Optimization of device placement

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Tracing N° 1
Medtronic Devices: ILR
Patient

A 64-year-woman with a history of inferior myocardial infarction and 58% LVEF presented after 3 sudden episodes of syncope without apparent cause. A 12-lead ECG showed sinus rhythm, incomplete right bundle branch block and signs of old inferior myocardial infarction. The remainder of the diagnostic investigations, including electrophysiologic studies and programmed ventricular stimulation was negative. The device placement was optimized with Vector Check immediately before its implant.

Description:

The 4 tracings were recorded at the same sensing level and amplification. The device was implanted at the level of the 4th intercostal space in a horizontal axis on the 1st tracing, becoming progressively more vertical in the other 4 tracings. The ventricular electrograms are accurately sensed (VS) by the device suggesting a proper function of the device, regardless of its position. It is, however, clear that on the 1st tracing the ventricular electrogram is damped and neither P nor T waves are visible. On the 2nd tracing, the QRS amplitude is slightly higher and a low-amplitude T wave is visible. On the 3rd tracing, the amplitude of the ventricular electrogram is slightly higher, though the T and P waves remain indistinct. On the last tracing, the ventricular electrograms, P and T waves are clearly visible, with minor variations in the morphology and amplitude of the signals. This last position was selected for this patient.

Comments

The Reveal was implanted during a brief procedure performed after anaesthesia of the left subclavian region. The pocket was optimised to be neither to small, which might cause an extrusion of the device, nor too wide, in order to limit the risk of oversensing of motion artefacts. The recordings may be a) triggered by the patient in response to the perception of symptoms, or b) automatic upon the sensing of a bradycardia or tachycardia. In the case of patient-triggered recordings, a clear visualization of P, R and T waves facilitates the recognition of VT versus supraventricular tachycardia, as well as the distinction of sinus pauses versus atrioventricular block. Since automatic recordings rely strictly on the analysis of the ventricular rhythm and count of the R waves, their specificity can easily be lowered by the oversensing of P and T waves.
Therefore, at the time of device implantation, it is critically important to emphasize
1) the sensing of high-amplitude R waves,
2) a reliable visualization of P and T waves, while maintaining high R/T and R/P ratios, and
3) the occurrence of minor variations in the amplitude and morphology of the sensed ventricular signals.
The implantable Holter kit contains a Reveal Vector Check, a mapping tool, which allows the detection of an optimal position without contaminating the device. Data collection must be activated with the programmer before proceeding with the mapping procedure.

Theoritical features / Basic concepts

Basic concepts System overview Implantation Programming BASIC CONCEPTS Since its introduction, approximately 15 years ago, the Implantable Loop Recorder (ILR) has become the reference tool for the diagnosis of unexplained syncope. Syncope is a major public health concern as, in a lifetime, between 40 and 50% of the general population suffer ≥1 episode(s), which account for 1 to 6% of all hospitalisations. While a thorough history and physical examination can ascertain the diagnosis in the majority of patients who present with neurocardiogenic syncope, the yield of conventional diagnostic investigations is far lower in the case of syncope of cardiac origin. While a correlation between symptoms and electrocardiographic recordings is the gold standard, it remains difficult to confirm with...