A 63-year-old woman presented with fever, cough, and recurrent presyncope following a lower respiratory tract infection. Initial telemetry demonstrated intermittent complete atrioventricular block with ventricular premature complexes. Despite correction of electrolyte abnormalities and withdrawal of QT-prolonging medications (prescribed for cough), she developed repetitive episodes of polymorphic ventricular tachycardia triggered by R-on-T phenomena, requiring electrical cardioversion and suppression with overdrive pacing after magnesium and phenytoin proved ineffective. A nasopharyngeal bio fire panel identified Mycoplasma pneumoniae , prompting initiation of targeted antibiotic therapy along with propranolol. Cardiac magnetic resonance imaging demonstrated myocardial edema with biventricular dysfunction, consistent with acute myocarditis. With clinical stabilization, resolution of infection, and restoration of sinus rhythm following 2 weeks of antibiotic therapy, atrioventricular conduction improved; however, the QTc remained persistently prolonged on serial electrocardiograms. This persistent QT prolongation beyond the acute inflammatory phase prompted genetic testing, which revealed an autosomal dominant loss-of-function mutation in KCNH2, consistent with long QT syndrome type 2. Following further stabilization, a dual-chamber permanent pacemaker was implanted to prevent bradycardia-mediated arrhythmogenic triggers. The patient has remained free of recurrent ventricular arrhythmias at 1-year follow-up. In conclusion, this case illustrates a rare convergence of infectious, structural, and genetic substrates producing a potent arrhythmogenic milieu, in which Mycoplasma myocarditis unmasked an underlying severe long QT syndrome 2 (LQT2) phenotype and precipitated malignant polymorphic ventricular tachycardia.
Question 1
This patient was admitted with fever, cough, and recurrent presyncope. Telemetry showed intermittent complete heart block ( Figures 1 (Panel A), Figure 2 , and Figure 3 ). After placement of a temporary pacemaker, she develops sinus rhythm with a QTc of 600 milliseconds and prominent U waves ( Figure 4 ). A few hours later, she develops recurrent polymorphic ventricular tachycardia triggered by R-on-T premature ventricular complexes. ( Figure 1 (Panel B)) Electrolytes (hypokalemia and hypomagnesemia) have been corrected.
( A ) is a telemetry record showing intermittent complete heart block, ( B ) showing bradycardia followed by R on T phenomena inducing TdP and ( C ) showing termination of TdP using overdrive pacing. TdP = torsades de pointes.
Cardiac magnetic resonance imaging showing elevated T2 map value (75 milli-seconds) in mid and basal left ventricular myocardium.
Electrocardiogram showing resolution of AV block but persistence of QT prolongation after 2 weeks treatment of mycoplasma myocarditis.
Electrocardiogram taken half an hour after placement of a temporary pacemaker showing sinus rhythm with markedly prolonged QT interval of 600 milli-seconds along with prominent U wave.
Which of the following is the most appropriate next step to prevent further episodes?
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A.
Initiate lidocaine infusion.
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B.
Administer amiodarone bolus.
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C.
Increase the pacing rate of temporary pacemaker to 100 beats per minute.
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D.
Perform synchronized cardioversion.
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E.
Insert a permanent pacemaker immediately.
Question 2
Nasopharyngeal bio fire was positive for Mycoplasma pneumoniae in this patient. The team plans to treat the infection. Her QTc remains severely prolonged, and she has a homozygous autosomal dominant KCNH2 loss-of-function mutation.
Which antibiotic regimen is most appropriate?
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A.
Azithromycin.
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B.
Clarithromycin.
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C.
Erythromycin.
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D.
Doxycycline.
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E.
Levofloxacin.
Question 3
After 2 weeks of antibiotic therapy, atrio-ventricular (AV) conduction improves. However, her QTc remains prolonged due to congenital LQT2 ( Figure 3 ). She remains on high-dose propranolol for arrhythmia suppression. What should be the next most appropriate long-term device therapy?
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A.
Implant an implantable cardioverter-defibrillator (ICD) alone.
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B.
Implant a dual-chamber pacemaker.
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C.
No device needed because AV block resolved.
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D.
Implant a single-chamber pacemaker.
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E.
Implant a combined cardiac resynchronization therapy with defibrillator (CRT-D).
Question 4
Which of the following correctly describes how M. pneumoniae contributed to this patient’s arrhythmia presentation?
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A.
Direct inhibition of KCNQ1 channels, producing LQT1.
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B.
Immune-mediated myocarditis impairing AV nodal conduction.
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C.
Toxin-mediated catecholamine surge prolonging QT.
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D.
Directly infecting the Purkinje system and causing ventricular fibrillation.
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E.
Generation of autoantibodies that block sodium channels.
Question 5
After recovering from her infection, the patient’s AV block resolves and her electrolytes are normal. Despite this, the QTc remains markedly prolonged ( Figure 3 ). Which of the following best explains the persistence of her QT prolongation?
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A.
Residual myocarditis suppressing AV node conduction.
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B.
Excessive beta-blockade causing delayed repolarization.
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C.
Rapidly activating delayed rectifier potassium current (Ikr) dysfunction due to a KCNH2 loss-of-function mutation.
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D.
Chronic structural heart disease affecting conduction.
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E.
Ongoing magnesium deficiency.
Question 6:
In patients with complete heart block, the QT interval is often more prolonged than in patients with sinus bradycardia at similar heart rates. Which electrophysiologic mechanism best explains this phenomenon?
-
A.
Increased activation of the transient outward potassium current (Ito).
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B.
Enhanced inactivation of the IKr current at slower heart rates.
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C.
Depolarization of the resting membrane potential by the Na⁺/K⁺ pump.
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D.
Increased activation of L-type calcium channels at rapid rates.
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E.
Shortening of action potential due to escape rhythms.
Question 7:
After completing antibiotic therapy, AV conduction partially recovers, but QT prolongation persists due to congenital long QT syndrome ( Figure 3 ). The patient remains on propranolol. Which of the following best justifies choosing a dual-chamber pacemaker rather than an Implantable cardioverter-defibrillator?
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A.
Pacemakers shorten QT interval directly.
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B.
Beta-blockers are contraindicated in implantable cardioverter-defibrillator recipients.
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C.
The primary arrhythmogenic trigger was bradycardia.
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D.
ICDs are ineffective in treating torsades de pointes (TdP).
-
E.
Pacemakers prevent sudden cardiac death in LQT2.
Question 1: Correct response C . Increase the pacing rate of temporary pacemaker to 100 beats per minute.
Explanation: This patient has bradycardia-dependent TdP in the setting of complete heart block and congenital long QT syndrome 2 (LQT2). Overdrive pacing at 90 to 110 beats per minute is the most effective intervention to shorten the QT interval and suppress early after depolarizations. ,
Amiodarone may worsen QT interval; cardioversion terminates but does not prevent recurrence; permanent pacemaker implantation is deferred during active infection.
Question 2: Correct response D . Doxycycline.
Explanation: Macrolides (azithromycin, clarithromycin, erythromycin) and fluoroquinolones prolong QT by blocking IKr channels—a critical risk in LQT2.
Doxycycline is the correct choice because it is effective for Mycoplasma and does not worsen QT prolongation.
Question 3: Correct response B . Implant a dual-chamber pacemaker.
Explanation: Although this patient has congenital long QT syndrome type 2 (LQT2), and a QTc >500 milliseconds is itself a recognized high-risk marker for malignant ventricular arrhythmias, the dominant arrhythmogenic mechanism in this case was pause-dependent and bradycardia-mediated, occurring in the setting of myocarditis-related high-grade atrioventricular block rather than spontaneous ventricular arrhythmias at normal or elevated heart rates. ,,, The documented episodes of polymorphic ventricular tachycardia were precipitated by long pauses and R-on-T phenomena, consistent with pause-dependent TdP. ,,,,
In this context, the primary therapeutic priority was elimination of bradycardia and long pauses, which represent potent arrhythmogenic triggers in patients with long QT syndrome, particularly LQT2. ,, A dual-chamber permanent pacemaker directly addresses this mechanism by maintaining atrioventricular synchrony, preventing pause-dependent TdP, and enabling safe continuation and up-titration of high-dose β-blocker therapy. ,, Following pacing and resolution of the inflammatory trigger, the patient remained free of recurrent ventricular arrhythmias.
Importantly, although QTc prolongation necessitates ongoing risk stratification and close surveillance, , arrhythmic risk assessment in congenital long QT syndrome is inherently multifactorial and must be interpreted in aggregate with other clinical features, several of which are potentially reversible. In this patient, other major high-risk factors—including prior syncope, family history of sudden cardiac death, and recurrent ventricular arrhythmias after correction of bradycardia—were absent, and reversible contributors were effectively addressed. ,, The persistence of QTc prolongation after resolution of acute myocarditis therefore supported the interpretation that infection-related inflammation acted as a trigger unmasking an underlying channelopathy, rather than reflecting ongoing electrical instability. ,
Accordingly, following clinical stabilization and elimination of the bradycardia-related trigger, a mechanism-directed pacing strategy was selected as the most appropriate initial long-term device therapy. While economic considerations were discussed with the patient, clinical context, arrhythmia mechanism, and observed response to pacing were the primary determinants of management, with ICD implantation reserved for future consideration should the arrhythmic risk profile evolve over time. ,,
Question 4: Correct response B . Immune-mediated myocarditis impairing AV nodal conduction.
Explanation: M. pneumoniae is known to cause myocardial inflammation, resulting in transient AV block and bradycardia, which precipitated TdP in this patient with latent LQT2. Mycoplasma -induced myocarditis can transiently impair AV conduction thereby producing severe bradycardia and enhancing QT prolongation which promotes early after depolarizations and TdP. In a patient with LQT2, bradycardia is a potent arrhythmogenic trigger.
Question 5: Correct response C . IKr dysfunction due to a KCNH2 loss-of-function mutation.
Explanation: Her congenital LQT2 (KCNH2 mutation) results in reduced IKr current, leading to prolonged repolarization regardless of heart block resolution or electrolyte status. This persistent prolongation is why she required pacing support and beta-blockade.
Question 6: Correct response B . Enhanced inactivation of the IKr current at slower heart rates.
Explanation: Bradycardia prolongs repolarization, allowing increased inactivation of IKr, which is a major contributor to the action potential’s phase 3. This predisposes to early after depolarizations and TdP. Additionally, reduced Ito activation at slow rates shifts the plateau to more depolarized levels, promoting calcium window currents. ,,,
Question 7: Correct response C. The primary arrhythmogenic trigger was bradycardia.
Explanation: In this patient, recurrent episodes of TdP were clearly pause-dependent and bradycardia-mediated, occurring in the setting of myocarditis-related atrioventricular block rather than spontaneous ventricular arrhythmias at normal heart rates. ,,, Bradycardia and prolonged pauses are well-recognized arrhythmogenic triggers in congenital long QT syndrome, particularly LQT2, through facilitation of early afterdepolarizations; accordingly, elimination of bradycardia and long pauses represented the primary therapeutic priority. ,, A dual-chamber permanent pacemaker was therefore selected to maintain atrioventricular synchrony, prevent pause-dependent TdP, and permit safe continuation and up-titration of beta-blocker therapy, directly targeting the dominant arrhythmogenic mechanism. ,,
Although QTc prolongation itself represents an important high-risk marker, arrhythmic risk stratification in congenital long QT syndrome is inherently multifactorial and must be interpreted in aggregate with other clinical features, several of which are potentially reversible. , In this patient, other major high-risk factors—including prior syncope, family history of sudden cardiac death, and recurrent ventricular arrhythmias following correction of bradycardia—were absent, and reversible contributors were effectively addressed. ,, Importantly, the persistence of QTc prolongation after resolution of acute myocarditis supported the interpretation that infection-related inflammation acted as a trigger unmasking an underlying channelopathy, rather than reflecting ongoing electrical instability. , In this context, while implantable cardioverter-defibrillator therapy remains an important consideration in long QT syndrome, a mechanism-directed pacing strategy was selected as the most appropriate initial long-term device therapy, with defibrillator implantation reserved for future consideration should the arrhythmic risk profile evolve. ,,
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