When Antibiotics Treat Heart Block

Dear Editor, A 28-year-old female, nurse practitioner by profession, with no significant past medical history was referred to the emergency room from her physician's office for an abnormal electrocardiogram (ECG) after feeling sick with extreme fatigue and body aches for 3 weeks. About 3 days prior to admission, she started to feel dizzy prompting a visit to her physician. Her pertinent physical finding was an erythematous rash on her right upper arm [Figure 1] and lower back, which she was unaware of. As she lived in an endemic area for Lyme disease, tick bite was verified and she recalled having one a few weeks ago. Figure 1 Erythema migrans, annular lesion with partial central clearing on the right upper arm of the patient Her ECG showed complete heart block [Figure 2a] with junctional escape rhythm at 70 beats per minute (bpm). Her complete blood count, comprehensive metabolic panel, thyroid stimulating hormone, and chest X-ray were all normal. With a strong suspicion for Lyme disease, intravenous ceftriaxone was started and an IgM level for Borrelia burgdorferi and confirmatory Western blot analysis were ordered to establish the diagnosis, which later, were positive. Temporary pacemaker placement was deferred as the patient was asymptomatic and the ventricular rate was normal. During the first 24 hours after starting antibiotics, patient's symptoms worsened transiently with increased body aches, malaise and sweating. These were treated symptomatically with ketorolac. Over the next few days, the degree of atrio-ventricular (AV) block lessened [Figure ​[Figure2b2b and ​andc].c]. Finally, her PR interval was less than 300 milliseconds after 4 days of antibiotics and she was discharged home on oral cefuroxime to complete a total duration of 28 days. A follow-up ECG, 4 weeks after discharge was completely normal. Figure 2a ECG on presentation with complete heart block. There is non-conducted sinus tachycardia (rate approximately 120 bpm) with a junctional escape rhythm (rate approximately 70 bpm) Figure 2b ECG during hospitalization showing 2:1 AV block (atrial rate approximately 100 bpm, ventricular rate approximately 50 bpm) Figure 2c ECG during hospitalization showing sinus rhythm with Wenkebach AV block and a markedly prolonged PR interval (approximately 356 milliseconds) Carditis has been reported in approximately 4-10% in surveillance studies of untreated adults with Lyme disease in the U.S.[1] Cardiac involvement occurs within a few weeks to few months after the onset of infection.[2] Its manifestations include AV nodal conduction disturbance (most common), myocarditis, pericarditis, atrial and ventricular tachycardias, cardiomyopathy, congestive heart failure and possibly degenerative cardiac valvular disease.[3,4] The diagnosis of Lyme carditis is established by the presence of consistent epidemiologic and clinical features in conjunction with positive results of Lyme serologic testing. A careful history should address residence in or travel to endemic areas and prior tick bites and a careful physical examination should look for erythema migrans lesion/s. All types of AV blocks may occur in Lyme disease and the degree of AV block may vary within periods of minutes.[5] Electrophysiological studies have typically determined conduction delay occurring above the bundle of His, often within the AV node, but sino-atrial node dysfunction, intra-atrial block, fascicular and bundle branch block have all been described. Conduction disturbances that have been associated with unfavorable prognosis in Lyme disease are – a) low (ventricular) escape rhythms with high-grade AV block, b) transient lack of any escape rhythm with brief asystole and c) fluctuating bundle branch block related to either transient His-Purkinje system involvement or infranodal AV block.[6] Lyme carditis is suggested to be caused by infiltration of cardiac tissue particularly prominent in perivascular areas and interstitial regions by spirochetes and/or inflammatory response with macrophages and lymphocytes.[7,8] According to guidelines from Infectious Diseases Society of America, patients who are symptomatic (syncope or dyspnea) or have second- or third-degree AV block or have markedly prolonged PR interval (>300 milliseconds) should be hospitalized, monitored with cardiac telemetry and treated with intravenous (iv) antibiotics.[9] Ceftriaxone is the drug of choice and alternatives include iv cefotaxime and penicillin G. Intravenous antibiotics are continued until high-grade AV block is resolved and the PR interval has become less than 300 milliseconds and then switched to oral therapy (doxycycline, amoxicillin and cefuroxime). As seen in our patient, about 15% of the patients develop a Jarisch-Herxheimer reaction manifesting as transient worsening of symptoms within 24 hours of starting antibiotics. Patients with severe or symptomatic AV block may require a temporary pacemaker. The prognosis of Lyme carditis is good and complete AV block typically resolves within 1 week of starting appropriate antibiotics and minor conduction disturbances typically resolve within 6 weeks.[1] Because of this therapeutic response, placement of a permanent pacemaker should be avoided even in cases of high-grade AV block related to suspected Lyme disease until response to antibiotics can be assessed.