Description:
<jats:title>Abstract</jats:title>
<jats:p>An 80-year-old woman received a dual chamber pacemaker (Boston Scientific Accolade MRI DR) for pre-syncopal episodes associated with transient type 1 and 2:1 II degree atrioventricular block, recorded in 24-hour Holter monitoring. Due to residual AV conduction, pacemaker was set with RYTHMIQ algorithm, in order to reduce inappropriate ventricular pacing. A month later, the patient began to complain of severe asthenia and bradycardia (46-48 bpm). Telemetry-supported pacemaker control revealed III degree AV block with junctional escape rhythm, unmasking failing to switch of RYTHMIQ algorithm.</jats:p>
<jats:p>Why did it happen?</jats:p>
<jats:p>The RythmIQ algorithm has been designed to promote intrinsic conduction in Boston Scientific devices. With RythmIQ the device provides AAI(R)[i] at the lower rate limit and/or sensor indicated rate. It provides backup VVI pacing at a rate 15 bpm slower than the programmed lower rate limit, with backup VVI pacing rate limited to no slower than 30 bpm and no faster than 60 bpm. If 3 slow ventricular beats are detected in a window of 11 beats, the device automatically switches to DDD(R) mode. A slow beat is defined as a ventricular paced or ventricular sensed event that is at least 150 ms slower than the AAI(R) pacing rate. Slow ventricular beats are any of the following: - V paced event- V sensed event &gt; AAI lower rate limit + 150 ms- V sensed event &gt; AAI(R) sensor indicated rate + 150 ms</jats:p>
<jats:p>In our case LRL was set at 50 bpm (1200 ms). During III degree AV block, patient's ventricular rate was always about 46-48 bpm, due to stable junctional escape rhythm. Thus no ventricular sensed event occurred with a V-V cycle greater than AAI lower rate limit + 150 ms, namely 1350 ms (around 44 bpm). Moreover the device didn't provide backup VVI pacing at a rate 15 bpm slower, namely 35 bpm. This two conditions impaired Rhythm IQ switching from AAI with VVI backup to DDD.</jats:p>
<jats:p>The device was set manually in DDD with restoring of AV synchrony and adequate ventricular rate followed by complete resolution of symptoms.</jats:p>
<jats:p>Rhythm-IQ algorithm doesn't check for AV synchrony, providing switch from AAI with VVI backup to DDD just in case of sudden and marked bradycardia. Loss of AV synchrony doesn't represent a switching criteria and moreover it is not recognized by the device. This condition could be dangerous failing to correct AV conduction disturbances in pacemaker recipient, especially if LRL was set ≤ 50 bpm. For this reason, adequate knowledge of the algorithm would indicate greater caution in using RythmIQ in certain categories of patients, such as the one in the case just described.</jats:p>