As explained in Part 2 of this review, if the sensitivity value is too low i.It is occasionally impossible to re-establish capture once it has been lost — leading to potential disaster if the underlying rhythm is inadequate. Thresholds Medtronic 5. Page 56 Medtronic Figure The sensitivity number is increased making the pacemaker less sensitive until the sense indicator stops flashing. The different pacing modes and other variables that can be adjusted are the subject of the second part of this review.
Page 64 Medtronic Figure Temporary transvenous wires are more commonly used to stimulate ventricular depolarisation. Most institutional protocols recommend leaving the pacing generator set at half the pacing threshold, to allow for detection of abnormally small signals, and for the possibility that peri-lead fibrosis over the course of the day will reduce the current transmitted to the pacemaker. Loss of ventricular capture ms 5. Connect the temporary pacemaker to the patient lead system.
The threshold adjustment depends on the type of event that precedes the adjustment. This is much more helpful than attempts at analysing the moving screen image. This creates the potential for microshock-induced arrhythmia, particularly ventricular fibrillation. If full pacing is again required, it can be commenced with the confidence that the pacing threshold will not have become too excessive. High dose systemic steroids are sometimes given to patients whose permanent pacemaker wires exhibit rapidly increased thresholds in the first few days.
Page 62 Medtronic The change takes effect within the next two pacing cycles. Asynchronous pacing types and modes Asynchronous pacing type Pacing mode Result Dual chamber Pacing occurs in the atrium and ventricle. In practice, the optimal heart rate is rarely accurately titrated to cardiac output and is usually left at 80—90 beats. Page 57 Medtronic Figure
As bipolar electrodes require less energy to begin with, they may have a greater longevity in pacing compared to a unipolar system [ 12, 13 ]. Navigate to the Pacing Parameters menu. Procedures for finding atrial and ventricular sensing and stimulation thresholds are described in this section. This shows a large deflection with atrial depolarisation, but almost no signal with ventricular depolarisation. High dose systemic steroids are sometimes given to patients whose permanent pacemaker wires exhibit rapidly increased thresholds in the first few days.
Set A Sensitivity and V Sensitivity to values that are at least one-half to one-third of the sensing threshold values. Page 64 Medtronic Figure A more detailed treatment of the use of AEGs is presented elsewhere [ 16 ]. Alternatives to epicardial pacing wires Epicardial wires are not the only means of temporary pacing after cardiac surgery. Typical settings are shown in Table 2. Set Sensitivity to half or less the threshold value. Analysis of the AEG is useful in a number of situations, particularly in some forms of heart block. Unfortunately, the only remedy for increased resistance is the application of increased current or voltage — which further increases the inflammation. Other than minimising the initial energy delivered to the wire, techniques employed to extend wire longevity include variations in placement site which must be balanced against haemodynamic optimisation and the use of steroids.
Typical settings are shown in Table 2. However, increased cardiac output driven by heart rate comes at the cost of increased oxygen consumption. In most cases this filters out the brief pacemaker spike, making it difficult to tell whether a pacing stimulus is being delivered. Navigate to the Mode Selection menu and select the appropriate pacing mode for the patient leads that are connected to the patient. Procedures for finding atrial and ventricular sensing and stimulation thresholds are described in this section. Though seldom used, in some circumstances the atrial electrogram may be the best method of differentiating atrial and junctional arrhythmias, and in defining the nature of an AV block. Page 65 Medtronic Figure Page 47 Medtronic 5. As explained in Part 2 of this review, if the sensitivity value is too low i. Pacing Parameter Adjustments Medtronic Figure Determine the atrial or ventricular stimulation thresholds after determining sensing thresholds. If it is safe to check the pacing threshold, the pacemaker rate should be set above the patient's endogenous rate, such that the chamber of interest is being consistently paced.
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