Bradycardia & conduction disease
Structural disease behind the block (amyloid, sarcoid, ischaemia, abscess) and LVEF for choosing the device.
Echo approach, step by step
The ACC/AHA/HRS guideline recommends TTE in newly identified LBBB, Mobitz type II, high-grade or third-degree AV block, whether or not structural disease is apparent [205]. Echo finds the cause and supplies LVEF, which determines the type of device [39].
- LV functionLVEF. With reduced EF and an expected high burden of ventricular pacing, CRT or conduction-system pacing is preferred to RV pacing [39].
- InfiltrationThick walls with low tissue velocities (amyloid); basal septal thinning and aneurysms (sarcoid) [30].
- IschaemiaInferior wall motion abnormality (acute inferior MI with AV block) [138].
- Aortic valveCalcific AS extending into the conduction system; post-TAVI; aortic root abscess in IE [136].
- CongenitalCongenitally corrected transposition, AVSD [25].
- HypothyroidismPericardial effusion [201].
- LVEF
- Wall thickness and texture
- Regional wall motion
- Aortic valve and root
- Pericardial effusion
Causes & echo clues
| Cause | Echo clue | Next |
|---|---|---|
| Degenerative conduction disease | Normal or calcified annulus | Pacing [205] |
| Acute inferior MI | Inferior RWMA | Revascularisation; block often transient [138] |
| Cardiac amyloidosis | Thick walls, low s′ and e′ | Amyloid work-up [30] |
| Cardiac sarcoidosis | Basal septal thinning, regional dysfunction | CMR, PET [205] |
| Endocarditis with root abscess | Perivalvular thickening or cavity | TOE, surgery [136] |
| Hypothyroidism | Effusion, low output | TSH [201] |
| Drugs, hyperkalaemia | Normal | Stop drug; correct K [205] |
Clinical pathway to the diagnosis
- Unstable?Atropine, then pacing (transcutaneous or transvenous) or an isoprenaline or adrenaline infusion [198,205].
- Reversible causesDrugs (beta-blockers, calcium-channel blockers, digoxin), potassium, thyroid, ischaemia, Lyme, sleep apnoea [205].
- ECG and monitoringCorrelate symptoms with rhythm [205].
- EchoIn higher-grade block [205].
- CMR or PETSuspected infiltrative or inflammatory disease, especially under 60 [205].
- Device selectionPacemaker, CRT, or ICD if cardiomyopathy [38,39].
Clinical pearls & pitfalls
Practical tipAV block under the age of 60 without a clear cause → look for sarcoidosis. Survival and ICD decisions depend on it [205].
- Pacing-induced cardiomyopathy can develop after years of RV pacing. Repeat echo if HF develops [39].
- New AV block in aortic valve endocarditis = perivalvular extension until proved otherwise [136].
Red flags
- Syncope, hypotension or heart failure with bradycardia [205]
- Mobitz II, high-grade or complete AV block [205]
- Conduction block in endocarditis → aortic root abscess [136]
- Young patient with AV block → sarcoidosis, lamin A/C, Lyme [205]