Pacemaker Learning Package
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P a g e SENSITIVITY SENSITIVITY Is the pacemaker’s ability to sense a patient’s intrinsic rhythm or when natural depolarisation is occurring The sensitivity number represents the minimum size, in millivolts, of an electrical signal that will be detected by the pacemaker The higher the sensitivity (number) the less likely the pacemaker will see the patients rhythm Sensitivity The higher the numerical value of the sensitivity, the less sensitive the pacemaker is. The pacemaker looks for any intrinsic event with an amplitude greater than the sensitivity value. In the example above anything over the dotted line is what the pacemaker see’s. 2.5 1.25 0.5 Figure 20: Temporary Cardiac Pacing.ppt P.Nekic Looking at the ECG trace the p waves (which represent atrial excitation) only have amplitude of 2-3mm. The sensitivity setting for atrial pacing is 0.2 -10mV. If the sensitivity setting goes above the amplitude of the intrinsic p wave the pacemaker will no longer be able to see the intrinsic p wave so then it will pace the atrium in a asynchronous mode, i.e it will pace the atrium regardless of the patients underlying rhythm Liverpool Hospital Intensive Care: Learning Packages Intensive Care Unit Pacemaker Learning Package LH_ICU2016_Learning_Package_Pacemaker_Learning_Package 33 | P a g e The same goes for the QRS complex (which represents ventricular contraction). The sensitivity setting for ventricular pacing is 2-20mV. So if the sensitivity setting goes above the amplitude of the QRS complex it will pace the ventricle asynchronously. In the above example the higher the fence the less the pacemaker sees. The fence, i.e. the sensitivity setting, blocks the pacemaker’s ability to see the patients underlying rhythm. If the fence/sensitivity is put up to the highest setting the pacemaker becomes asynchronous and the pacemaker will pace regardless If the sensitivity setting is set at a lower setting or the fence is lower then the pacemaker will see the patients underlying rhythm so the pacemaker will pace It is better to have intrinsic activity as it stimulates better contractions, and more effective forward flow of blood, from the chambers of the heart, especially when the atria and ventricles are intrinsically beating in time. |