Pain free and in VT?

The ECG shows sinus rhythm with rate-dependent left bundle-branch block.

The first eight QRS complexes show:

• Sinus rhythm at around 82 bpm
• Normal PR interval (160ms)
• Broad complexes (120ms)
• Typical LBBB morphology (leftward axis, deep S-wave in V1, broad ‘M’ pattern in I, aVL)

The remainder of the ECG shows:

• Slowing of the sinus rate to 60bpm
• Narrowing of the QRS complexes to 80ms
• Disappearance of the LBBB pattern

The appearance in the chest leads is suggestive of Wellens syndrome, with:

• Deep T wave inversions in the right- and mid-precordial leads (V1-4)
• Biphasic T wave morphology  in V2

There is also subtle T wave flattening and ST depression in the last four complexes of the lead II rhythm strip, indicating possible inferior ischaemia.

Rate-dependent bundle-branch block (AKA “tachycardia-dependent BBB”) is simple to understand:

• One of the bundle branches becomes diseased and rather than fail completely (which would produce a fixed bundle branch block pattern), it develops a prolonged refractory period.
• Below a certain rate, this prolonged refractory period has no effect; impulses are conducted normally.
• Above the ‘critical’ rate, the diseased bundle branch is unable to conduct impulses fast enough and a bundle branch pattern appears on the ECG.
• Rate related fascicular blocks (LAFB, LPFB) may also occur, producing left or right axis deviation respectively when the rate increases above a certain threshold.

Bradycardia-dependent bundle branch block (which is much less common) is essentially the opposite:

• A bundle branch pattern appears whenever the rate falls below a certain rate.
• This happens because of a tendency for damaged cells within the bundle branches to leak their charge and become inexcitable when the intervals between impulses are too long.

No specific treatment is required for rate-dependent LBBB.

In a patient presenting with recent chest pain, an ECG showing biphasic or deeply inverted T waves in leads V1-4 is highly specific for a critical occlusion of the proximal LAD – Wellens Syndrome

These patients may be pain free by the time the ECG is taken and have normally or minimally elevated cardiac enzymes; however, they are at extremely high risk for extensive anterior wall MI within the next 2-3 weeks.

There are two types of T wave inversions seen in Wellens syndrome.

Type A T-waves are biphasic:

Type B T-waves are deeply, symmetrically inverted:

• This patient needs urgent cardiology referral, admission to a monitored bed and early PCI (ideally within 48 hours).
• Medical management (including thrombolysis) is frequently ineffective in this condition.
• The only way to prevent progression to extensive anterior MI is revascularization via PCI or CABG.

• de Zwaan C, Bär FW, Wellens HJ. Characteristic electrocardiographic pattern indicating a critical stenosis high in left anterior descending coronary artery in patients admitted because of impending myocardial infarction. Am Heart J. 1982 Apr;103(4 Pt 2):730-6. PMID: 6121481
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