Lightheadedness and palpitations for three days

Forestry worker. Spent August clearing scrub; treated an expanding red rash on the thigh himself with antiseptic cream about four weeks ago. No regular medication, no drugs, no family history of sudden death. Referred in by his GP after an ECG at the surgery.

Stage 1 of 2

He walks into the department and gives a clear history: three days of skipped beats and a swimming feeling when he stands up from a crouch, once nearly going down while loading a trailer. No chest pain, no syncope, no fever now. Chest is clear, heart sounds are normal, there is no murmur and no rub. The GP's ECG has been repeated at triage.

Tracing 1 of 2 for the quiz “Lightheadedness and palpitations for three days”. — 12-lead recorded at triage. Open this tracing in the studio

Observations

HR: 50
SpO₂ (%): 98
Respiratory rate: 14
Temperature (°C): 37.4
Systolic BP (mmHg): 112
Diastolic BP (mmHg): 68

What does this tracing show?

AComplete AV block with a narrow junctional escape at about 50/min Your answer
B2:1 AV block, with every second P wave failing to conduct Your answer
CSinus bradycardia at about 50/min with a PR interval of 380 ms, every P conducted Correct answer Your answer
DSinus bradycardia at about 50/min with a PR interval of 180 ms and normal conduction Your answer
ESecond-degree block, Mobitz I, with progressive PR lengthening and a dropped beat Your answer

Every P wave is followed by a QRS complex, so conduction is intact, but the PR interval is markedly prolonged at about 380 ms. The rate is about 50 per minute with a regular P-P interval, confirming sinus bradycardia with first-degree AV block. Complete AV block would show P waves dissociated from the QRS. In 2:1 block half the P waves would not be conducted, giving twice as many P waves as QRS complexes, which is not seen here. There is no progressive PR lengthening or dropped beat to suggest Mobitz I.

Given the PR interval measured on this tracing, what is the appropriate next step?

ADischarge with a cardiology clinic appointment in two weeks and a repeat ECG then Your answer
BGive atropine 500 micrograms intravenously and repeat the ECG in one hour Your answer
CRefer for a permanent dual-chamber pacemaker before he leaves the department Your answer
DAdmit to a monitored bed with continuous ECG telemetry and serial ECGs Correct answer Your answer
EStart bisoprolol 2.5 mg orally for the palpitations and review him in the morning Your answer

A PR interval of 380 ms in a young man with a history suggesting Lyme disease carries a real risk of progression to higher-degree block, which in Lyme carditis can happen within hours. Admission to a monitored bed with serial ECGs is the appropriate step so that deterioration is detected immediately. Discharge with outpatient follow-up risks an unwitnessed progression to complete block. Atropine is not indicated when the patient is haemodynamically stable. A permanent pacemaker is premature because Lyme-related AV block almost always resolves with antibiotics.

Stage 2 of 2

He is admitted overnight. Borrelia burgdorferi IgM and IgG come back positive and intravenous ceftriaxone is started. At the 07:00 round he says he felt very heavy-legged walking to the toilet; the nurse recorded a pulse of 38 and a blood pressure of 104/62. A fresh 12-lead is taken at the bedside.

Tracing 2 of 2 for the quiz “Lightheadedness and palpitations for three days”. — 12-lead recorded on the monitored bed the next morning. Open this tracing in the studio

Observations

HR: 38
SpO₂ (%): 98
Respiratory rate: 15
Temperature (°C): 37.2
Systolic BP (mmHg): 104
Diastolic BP (mmHg): 62

Bloods

Borrelia Ig G: positive
Borrelia Ig M: positive
Troponin T (ng/L): 18
Potassium (mmol/L): 4.2

What has changed on this tracing compared with the one taken at triage?

AThe sinus node has stopped and a junctional rhythm at about 38/min conducts back to the atria after each QRS Your answer
BP waves at about 80/min now bear no relation to a regular narrow escape at about 38/min Correct answer Your answer
CConduction is now 2:1 from an atrial rate of about 80/min, giving a ventricular rate of about 38/min Your answer
DConduction is now 3:2 with a constant PR interval and every third P wave dropped Your answer
EThe sinus rate has fallen to about 38/min and the PR interval has lengthened further, with every P still conducted Your answer

The second tracing shows P waves marching at about 80 per minute with a regular narrow-complex escape at about 38 per minute, and the P waves bear no fixed relationship to the QRS complexes. This is complete AV block with a junctional escape, a progression from the first-degree block seen on the triage ECG. In 2:1 block the PR interval of conducted beats would be constant, and the ventricular rate would be exactly half the atrial rate. The sinus node is clearly still firing at a normal rate, ruling out sinus node failure.

How should his conduction be managed from here?

AContinue intravenous ceftriaxone on a monitored bed with transvenous pacing immediately available Correct answer Your answer
BStart an isoprenaline infusion on the ward and repeat the ECG in the morning Your answer
CSwitch to oral doxycycline and discharge him once the ventricular rate is above 50/min Your answer
DImplant a permanent dual-chamber pacemaker during this admission Your answer

AV block in Lyme carditis is expected to resolve with appropriate antibiotic treatment, so the mainstay is continuing intravenous ceftriaxone on a monitored bed with temporary transvenous pacing immediately available in case the escape rate falls further or he becomes haemodynamically unstable. A permanent pacemaker is not indicated because the block is almost always reversible. Switching to oral doxycycline is appropriate for early Lyme disease without cardiac involvement but not for established carditis with complete AV block. An isoprenaline infusion on an unmonitored ward would be unsafe.

Diagnosis

Lyme carditis causing AV block

Lyme carditis most commonly presents as AV block, and the block can fluctuate rapidly from first degree to complete within hours. The PR interval of 380 ms on the first tracing was already markedly prolonged, and by the following morning the conduction had failed entirely. This rapid progression is characteristic and is the reason admission to a monitored bed is the right response to a long PR in this context, even when the patient looks well.

AV block in Lyme disease nearly always resolves completely with antibiotic treatment, so a permanent pacemaker is not indicated during the acute illness. Temporary pacing may be needed if the escape rate falls further or haemodynamic compromise develops.

References

Steere AC, Batsford WP, Weinberg M, et al. Lyme carditis: cardiac abnormalities of Lyme disease. Ann Intern Med. 1980;93(1):8-16.
Forrester JD, Mead P. Third-degree heart block associated with Lyme carditis: a review of published cases. Clin Infect Dis. 2014;59(7):996-1000.

Lightheadedness and palpitations for three days

The case

On arrival

Observations

Observations

Bloods

Diagnosis

References

Discussion