What is pacemaker?• An artificial device that delivers a timed electrical stimulus which results in cardiac depolarization.• Keeps the heart from beating too slow.• Cannot restrict heart from going too fast.
Indications for Temporary Pacing• Sinus Node Dysfunction• Sick Sinus Syndrome• Symptomatic sinus bradycardia• Sinus arrest• SA block
Sinus Node DysfunctionClass I Indications• Sinus node dysfunction with documented symptomatic sinus bradycardia• Symptomatic chronotropic incompetenceClass II Indications• Class IIa: Symptomatic patients with sinus node dysfunction (hr < 40bpm) and with no clear association between symptoms and bradycardia.• Class IIb: Chronic heart rate < 40 bpm in minimally symptomatic patients while awake.Class III Indications• Asymptomatic sinus node dysfunction.
AV Block• First-degree AV block• Second-degree AV block – Mobitz types I and II• Third-degree AV block
AV BlockClass I Indications• 3rd degree AV block associated with: – Symptomatic bradycardia (including those from arrhythmias and other medical conditions). – Documented periods of asystole > 3 seconds. – Escape rate < 40 bpm in awake, symptom-free patients. – Post AV junction ablation. – Post-operative AV block not expected to resolve.• Second degree AV block regardless of type or site of block, with associated symptomatic bradycardia
Class II Indications• Class IIa: – Asymptomatic CHB regardess of level. – Asymptomatic Type II 2nd degree AV block – Asymptomatic Type II 2nd degree AV block within the His-Purkinje system found incidentally at EP study – First-degree AV block with symptoms suggestive of pacemaker syndrome and documented alleviation of symptoms with temporary AV pacing• Class IIb: – First degree AV block > 300 ms in patients with LV dysfunction in whom a shorter AV interval results in haemodynamic improvement.
Class III Indications• Asymptomatic 1st degree AV block• Asymptomatic Type I, 2nd degree AV block at supra-Hisian level• AV block expected to resolve and unlikely to recur (e.g., drug toxicity)
First-Degree AV BlockAV conduction is delayed, and the PR interval isprolonged (> 210 ms or 0.21 seconds)
Second-Degree AV Block – Mobitz I (Wenckebach)Progressive prolongation of the PR interval until aventricular beat is dropped,PR interval = progressively longer until a P-wave fails toconduct
Third-Degree AV BlockNo impulse conduction from the atria to the ventricles,PR interval = variable
Bifascicular and Trifascicular Block (Chronic) – IndicationsClass I Indications• Intermittent 3rd degree AV block• Alternating bundel branch block..Class II Indications• Class IIa: – Syncope not proved to be due to AV block when other causes have been exluded, specifically VT. – Pacing-induced infra-Hisian block that is not physiological, occur during EP STUDY.• Class IIb: Neuromuscular disease with any degree of fascicular block with regardless of symptoms.Class III Indications• Asymptomatic fascicular block without AV block• Asymptomatic fascicular block with 1st degree AV block
Reversible cause that will likely not require permanent pacing.• Injury to the sinus or AV node or His-Purkinje system after heart surgery.• Lyme disease. ("Lyme carditis".)• Cardiac trauma, as occurs after a motor vehicle accident with associated chest trauma, may require temporary bradycardia pacing for transient asystole resulting from AV block that typically improves over time.• Toxic, metabolic, electrolyte, and drug-induced. (hyperkalemia, digoxin toxicity, beta-blocker sensitivity or overdose, and antiarrhythmic drug therapy.)• Subacute bacterial endocarditis with an aortic valve abscess damaging the His-Purkinje system and causing AV block.
• Catheter trauma to the right bundle branch when a left bundle branch block is present has the potential for causing complete heart block.• Other indication: – Coverage for anesthesia and surgery in patients with positive cardiac history. – Treatment for CHB development during Surgery. – Augment cardiac output post operatively.
• Guidelines from the American Heart Association and American College of Cardiology recommend temporary pacing in the following situations in patients with acute myocardial infarction• Symptomatic bradycardia due to sinus node dysfunction or Mobitz type I second degree heart block that is not responsive to atropine therapy• Mobitz type II second degree or complete AV block• Bilateral or alternating bundle branch block including right bundle branch block with left anterior fascicular block or left posterior fascicular block• A new bundle branch block with first degree AV block• An old right bundle branch block with first degree AV block and a new fascicular block
Pacing modalities• Transvenous Endocardial pacing.• Transthoracic Epicardial pacing. – This pacing system is accomplished through electrodes that are loosely attached through the surface of the heart during cardiac surgery. Two or four surgical wires are normally attached to the atrium, ventricle or both. – Two wires that usually exit to the left of the sternum are the ventricular wires and the two that exit to the right of the sternum are the atrial wires. It is important that the atrial wires are inserted into the atrial terminal and the ventricular wires are inserted into the ventricular terminal on the pulse generator .
• Transcutaneous / External pacing.• This system is composed of two adhesive conducting pads that are placed externally on the chest wall. One pad is placed anteriorly to the left of the sternum. The posterior pad is placed directly behind the anterior pad, to the left of the thoracic spine.• The electrodes are incorporated into the pads and cover a large surface area over the skin.• The pads are connected to an external pulse generator This type of pacing may be used as a temporary measure in the event of bradyarrhythmias with poor perfusion and low blood pressure until a transvenous pacing system can be inserted. More energy is used to “pace” the heart externally, potentially causing pain to the patient and therefore require analgesia or sedatives.
How do pacemakers work?• Modes and Codes – NBG Code – Mode Selection – Indications for Pacing – Pacing Modes• Pacing.• Sensing.
NBG Code I II III IV V Chamber Chamber Response Programmable Antitachy Paced Sensed to Sensing Functions/Rate Function(s) ModulationV: Ventricle V: Ventricle T: Triggered P: Simple P: Pace programmable M: Multi-A: Atrium A: Atrium I: Inhibited S: Shock programmableD: Dual (A+V) D: Dual (A+V) D: Dual (T+I) C: Communicating D: Dual (P+S)O: None O: None O: None R: Rate modulating O: NoneS: Single S: Single O: None (A or V) (A or V) Stuart Allen 06
Pacing Systems• One lead implanted in the right atrium• One lead implanted in the right ventricle• Or both.Cable connector.• Connector pins on the lead(s) must be fully inserted in the patient connector block.• Observe polarity• Finger tighten onlyCable to device connection.
• Pacing rate: regulates the number of impulses that can be delivered to the heart per minute. The rate setting depends on the physiological needs of the patient.• Threshold: is the lowest energy, which will cause the myocardial cell to contract. The desired threshold is 0.5- 1.0mA.
Stimulation Threshold Procedure• Set RATE at least 10 bpm above patient’s intrinsic rate.• Decrease OUTPUT: Slowly turn OUTPUT dial counterclockwise until ECG shows loss of capture.• Increase OUTPUT: Slowly turn OUTPUT dial clockwise until ECG shows consistent capture. This value is the stimulation threshold.• Set OUTPUT to a value 2 to 3 times greater than the stimulation threshold value.• This provides at least a 2:1 safety margin.• Restore RATE to previous value.
Sensing• Sensing is the ability of the pacemaker to “see” when a natural (intrinsic) depolarization is occurring. – Pacemakers sense cardiac depolarization by measuring changes in electrical potential of myocardial cells between the anode and cathode. – Expressed in Millivolts (mV).
Sensing Threshold Procedure• Set rate at least 10 bpm below patient’s intrinsic rate.• Adjust output: Set OUTPUT to 0.1 mA .• Decrease SENSITIVITY: Slowly turn MENU PARAMETER dial counterclockwise until pace indicator flashes continuously.• Increase SENSITIVITY: Slowly turn MENU PARAMETER dial clockwise until sense indicator flashes and pace indicator stops flashing. This value is the sensing threshold.• Set SENSITIVITY to half (or less) the threshold value.• This provides at least a 2:1 safety margin.• Restore RATE and OUTPUT to previous values.
Trouble Shooting• Failure to Capture: – Failure to capture means that the heart has not responded to the stimulus . If the pacemaker uses an atrial electrode the spike is followed by a P wave; if the pacemaker uses a ventricular electrode, a QRS complex should follow the spike.• Causes: – Loose connections in the pacemaker system (tighten connections) – Lead wire fracture (replace leads) – Lead dislodgment (reposition pt to left side, gravity may assist only in transvenous) of change leads around from box
• Failure of the pacemaker battery .• Failure of the pulse generator (change pulse generator) .• Inadequate amount of energy is delivered to initiate pacing (Reassess pacing threshold. The output may need to be increased. If this does not work, switch to another pacing lead and reassess pacing threshold• Electrolyte disturbance (check electrolytes) .
A A B B CIdentify: Capture Beats (A) Fusion Beats (B) Pseudofusion Beats (C)
Failure to Sense:• Once appropriate capture has been determined one must establish that the pacemaker is sensing the patient’s intrinsic rhythm appropriately. Sensing means that the pulse generator is able to process (“see”) intrinsic electrical signals . Oversensing : – An electrical signal other than the intended P or R wave is detected. OVERSENSING = UNDERPACING Undersensing : – Pacemaker does not “see” the intrinsic beat, and therefore does not respond appropriately. UNDERSENSING = OVERPACING
Causes of Oversensing.• Skeletal muscle contraction (ensure pt. is not shivering, warm them)• Electromagnetic interference (remove electromagnetic interference e.g. magnetic resonance imaging (MRI), microwave ovens (esp. in old models)• Decrease sensitivity accrodingly.
Causes of undersensing• Tissue ischemia/ischaemic heart disease.• Increased sensing threshold caused by fibrosis at electrode tip or oedema formation.• Electrolyte disturbances (new bundle branch block) .• Poorly positioned lead/dislodgment (position pt on left side, gravity may assist) .• Defected or dead battery.
• Failure to Pace (Fire): – means that the pacemaker does not pace when physiologically indicated. It is recognised by the absence of pacing spike, which reveals the patients underlying intrinsic rhythm . The patient may exhibit hypotension, lightheadedness and syncope if the underlying rhythm is ineffective .• Causes: – Loose connection between lead, wire, cables and pacemaker ( ensure all connections are secure) – Fracture of lead wire (assess integrity of lead wire. If broken, use another lead wire and reassess the pacing threshold) – Failure of battery (change battery) – Failure of pulse generator (change pulse generator) – Oversensing (reassess sensitivity, decrease if needed)
Complication• Complications are not uncommon in patients treated with temporary pacing . Without recognition of the potential complications, adverse effects might outweigh the beneficial effects of the pacemaker.• Serious complications of internal pacing are rare, but are important to recognize, and include, • Lead dislodgement and disconnection. • Bleeding. • Pericardial tamponade. • Thrombophlebitis. • Pulmonary embolism. • Catheter knotting. • Air embolism.
Complication– Various arrhythmias including ventricular tachycardia and ventricular fibrillation.– Electrical hazards, such an inadvertent induction of ventricular fibrillation– Pneumothorax– Subdiaphragmatic stimulation– Infection– Perforation– Asystole.
WHEN TO AVOID TEMPORARY PACING .• When the risks outweigh the benefits.• When there are intermittent, mild or rare symptoms and the bradycardia is well tolerated. This includes symptomatic complete heart block with an adequate and "stable" escape rhythm or symptomatic sick sinus syndrome with only rare pauses.• In the presence of a prosthetic tricuspid valve or right ventricular infarct, a circumstance in which it may not be possible to achieve right ventricular capture.• In a patient with a myocardial infarction who has received a thrombolytic agent and is being aggressively treated with anticoagulation or antiplatelet agents. Even insertion of the catheter by a cutdown of the right internal jugular vein may be associated with significant bleeding in such patients.• When there is no informed consent unless temporary pacing is considered life-saving.
Care of temporary pacemaker.• Often patients post cardiac surgery who have temporary pacing wires in situ will return to the unit from theatre with the following settings - output on full and sensitivity on async. These settings need to be adjusted immediately on return by setting sensitivity – from async to a mV setting and adjusting output accordingly.• Every shift: – Threshold check, record new threshold level. – All electrical equipment is grounded . – Patient is in bed when doing the pacemaker checks as haemodynamic instability may occur . – Continuous ECG monitoring
Care of temporary pacemaker – All connections are secure and tight . – Leads and cable are secure to prevent tension when patient moves. Observe for fractures in the leads . – Record abnormalities, obtain rhythm strip daily. – Avoid MRI scanning . – When pacing is turned off, 12 leads ECG is required. – Daily CXR. – Examine for pericardial friction rub.