Lyme disease is the most common tick-borne illness in the United States, transmitted by the bite of an infected Ixodes tick. The infection is caused by the bacterium Borrelia burgdorferi, a spiral-shaped organism known as a spirochete. While known for causing a characteristic skin rash, joint pain, or neurological issues, the infection can also reach the heart. When heart tissue becomes inflamed due to this infection, the condition is termed Lyme carditis, which typically occurs during the early disseminated phase of the disease.
The Mechanism of Cardiac Invasion
The development of Lyme carditis begins when Borrelia burgdorferi spirochetes disseminate from the initial bite site into the bloodstream. These bacteria show a preference for the heart tissue, where they infiltrate the muscle and the specialized electrical conduction system. Spirochetes are often concentrated in the atrioventricular (AV) node, a small region that acts as the primary electrical gatekeeper between the heart’s upper and lower chambers.
Damage to the heart is caused primarily by the resulting severe inflammatory response, not solely by the physical presence of the spirochetes. The immune system recognizes the invading bacteria and launches an attack, leading to myocarditis, or inflammation of the heart muscle. Immune cells, such as macrophages and lymphocytes, accumulate around the AV node, causing swelling and disruption of the normal cellular structure.
This intense, localized inflammation directly interferes with the heart’s electrical wiring. The severity of the conduction abnormality correlates with the degree of inflammation and the number of spirochetes present. In some instances, the immune reaction may also involve cross-reactive antibodies that mistakenly target heart tissue components, further contributing to functional disturbances.
Identifying the Specific Symptoms
The most frequent and serious manifestation of Lyme carditis is a disturbance in the heart’s rhythm, known as Atrioventricular (AV) block. This condition occurs because inflammation in the AV node prevents electrical signals from traveling correctly from the atria to the ventricles. The blockage can progress rapidly and fluctuate, sometimes moving from a mild first-degree block to a complete heart block within hours or days.
A complete, or third-degree, heart block is a medical emergency where the electrical connection between the upper and lower chambers is entirely severed. This severe disruption causes a sudden drop in heart rate, leading to symptoms because the brain and body do not receive enough blood. Patients may experience sudden fainting, known as syncope, or near-fainting episodes characterized by dizziness and lightheadedness.
Other common symptoms include breathlessness, or dyspnea, as the inefficient heart struggles to circulate oxygenated blood effectively. Patients may also feel palpitations, which are sensations of a rapid, fluttering, or pounding heart, reflecting the disorganized electrical activity. Lyme carditis typically presents in the early disseminated stage of the infection, often appearing a few weeks to a few months after the initial tick exposure.
Diagnosis, Treatment, and Expected Recovery
Diagnosis requires combining a patient’s clinical presentation with specific laboratory and cardiac tests. Physicians look for symptoms like syncope or unexplained dizziness, especially in a young person with recent exposure in an endemic area. The definitive cardiac test is the electrocardiogram (ECG), which confirms the presence and degree of the AV block.
Blood tests are simultaneously performed to check for antibodies against Borrelia burgdorferi, confirming the infection. Because the conduction block can fluctuate rapidly, continuous cardiac monitoring is necessary once Lyme carditis is suspected. High-degree AV block necessitates hospitalization for close observation and immediate treatment.
The primary treatment for Lyme carditis is the administration of intravenous antibiotics, such as ceftriaxone, to eliminate the bacterial infection. For patients experiencing a high-grade heart block or hemodynamic instability, a temporary cardiac pacing wire is an immediate, life-saving measure. This temporary pacemaker supports the heart rate until the inflammation subsides and the natural conduction system recovers.
The prognosis for Lyme carditis is favorable when treated promptly. Unlike some other forms of severe heart damage, the inflammation is usually temporary and completely reversible. Most patients see a full resolution of the heart block within approximately one week of starting antibiotic therapy, making the implantation of a permanent pacemaker rarely necessary.