Inflammatory Cardiac Disease in a Young Adult With Syncope

Scenario: A 32-year-old man arrived in the emergency department about 30 minutes after losing consciousness while watching television. He had experienced “racing heart,” dizziness, and breathlessness intermittently in the past 2 to 3 weeks, more intensely in the past week. The patient had gone hiking in the White Mountains in New Hampshire about 2 months earlier, where he developed a red rash on his left thigh. After returning from that trip, he developed a headache, muscle aches, and low-grade fever with chills, which he attributed to the flu. He did not seek medical attention and felt better a week after having taken an over-the-counter pain and fever medication. He had no history of joint pain or facial asymmetry or weakness. Vital signs on arrival: body temperature 36.5 ºC (97.6 ºF), pulse rate 40/min and regular, blood pressure 108/59 mm Hg. Cannon A waves were seen on the jugular venous pulse examination. No skin rash was noted. An initial electrocardiographic (ECG) rhythm strip in lead II provided by emergency medical services is shown below.Third-degree (complete) heart block with a junctional escape rhythm of 40 beats per minute.Normally, the electrical impulse generated by the sino atrial (SA) node in the right atrium spreads to both atria and reaches the atrioventricular (AV) node, where it is delayed, allowing adequate ventricular filling. The impulse is then routed through a specialized conducting system of intraventricular conduction pathways, which include a bundle of His, right and left bundle branches, and fibers of Purkinje cells. An AV block occurs when this impulse propagation is slowed or interrupted anywhere in this pathway.The severity of the AV block ranges from first degree (all impulses are conducted from atria to ventricles albeit with a delay) to second degree (some impulses are not conducted) to complete or third-degree block (no impulses are conducted). The AV node and His-Purkinje cells have intrinsic automaticity but are normally suppressed by the SA node owing to their higher firing rate. However, when the impulse from the SA node is blocked, a conduction disturbance occurs, allowing escape rhythms to emerge from the more distant pacemakers. A complete heart block is an example of an AV dissociation where the ventricular rate is slower than the atrial rate. As no impulse is conducted from the atria to the ventricles, the latter must be paced by escape rhythms at or below the AV node. An escape rhythm that arises from the AV node (junctional) usually generates a ventricular rate of 40/min to 60/min with a narrow QRS complex (seen in this case) as the impulse traverses the usual conduction pathway. Conversely, a block distal to the AV node generates a ventricular escape rhythm with slower rates of 20/min to 40/min and a wide QRS complex. The P-wave morphology appears different when it overlaps with the T wave. Given the irregular rhythm, there is a potential for a wandering atrial pacemaker, though confirmation would require additional leads and/or prolonged ECG recording to assess the atrial activity fully.Atrioventricular block can be caused by increased vagal tone and several pathologic conditions. Given that this young adult patient had no cardiac history and experienced a rash, headache, fever, and muscle aches shortly after traveling to a Lyme-endemic area and developing syncope, his acute symptoms are most likely due to Lyme disease. Lyme disease is a tick-borne infection most commonly caused by Borrelia burgdorferi. The symptoms of Lyme carditis, seen in 4% to 10% of all patients, are caused by transmural inflammation of the heart muscle, leading to AV conduction and other cardiac abnormalities.After ensuring the patient’s hemodynamic stability, the nurse should obtain a 12-lead ECG (given that only a single-lead ECG was initially available) to confirm the diagnosis and assess for other potential cardiac abnormalities. Pending serologic confirmation of Lyme disease, empirical treatment with intravenous antibiotics was initiated, and a cardiologist was consulted for the AV block. The severity of AV block in Lyme carditis can fluctuate rapidly in a short period. As this patient presented with syncope and complete heart block, a temporary pacemaker may be indicated. Close monitoring and continuous ECG are warranted.