Atrial lead impedance
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This transmission shows a “Atrial lead impedance” alert, which is triggered when the atrial lead impedance is below 200 Ohms or above 2000 Ohms. The last atrial impedance was 2403 Oms. While a completely severed lead would result in an impedance of >3000 Ohms, the value of 2403 Ohms is also clearly outside of the normal range (<1000 Ohms). When looking at the trends, the high impedance has been around this value and stable for a few months prior. While sensing shows good values (5.6 mV), the atrial pacing threshold is very high (3V at 0.35ms). Within the transmission, there are two Mode Switch episodes which show intermittent oversensing on the atrial channel. The oversensed signals are chaotic, large amplitude and non-physiologic in nature. Together with the increased impedance and high pacing threshold, the lead noise confirms the diagnosis of atrial lead dysfunction is confirmed.
In patients with signs of atrial lead dysfunction, the diagnosis is often difficult as the lead still functions nearly all of the time and does not cause any symptoms. The risks of a dysfonctioning atrial lead is obviously a lot less than a dysfonctioning ventricular lead which is associated with multiple inappropriate therapies and syncope due to loss of ventricular capture. In ICDs, the atrial lead is often used for atrial pacing in patients with slow sinus rates or chronotropic dysfunction, often aggravated by medical treatment in the context of their cardiomyopathy. This is also the case in the patient of this case, who is paced in the atrium 84% of the time, mostly sensor-driven in Safer-R mode. Importantly, in ICD patients, proper functioning of the atrial lead is also important as it is part of the discrimination algorithm which differentiates between supraventricular and ventricular arrhythmies. In case of atrial lead dysfunction, tachycardias may be wrongly classified as ventricular or supraventricular. It is recommended to reprogram the discrimnation algorithm (de-activate PARAD+) in case of suspected atrial lead dysfunction. The patient should be seen in-clinic to confirm the diagnosis (noise exacerbation maneuvres and X-ray), perform programming changes and discuss intervention. In this case it was decided to add a new atrial lead and abandon the existing atrial lead (which is 18 years old).
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