Lyme disease, caused by the bacterium Borrelia burgdorferi, is transmitted through the bite of infected ticks. While it often begins with a skin rash or flu-like symptoms, the infection can disseminate throughout the body, affecting the joints, nervous system, and, in a small percentage of cases, the heart. This cardiac involvement is known as Lyme carditis. Lyme carditis is a severe complication that can rapidly progress, leading to a sudden disruption of the heart’s rhythm. Symptoms may manifest as fainting, dizziness, or shortness of breath, and in rare instances, sudden cardiac death. Prompt recognition and treatment are paramount.
Understanding Lyme Carditis
Lyme carditis occurs during the early disseminated phase of the infection, typically weeks to months after the initial tick bite. The condition is characterized by the Borrelia burgdorferi bacteria invading the heart tissue, which triggers an inflammatory response. This inflammation specifically targets the heart’s electrical conduction system, often presenting as myopericarditis.
The bacteria show a particular affinity for the atrioventricular (AV) node, which coordinates the electrical signal between the heart’s upper and lower chambers. The resulting inflammation disrupts the normal flow of electricity through the AV node, causing a delay or complete block in the transmission of the electrical impulse to the ventricles. This damage precipitates the characteristic electrical abnormalities seen in Lyme carditis.
Why Electrocardiograms Are Essential Screening Tools
The Electrocardiogram (ECG or EKG) is a non-invasive, quick, and cost-effective test that measures the electrical activity of the heart. It is a primary screening tool when a patient presents with symptoms suggesting cardiac involvement following possible Lyme exposure. The ECG provides a snapshot of the heart’s electrical rhythm and conduction pathways, precisely where Lyme carditis causes its most significant damage.
When a patient reports symptoms such as lightheadedness, palpitations, or fainting, a healthcare provider will immediately order an ECG. The test’s ability to quickly identify a conduction block is useful because the heart rhythm abnormalities caused by Lyme carditis can change rapidly, sometimes within hours or days. Detecting these changes early allows for immediate hospitalization and continuous monitoring, which is necessary for severe cases.
Specific Electrical Abnormalities Revealed by ECG
Lyme carditis findings on an ECG are typically specific to atrioventricular (AV) block. An AV block represents a delay or complete interruption of the electrical signal traveling from the atria to the ventricles. The most frequent abnormality is a prolonged PR interval, which measures the time it takes for the electrical impulse to travel from the atria through the AV node to the ventricles.
This delay constitutes a First-Degree AV block, defined by a PR interval greater than 200 milliseconds, and is the most common initial finding. As inflammation worsens, the block can progress to higher degrees. Second-Degree AV block involves some electrical impulses failing to reach the ventricles. This can be Mobitz Type I, where the PR interval progressively lengthens before a beat is dropped, or Mobitz Type II, where beats are dropped without prior warning.
A prolonged PR interval exceeding 300 milliseconds often indicates a high risk of progression to a more severe block. The most severe finding is a Third-Degree AV block, also known as complete heart block. Here, no electrical impulses from the atria reach the ventricles, causing the atria and ventricles to beat independently. The degree of AV block in Lyme carditis can fluctuate, meaning a patient can move between different stages on consecutive ECGs.
Treatment and Monitoring After Detection
Once the ECG identifies a significant conduction abnormality, such as a high-grade AV block, immediate medical intervention is required. Patients with second-degree or third-degree AV block, or a PR interval greater than 300 milliseconds, are typically hospitalized for continuous cardiac monitoring. The primary treatment for Lyme carditis is antibiotic therapy, which targets the underlying bacterial infection.
Intravenous (IV) antibiotics, such as ceftriaxone, are initiated for hospitalized patients with severe conduction defects. This treatment continues until the AV block resolves or the PR interval shortens significantly. In approximately 35% to 60% of patients, a temporary pacemaker may be necessary to maintain a stable heart rate until the antibiotics take effect.
Lyme carditis has an excellent prognosis due to the reversibility of the heart block with appropriate antibiotic treatment. Conduction abnormalities usually begin to resolve within one week of starting therapy, and permanent pacemaker implantation is rarely needed. Following stabilization, patients transition to oral antibiotics to complete a full course of treatment, typically lasting 14 to 21 days.