Atropine administration should not interfere with cardiac pacing. If there is a favorable response to atropine, the conduction abnormality is likely in the AV node. However, if the escape rhythm is originating at or below the bundle of His, there is unlikely to be a response to atropine as the more distal conducting system is not as sensitive to vagal stimulation. Response to atropine can be predicted by looking at the QRS morphology on a 12 lead ECG. If the AV block occurs in the AV node or the Bundle of His, the escape rhythm will have a narrow QRS and will likely respond to atropine. Conversely, if the AV block occurs below the bundle of His, the escape rhythm results in a sub-junctional escape rhythm which has a wide QRS and is unlikely to respond to atropine. NOTE: Because atropine can increase cardiac demand, it is contraindicated in patients with complete heart block secondary to myocardial infarction or ischemia.
- Pad Placement and set up: Recommended pad placement for the best capture is anterior/posterior, as shown below. The positive pad is placed posteriorly to the left of the spine, beneath the left scapula. The negative pad is placed anteriorly between the xiphoid process and the left nipple.
Alternatively, the pads may both be placed anteriorly, with the negative electrode placed in the V6 position and the positive electrode to the right of the sternum, under the clavicle.
- Select Mode: Select the pacemaker button on the box and choose between fixed and demand modes. Fixed mode means that the pacemaker will fire at whatever rate you choose, regardless of the patient’s intrinsic rhythm. Demand mode will sense the patient’s intrinsic rhythm and pace only if needed. Most often you will start in fixed mode.
- NOTE: If in demand mode, the leads should be placed for continuous ECG so that the pacemaker can sense the patient’s intrinsic rate to pace accordingly (double set up). This prevents the “R on T” phenomenon.
- Set rate and output: The initial pacing rate should be set to 60 bpm with the current set to 30 milliamperes (mA). Beware that initially, pacemaker spikes may be visualized without resultant cardiac depolarization. The current can be increased by 5-10 mA at a time until capture is seen as a definite QRS complex and T wave following each pacemaker spike (electrical capture). Once capture is achieved, check the patient’s pulse (mechanical capture) and correlate with the pulse oximeter, blood pressure and clinical signs (physiological capture) to ensure that a perfusing rhythm is present. Final output should be set to 10% above threshold level to ensure continued capture. Human studies have shown that the average current necessary to achieve capture is between 65-100 mA in unstable bradycardias and about 50-70 mA in hemodynamically stable patients.