Thursday, 28 June 2012

- Temporary cardiac Pacemakers.

Temporary cardiac Pacemakers.

Temporary Pacemakers may be:-
  1. Epicardial pacing:- is used during open heart surgery when the surgical procedure create atrio ventricular block. The electrodes are placed in contact with the outer wall of the ventricle (epicardium) to maintain satisfactory cardiac output until a temporary transvenous electrode has been inserted.
  2. Transvenous pacing:- Temporary transvenous pacing involves two components, ie obtaining central venous access and intracardiac placement of the pacing wire.A pacemaker wire is placed into a vein (internal jugular vein , subclavian or femoral veins) under sterile conditions, and then passed into the right atrium then right ventricle. The pacing wire is then connected to an external pacemaker outside the body. Transvenous pacing is often used as a bridge to permanent pacemaker placement. It can be kept in place until a permanent pacemaker is implanted or until there is no longer a need for a pacemaker and then it is removed. Transvenous pacing usually done under imaging for proper positioning of the electrodes.
  3. Transcutaneous pacing (TCP), also called external pacing, is recommended for the initial stabilization of hemodynamically significant bradycardias of all types. The procedure is performed by placing two pacing pads on the patient's chest, either in the anterior/lateral position or the anterior/posterior position. The rescuer selects the pacing rate, and gradually increases the pacing current (measured in mA) until electrical capture (characterized by a wide QRS complex with a tall, broad T wave on the ECG) is achieved, with a corresponding pulse. Pacing artifact on the ECG and severe muscle twitching may make this determination difficult. External pacing should not be relied upon for an extended period of time. It is an emergency procedure that acts as a bridge until transvenous pacing or other therapies can be applied

 *Indications of Temporary Pacemakers:
  1. Symptomatic (syncope,confusion,arrest)  bradycardia (<40 b/min) unresponsive to Chemical pacing (e.g. atropine and dopamine).
  2. suppression of drug resistant tachyarrythmia,e.g. SVT,VT
  3. Drug overdose (e.g. Digoxin,B blockers,CCB).
  4. As prophylactic After Acute anterior and inferior MI which is required in Complete AV block,Mobtiz Type I,II Av block.

*Complications:
  1. Dislodged wire 
  2. Pacemaker malfunction e.g Loss of capture, failure to sense.
  3. Local trauma, arrythmias, pneumothorax, cardiac perforation
  4. Site infection and subsequent septicaemia.
*Equipment:
  1. Pacing wire and pulse generator
  2. Connection lead and battery 
  3. A standard dressing pack and a bio-occlusive type dressing
  4. Spare 9v battery
*A quick videos on basics of insertion can be viewed here,here and here
 
*Procedure for Setting Pacing Parameters:

A-Stimulation Threshold Procedure: Stimulation Threshold is The minimum electrical stimulus needed to consistently capture the heart..
  1. Set RATE at least 10 ppm above patient’s intrinsic rate.
  2. Decrease OUTPUT: Slowly turn OUTPUT dial counterclockwise until ECG shows loss of capture.
  3. Increase OUTPUT: Slowly turn OUTPUT dial clockwise until ECG shows consistent capture.
  4. This value is the stimulation threshold.
  5. Set OUTPUT to a value 2 to 3 times greater than the stimulation threshold value.
  6. This provides at least a 2:1 safety margin.
  7. Restore RATE to previous value. 
B-Sensing Threshold Procedure
"Sensing" is the ability of the pacemaker to “see” when a natural (intrinsic) depolarization is occurring ,a safe method of assessing ‘sensitivity’ is:
  1. Reducing the ppm (pulse per minute) rate approximately 10 below the intrinsic rate
  2. Turning the output to minimum then
  3. Gradually reducing sensitivity and awaiting ‘capture’
  4. Halve the sensitivity, ie if capture achieved at 4 mV set sensitivity to 2 mV
  5. This provides at least a 2:1 safety margin.
  6. Restore RATE to previous value.

* post procedure care: 
- CXR:
  •  to rule out pneumothorax.
  •  to confirm the site of the wire
- 12 lead ECG.
- Continous monitoring.


 Dr Ibrahim Samaha

*Further reading & references:
  1. Oxford handbook of Clinical Medicine, 8th Edition,2010.
  2. Murphy JJ; Problems with temporary cardiac pacing. Expecting trainees in medicine to perform transvenous pacing is no longer acceptable. BMJ. 2001 Sep 8;323(7312):527.
  3. McCann P; A review of temporary cardiac pacing wires. Indian Pacing Electrophysiol J. 2007 Jan 1;7(1):40-9.
  4. Temporary Cardiac Pacing,Intensive Care Evidence Based Practice Guidelines ,2004.
  5. Gammage MD; Temporary cardiac pacing. Heart. 2000 Jun;83(6):715-20.
  6. Deanna J. Tanner: Medtronic, Inc., Minneapolis, MN,December 2007

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