibrosis. This process disrupts the node’s ability to generate reliable impulses. We see this in conditions like lupus or rheumatoid arthritis.

Fibrosis and Tissue Remodeling

Diseases such as systemic sclerosis gradually replace normal tissue with fibrotic scar. When this scarring involves the conduction system, it alters the very architecture of the SA node, impairing impulse generation.

Vascular Compromise

Because the sinoatrial node depends on small branches of the coronary arteries, vasculitis seen in CTDs can limit blood supply, creating chronic ischemia and bradyarrhythmias.

Autonomic Nervous System Involvement

Some CTDs, including Sjögren’s syndrome and lupus, are associated with autonomic neuropathy. This can affect the pacing rate and adaptability of the SA node.

Medication Effects

Many patients with CTDs require long-term treatment with medications like hydroxychloroquine or corticosteroids. Hydroxychloroquine, in particular, has been linked to conduction abnormalities due to its toxic effects on myocytes.

Ankylosing Spondylitis and Conduction Disturbances

Patients with ankylosing spondylitis often develop conduction abnormalities, including atrioventricular block and SND. Chronic inflammation, fibrosis around the conduction system, and even aortic root disease can contribute.

How It Presents in Practice

For clinicians, one of the challenges is that symptoms of SND can overlap with the fatigue and malaise already common in CTDs. Still, red flags to watch for include:

• Persistent or intermittent sinus bradycardia

• Syncope, presyncope, or severe fatigue from chronotropic incompetence

• Alternating slow and fast rhythms (tachy-brady syndrome)

Because these can be easily dismissed as part of the autoimmune disease itself, careful distinction is essential.

Tools for Diagnosis

A stepwise approach works best:

• ECG: Look for sinus pauses, arrest, or bradycardia.

• Holter monitoring: Captures intermittent SND and tachy-brady events.

• Echocardiography or cardiac MRI: Assess for myocarditis, fibrosis, or structural changes.

• Autoimmune screening: ANA, ENA, RF, anti-SSA/SSB, or HLA-B27 can point toward an underlying CTD.

• 
  

Management: Balancing Autoimmunity and Rhythm Control

Treat the Underlying CTD

Corticosteroids and immunosuppressants may help stabilize inflammation-driven conduction issues. Early treatment is key to prevent fibrosis.

Consider Device Therapy

For patients with symptomatic, irreversible SND, a permanent pacemaker is often the most reliable solution. Dual-chamber devices are preferred due to their protective effect against atrial fibrillation and AV block progression.

Review Medications

Look closely at drugs such as hydroxychloroquine, which may worsen conduction issues, and weigh risks versus benefits.

Monitor Closely

High-risk groups—especially those with systemic sclerosis or ankylosing spondylitis—benefit from regular ECGs and Holter monitoring. Any unexplained syncope should prompt urgent evaluation.

The Takeaway

Sinoatrial node dysfunction in the setting of connective tissue disease is an underrecognized but clinically important complication. Its causes range from inflammation and fibrosis to vascular compromise, autonomic dysfunction, and even the medications we use to control the autoimmune disease itself.

By maintaining a high index of suspicion, clinicians can catch SND early, distinguish it from overlapping autoimmune symptoms, and intervene with a combination of anti-inflammatory therapy, careful drug review, and pacing when necessary.

In short: when a patient with lupus, scleroderma, rheumatoid arthritis, or ankylosing spondylitis presents with unexplained syncope or fatigue, it’s worth asking—could this be the heart’s pacemaker crying out for help?