ECG rhythm recognition and conduction blocks — structured written assessment

SAQ 1 (10 marks)

Practice scenario. A 78-year-old man has had two episodes of unexplained syncope. His ECG in sinus rhythm shows a QRS of 150 ms with broad notched R waves in I, aVL, V5 and V6 and no q waves in I, V5 or V6; an ECG three years ago was normal. Non-invasive evaluation has not explained the syncope.^[3]

1. How do ESC 2021 and the 2009 AHA/ACCF/HRS statement each treat the term bifascicular block? (2)^[1][3]
2. List four of the 2009 criteria for complete LBBB in adults. (2)^[3]
3. What imaging does ACC/AHA 2018 recommend for newly detected LBBB, with class and level, and why? (2)^[2]
4. What EPS findings lead to a pacemaker under ESC 2021 and under ACC/AHA 2018, with class and level? (2)^[1][2]
5. If his EPS is negative, what does ESC 2021 say about the result and further evaluation, and what option does it give for selected patients without EPS? (2)^[1]

Model answers — SAQ 1

1. ESC 2021 defines bifascicular block as LBBB, or RBBB combined with left anterior or posterior fascicular block, so his LBBB counts as bifascicular block in ESC terms (1 mark).^[1] The 2009 statement does not recommend the term bifascicular block, because of the great variation in anatomy and pathology producing such patterns, and asks for each defect to be described by the structures involved (1 mark).^[3]
2. Any four: QRS 120 ms or more; broad notched or slurred R wave in I, aVL, V5 and V6; absent q waves in I, V5 and V6 (a narrow q wave may be present in aVL in the absence of myocardial pathology); R peak time above 60 ms in V5 and V6 but normal in V1 to V3 when small initial r waves can be discerned; ST and T waves usually opposite in direction to QRS (half a mark each).^[3]
3. ACC/AHA 2018: with newly detected LBBB, a transthoracic echocardiogram to exclude structural heart disease is recommended (COR I, LOE B-NR) (1 mark).^[2] ACC/AHA 2018 says LBBB on the ECG markedly increases the likelihood that left ventricular systolic dysfunction will be diagnosed by echocardiogram (1 mark).^[2]
4. ESC 2021: in unexplained syncope with bifascicular block, a pacemaker is indicated with a baseline HV of 70 ms or more, second- or third-degree intra- or infra-Hisian block during incremental atrial pacing, or an abnormal response to pharmacological challenge (Class I, Level B) (1 mark).^[1] ACC/AHA 2018: in syncope with bundle branch block and an HV interval of 70 ms or greater or evidence of infranodal block at EPS, permanent pacing is recommended (COR I, LOE C-LD) (1 mark).^[2]
5. ESC 2021: in unexplained syncope with bifascicular block, a negative EPS cannot rule out intermittent or paroxysmal AV block as the cause of syncope; in such patients with a negative EPS, intermittent or stable AV block was documented by implantable loop recorder in about 50% of cases (half a mark).^[1] ESC 2021: a negative EPS does not exclude an arrhythmic syncope, and further evaluation is warranted; in infrequent (less than once a month) unexplained syncope or other symptoms suspected to be caused by bradycardia, in whom a comprehensive evaluation did not demonstrate a cause, long-term ambulatory monitoring with an implantable loop recorder is recommended (Class I, Level A) (half a mark).^[1] ESC 2021: pacing may be considered in selected patients with unexplained syncope and bifascicular block without EPS (elderly, frail, high-risk and/or recurrent syncope) (Class IIb, Level B) (1 mark).^[1]

SAQ 2 (10 marks)

Practice scenario. A 63-year-old woman presents with palpitations. Her ECG shows a regular tachycardia at 140 beats per minute with a QRS duration of 150 ms. She is alert, her blood pressure is maintained and she has no chest pain or signs of heart failure. No previous ECG is available.^[4][9]

1. What are the reported proportions of causes of wide QRS tachycardia, and what default diagnosis does ESC 2019 set? (2)^[4]
2. Give four ECG features from ESC 2019 Table 9 that suggest VT rather than SVT. (2)^[4]
3. How accurate are ECG-based methods, according to ESC 2019? (2)^[4]
4. Compare the ESC 2019 and ESC 2022 rows on adenosine and on verapamil. (2)^[4][5]
5. State the two ANZCOR summary recommendations on wide-QRS tachycardia of uncertain origin, with their ANZCOR classes. (2)^[9]

Model answers — SAQ 2

1. ESC 2019: wide QRS tachycardias can be VT, SVT with BBB aberration or antegrade conduction over an accessory pathway, with reported proportions of 80, 15 and 5% (1 mark).^[4] ESC 2019: the default diagnosis should be VT until proven otherwise, because misdiagnosis and drugs usually used for SVT can be harmful in VT (1 mark).^[4]
2. Any four: AV dissociation (ventricular rate above atrial rate); fusion or capture beats; negative chest lead concordance; absence of RS in the precordial leads or RS above 100 ms in any lead; QRS axis −90° to ±180°; R wave peak time in lead II of 50 ms or more; an initial R wave, initial R or Q above 40 ms, or a notch in a predominantly negative complex in aVR; RBBB or LBBB morphology criteria in V1 and V6 (half a mark each).^[4]
3. ESC 2019: independent studies found specificities of 40–80% and accuracies of about 75%, a figure that would be matched by calling every wide QRS tachycardia VT, because only 25–30% are SVTs (1 mark).^[4] The morphology criteria are not fulfilled in any lead in 4% of SVTs and 6% of VTs, and in one-third of cases V1 and V6 favour opposite diagnoses (1 mark).^[4]
4. Adenosine: ESC 2019, in haemodynamically stable wide QRS tachycardia without an established diagnosis, says adenosine should be considered if vagal manoeuvres fail and there is no pre-excitation on a resting ECG (Class IIa, Level C); ESC 2022 says adenosine or vagal manoeuvres should be considered in a regular, haemodynamically tolerated wide QRS tachycardia suspected for SVT (Class IIa, Level C) (1 mark).^[4][5] Verapamil: ESC 2019, among its rows for haemodynamically stable patients, says verapamil is not recommended in wide QRS tachycardia of unknown aetiology (Class III, Level B); ESC 2022 says i.v. verapamil is not recommended in broad QRS tachycardia of unknown mechanism (Class III, Level B) (1 mark).^[4][5]
5. ANZCOR Class A: wide-QRS tachycardia should be presumed to be VT if the diagnosis is unclear (Level of Evidence C) (1 mark).^[9] ANZCOR Class B: calcium channel blockers such as verapamil and diltiazem should not be used to terminate wide-QRS tachycardia of unknown origin, especially with a history of myocardial dysfunction (Level of Evidence IV) (1 mark).^[9]