SafeR 4: switch for third-degree atrioventricular block
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At the beginning of the tracing, atrial pacing with intrinsic atrioventricular conduction; 2 consecutive blocked atrial complexes; the AVB III criterion is fulfilled (non-programmable parameter, 2 consecutive blocked atrial activities); switch to DDD mode (vertical line);
The diagnosis of complete atrioventricular block is defined by the complete interruption of atrioventricular conduction and is based on the presence of atrioventricular dissociation, the atria and ventricles being under the control of independent pacemakers, with the ventricular rate slower than the atrial rate. There is no relationship between P waves and QRS complexes, while the PR intervals are variable without repetitive sequence.
An escape rate in a patient with third-degree AV block is generally regular, with the electrocardiogram showing atrioventricular dissociation and the presence of regular ventricular bradycardia with monomorphic QRS complexes. At times, the escape can be unstable or absent, its activity slowing down or interrupting abruptly, which can cause the occurrence of serious symptoms of varying degrees depending on the duration of the pause, including leading to sudden death.
In the SafeR algorithm, the BAV III criterion is not programmable. This criterion is not based on the presence of atrioventricular dissociation (slower and dissociated ventricular rate compared to the atrial rhythm, with regular ventricular escape) but rather on the presence of consecutive blocked P waves. The pacemaker therefore switches to the DDD mode when 2 consecutive atrial activities (sensed outside the refractory period or paced) are blocked. The number of consecutive blocked atrial activities leading to a mode switch cannot be changed.
Interrogation of the device memory allows viewing in detail the number of mode switches and the distribution between switches according to AVB I, AVB II, AVB III or Pause criteria.
The diagnosis of complete AV block is defined by the complete interruption of atrioventricular conduction following a conduction block located at the AV node, the bundle of His or bundle branches. The lower the location of the atrioventricular block (distal conduction disorder), the greater the risk that the escape rhythm will be slow, weak and intermittent, which explains the increased risk of syncope or sudden death. When the SafeR mode is programmed, the pacemaker switches to DDD mode when 2 consecutive atrial activities are blocked: AVB III criterion.
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