Syncope with bifascicular block after myocardial infarction — case discussion

Presentation

Practice case (not a real patient). A 74-year-old man with an ST-elevation myocardial infarction (STEMI) 6 years ago lost consciousness without warning while sitting reading in an armchair, and recovered fully within a minute. His wife saw no jerking. He has had no chest pain or palpitations. Blood pressure (BP) is 136/80 mmHg supine and 132/78 mmHg after 3 minutes standing, without symptoms. Echocardiography later shows a left ventricular ejection fraction of 60%. The electrocardiogram (ECG) shows sinus rhythm at 68 beats per minute with right bundle branch block and left anterior fascicular block.^[1][5]

Step 1 — Is this syncope, and is it explained?

Discussion:

• European Society of Cardiology (ESC) 2018 defines syncope as transient loss of consciousness due to cerebral hypoperfusion with rapid onset, short duration and spontaneous complete recovery, and his event fits that pattern.^[1]
• His systolic BP fell by 4 mmHg and his diastolic BP by 2 mmHg, and systolic BP stayed above 90 mmHg, so active standing does not meet the ESC 2018 definition of an abnormal BP fall (a progressive and sustained fall in systolic BP from baseline value ≥20 mmHg or diastolic BP ≥10 mmHg, or a decrease in systolic BP to <90 mmHg) and does not show orthostatic hypotension (OH).^[1]
• Neither the ESC 2018 Class I criterion for vasovagal syncope (VVS) nor its arrhythmic ECG criterion is met: there is no trigger or typical prodrome for VVS, and his ECG shows none of the arrhythmic findings that make arrhythmic syncope highly probable.^[1]
• ESC 2018 Table 5 lists bifascicular block (left or right bundle branch block [BBB] combined with left anterior or left posterior fascicular block) among ECG findings suggesting arrhythmic syncope.^[1]
• American College of Cardiology/American Heart Association/Heart Rhythm Society (ACC/AHA/HRS) 2017 Table 4 lists older age (>60 years), male sex, known ischaemic heart disease and sudden loss of consciousness without prodrome as characteristics more often associated with cardiac causes of syncope.^[2]

Step 2 — Risk and disposition

Discussion:

• ESC 2018 Table 6 major high-risk features present: previous myocardial infarction (severe structural or coronary artery disease) and bundle branch block on the ECG.^[1]
• ESC 2018 Table 6 minor features present, which count as high-risk because he has structural heart disease and an abnormal ECG: no warning symptoms and syncope in the sitting position.^[1]
• ESC 2018 recommends early intensive and prompt evaluation in a syncope unit or an emergency department (ED) observation unit (if available), or hospitalisation, for patients with high-risk features (Class I, Level B).^[1]
• ESC 2018 indicates immediate in-hospital monitoring, in bed or by telemetry, in high-risk patients (Class I, Level C).^[1]
• ACC/AHA/HRS 2017 calls continuous ECG monitoring useful for hospitalised patients admitted for syncope evaluation with suspected cardiac etiology (class of recommendation [COR] I, level of evidence [LOE] B-NR).^[2]

Step 3 — Electrophysiological study

Discussion:

• Telemetry and echocardiography do not explain the event. ESC 2022 indicates programmed electrical stimulation (PES) in patients with syncope and previous STEMI when syncope remains unexplained after non-invasive evaluation (Class I, Level C).^[5]
• ESC 2021 also says an electrophysiology study (EPS) should be considered in syncope with bifascicular block when syncope remains unexplained after non-invasive evaluation or when an immediate decision about pacing is needed due to severity, unless empirical pacemaker implantation is preferred (especially in elderly and frail patients) (Class IIa, Level B).^[4]
• The EPS, including PES, shows a baseline His ventricular (HV) interval of 78 ms and no inducible ventricular tachycardia.

Step 4 — Treatment

Discussion:

• ESC 2021 indicates a pacemaker in unexplained syncope with bifascicular block when the baseline HV interval is ≥70 ms (Class I, Level B); his 78 ms meets this.^[4]
• In the ESC guidelines checked for this topic, the implantable cardioverter defibrillator (ICD) rows for this setting do not fit him; among them, the ESC 2022 rows for coronary artery disease need a left ventricular ejection fraction (LVEF) ≤40% despite ≥3 months of optimal medical treatment, non-sustained ventricular tachycardia and sustained monomorphic ventricular tachycardia inducible at PES (Class IIa, Level B), or New York Heart Association (NYHA) class I and an LVEF ≤30% despite ≥3 months of optimal medical treatment (Class IIa, Level B), and the ESC 2026 heart failure primary-prevention ICD rows need symptomatic heart failure with reduced ejection fraction (NYHA class II/III) and an LVEF ≤35% despite ≥3 months of optimal foundational medical therapy, in patients expected to survive longer than 1 year with good functional status; his LVEF is 60% and no ventricular tachycardia was induced.^[5][6] For a patient like him, more than 40 days after myocardial infarction, outside those ESC 2022 and ESC 2026 rows and without another disease that has its own ESC table, no newer ESC row was found on an ICD for syncope after myocardial infarction with ventricular tachycardia induced at EPS.^[1][5][6] The newest is therefore the ESC 2018 row: an ICD is indicated in patients with syncope and previous myocardial infarction who have ventricular tachycardia induced during EPS (Class I, Level C); none was induced in him.^[1]
• The ESC 2022 Class I, Level A secondary-prevention ICD rows (Recommendation Tables 12 and 24) need documented ventricular fibrillation or haemodynamically not-tolerated ventricular tachycardia; its chronic coronary artery disease row for haemodynamically tolerated sustained monomorphic ventricular tachycardia with LVEF ≥40% (Class IIa, Level C), which applies if ablation of that tachycardia fails, is not available or is not desired, needs the tachycardia documented; none has been documented in him.^[5]
• ESC 2018 states that, even if the quality of evidence is moderate, there is strong consensus that in bifascicular BBB with a positive EPS, cardiac pacing is highly effective in preventing syncope recurrence.^[1]

Step 5 — Driving and follow-up

Discussion:

• ESC 2021 states that, in syncope with bifascicular block, an HV interval ≥70 ms identifies a group at higher risk of developing atrioventricular block (AVB).^[4]
• ESC 2018 states that less than half of patients with bifascicular BBB and syncope have a final diagnosis of AV block, and a similar percentage have a final diagnosis of reflex syncope.^[1]
• ESC 2018 states that an HV interval ≥70 ms identifies a group at higher risk of developing AV block, and that there is strong consensus that a positive EPS indicates that the likely mechanism of syncope is paroxysmal AV block; his HV interval was 78 ms.^[1]
• On that reading, the pacemaker rows for driving apply: ACC/AHA/HRS 2017 Table 10 suggests 1 week before private driving after syncope due to nonreflex bradycardia treated with a permanent pacemaker.^[2]
• ESC Web Table 3 (cardiac arrhythmias) allows group 1 (private) drivers to drive 1 week after a pacemaker implant, and group 2 (professional) drivers after appropriate function is established (first post-implant visit).^[3]
• If the cause is instead judged undetermined, ACC/AHA/HRS 2017 Table 10 suggests 1 month for syncope of undetermined etiology, and, for a group 1 (private) driver, ESC Web Table 3 defers driving for unexplained syncope without prodrome until diagnosis and appropriate therapy are established.^[2][3]
• ACC/AHA/HRS 2017 states that it can be beneficial for clinicians to know the driving laws and restrictions in their regions and to discuss the implications with the patient (COR IIa, LOE C-EO).^[2]