From the Research
In complete heart block, there is no fixed S1 split, as the atrioventricular dissociation leads to irregular timing between atrial and ventricular contractions, causing variable and inconsistent valve closure timing. Complete heart block (also called third-degree AV block) occurs when the electrical impulses from the atria cannot reach the ventricles, causing the atria and ventricles to beat independently of each other. This means that the timing relationship between atrial and ventricular contractions is completely disrupted. Since S1 is produced by the closure of the mitral and tricuspid valves during ventricular contraction, and these valves normally close almost simultaneously, any splitting of S1 would be variable and inconsistent in complete heart block. The atrioventricular dissociation in complete heart block leads to irregular timing between atrial and ventricular contractions, which can cause varying hemodynamic conditions that affect valve closure timing. This is different from conditions like right bundle branch block, where a fixed splitting of S2 (not S1) can occur due to delayed right ventricular contraction.
Some key points to consider in complete heart block include:
- The lack of a fixed S1 split is a characteristic feature of complete heart block, as noted in various studies 1, 2.
- The atrioventricular dissociation in complete heart block can lead to varying hemodynamic conditions, which can affect valve closure timing and overall cardiac function 3, 4.
- Complete heart block is a serious condition that can be fatal if not urgently treated, and permanent pacemaker implantation is often the standard of care 1, 5.
In terms of management, the most recent and highest quality study suggests that permanent pacemaker implantation is the standard of care in patients with complete heart block and second-degree type II atrioventricular block, irrespective of patient symptoms 1. This is because complete heart block can be a medical emergency that can be fatal if not urgently treated. However, the decision to implant a pacemaker should be made on a case-by-case basis, taking into account the individual patient's needs and circumstances 1, 3.