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  1. 1. PACEMAKERS provide electrical stimuli to cause cardiac contraction during periods when intrinsic cardiac electrical activity is inappropriately slow or absent. Pacing systems consist of a pulse generator and pacing leads. With permanent systems, endocardial leads are inserted transvenously and advanced to the right ventricle and/or atrium where they are implanted into the myocardial tissue. The pulse generator is placed subcutaneously or submuscularly in the chest wall. Pulse generators contain a battery as well as sensing, timing and output circuits. The battery (most commonly lithium-iodide) typically has a life span of 510 years. Temporary systems use an external pulse generator with leads placed either transcutaneously or transvenously. Transcutaneous leads are the easiest and most convenient to use for rapid application of temporary pacing. Pulse generators can be set to fixed-rate (asynchronous) or demand (synchronous) modes. In the asynchronous mode, impulses are produced at a set rate independent of intrinsic cardiac activity. This
  2. 2. PACEMAKERS mode carries a small but inherent danger of producing lethal dysrhythmias should the impulse coincide with the vulnerable period of the T wave. In the synchronous mode, the sensing circuit searches for an intrinsic depolarization potential. If this is absent, a pacing response is generated. This mode closely mimics intrinsic myocardial electric activity. On demand pacemakers detect spontaneous ventricular activity and the output of the pacemaker is either suppressed or discharged in order to make the impulse fall within the safe period of the QRS complex. Temporary pacemakersTemporary systems use an external pulse generator with leads placed via transvenous or transcutaneous approaches. Transcutaneous leads are the easiest to use but transvenous leads are the most reliable. For transvenous temporary pacing, catheters are inserted through a central venous access and usually require fluoroscopy for proper placement. Semifloating or flexible balloon-tipped catheters can be used in emergencies since they can be positioned using blood flow alone.
  3. 3. PACEMAKERS Transcutaneous external cardiac pacing is beneficial for symptomatic bradycardia and as a consideration for asystole. They also may be of some benefit for overdrive pacing in treatment of certain tachycardias. Most current models have fixed rate and synchronous pacing. Pacing should generally be started in the synchronous mode. Types of pacemaker Unipolar pacemakers: • Permanent leads are either unipolar (where a single contact is made with the heart) or bipolar. • Unipolar systems (ventricular) are used in cases where AV (atrio-ventricular) conduction is likely to return. • When there is normal AV conduction and a SA (sino-atrial) disorder, then the pacing wire is situated in the right atrium. Dual chamber pacemakers: • Have pacing electrodes in both the right atrium and the right ventricle.
  4. 4. PACEMAKERS • They allow maintenance of the physiological relationship between atrial and ventricular contraction and also allows the paced heart to follow the increase in sinus rate that occurs during exercise. Dual-site atrial pacing: • Newer pacing systems have 2 atrial leads, one in the right atrial appendage and the other either in the coronary sinus or at the os of the coronary sinus. • The ventricular lead is in the right ventricle, either at the apex or at the outflow tract. • This system has been proposed as a promising treatment option for prevention of paroxysmal atrial fibrillation. Biventricular pacemakers: • Pacemaker leads are placed in the right atrium, right ventricle and left ventricle. • Useful in the management of patients with heart failure who have evidence of abnormal interventricular conduction (most often evident as
  5. 5. PACEMAKERS left bundle branch block on ECG) which causes deranged ventricular contraction or dyssynchrony. Implantable cardioverter defibrillators (ICDs combined with internal defibrillator): • Designed to directly treat a cardiac tachyarrhythmia. • If a patient has a ventricular defibrillator and the device senses a ventricular rate that exceeds the programmed cut-off rate of the defibrillator, the device performs cardioversion/defibrillation. • Alternatively, the device, if so programmed, may attempt to pace rapidly for a number of pulses, usually around 10, to attempt pace-termination of a ventricular tachycardia. Pacemaker codes- It usually consists of three letters, but some systems use four or five: Letter 1: chamber that is paced (A=atria, V=ventricles, D=dual chamber) Letter 2: chamber that is sensed (A=atria, V=ventricles, D=dual chamber, 0=none)
  6. 6. PACEMAKERS Letter 3: response to a sensed event (T=triggered, I=inhibited, D=dual - T and I, R=reverse) Letter 4: rate responsive features; an activity sensor, e.g. an accelerometer in the pulse generator, in single or dual chamber pacemakers detects bodily movement and increases the pacing rate according to a programmable algorithm (R=rate responsive pacemaker) Letter 5: Anti-tachycardia facilities. Indications for pacing: Indications for a temporary pacemaker: Emergency/acute: 1)Acute myocardial infarction with: • Asystole • Symptomatic bradycardia (sinus bradycardia with hypotension and type I 2nd degree AV block with hypotension not responsive to atropine) • Bilateral bundle branch block (alternating BBB or RBBB with alternating LAHB/LPHB)
  7. 7. PACEMAKERS • New or indeterminate age bifascicular block with first degree AV block • Mobitz type II second degree AV block • After an anterior myocardial infarction, a pacemaker may be used to prevent bi- or trifascicular block, second or third degree AV block. A pacemaker is only indicated in an inferior myocardial infarction if these conduction disturbances are present 2)Bradycardia not associated with acute myocardial infarction: • Asystole • 2nd or 3rd degree AV block with haemodynamic compromise or syncope at rest • Ventricular tachyarrhythmias secondary to bradycardia • 3)Suppression of drug-resistant ventricular tachyarrhythmia or supraventricular tachycardia
  8. 8. PACEMAKERS 4)Drug overdose, e.g. digoxin, b-blockers, verapamil Elective: 1)Support for procedures that may promote bradycardia 2)General anaesthesia with: • 2nd or 3rd degree AV block • Intermittent AV block • 1st degree AV block with bifascicular block • 1st degree AV block and LBBB • 3)Cardiac surgery: • Aortic surgery • Tricuspid surgery • Ventricular septal defect closure • Ostium primum repair
  9. 9. PACEMAKERS 4)Rarely considered for coronary angioplasty (usually to right coronary artery) but may be required for angioplasty-induced bradycardia Indications for a permanent pacemaker • Persisting symptomatic bradycardia. • Complete AV block (Stokes-Adams attacks, asymptomatic, congenital), Mobitz type II AV block, persistent AV block post anterior MI. • Pacemakers may have a role in the suppression of resistant tachyarrhythmias. • Prevention of atrial fibrillation. • Pacemakers have a role in the management of some patients with dilated cardiomyopathy or hypertrophic obstructive cardiomyopathy. Pacemaker complications: 1)Failure to output: no pacing spike is present despite an indication to pace. This may be due to battery failure, lead fracture, a break in lead insulation, oversensing (inhibiting pacer output), poor lead connection at the takeoff from the pacer,
  10. 10. PACEMAKERS and "cross-talk" (i.e. a phenomenon seen when atrial output is sensed by a ventricular lead in a dual-chamber pacer). 2)Failure to capture: pacing spike is not followed by either an atrial or a ventricular complex. This may be due to lead fracture, lead dislodgement, a break in lead insulation, an elevated pacing threshold, myocardial infarction at the lead tip, certain drugs (e.g. flecainide), metabolic abnormalities (e.g. hyperkalaemia, acidosis, alkalosis), cardiac perforation, poor lead connection at the takeoff from the generator, and improper amplitude or pulse width settings. 3)Oversensing: pacer incorrectly senses electrical activity and is inhibited from correctly pacing. This may be due to muscular activity, particularly oversensing of the diaphragm or pectoralis muscles, electromagnetic interference, or lead insulation breakage. 4)Undersensing: pacer incorrectly misses intrinsic depolarisation and paces despite intrinsic activity. This may be due to poor lead positioning, lead
  11. 11. PACEMAKERS dislodgment, magnet application, low battery states, or myocardial infarction. 5)Pacemaker tachycardia. 6)Pacemaker syndrome is a phenomenon where a patient feels symptomatically worse after pacemaker placement and presents with progressively worsening symptoms of congestive heart failure (CHF). This is mainly due to the loss of atrioventricular synchrony whereby the pathway is reversed and now has a ventricular origin. The atrial contribution to the preload is lost and cardiac output as well as blood pressure fall. 7)Twiddler's syndrome: Some patients will persistently disturb and manipulate the pacemaker generator resulting in malfunction. A chest radiograph may reveal twisting or coiling, or lead fracture, dislodgement, or migration. This situation will require surgical correction with further patient education and counseling. 8)Operative failures: • Pneumothorax (may require chest drain)
  12. 12. PACEMAKERS • Pericarditis • Infection • Haemothorax • Air embolism • Erosion of the pacer through the skin (rare requires pacer replacement and systemicantibiotics) • Haematomas (may require drainage) • Lead dislodgment - usually occurs within 2 days following implantation of a permanent pacer and may be seen on chest radiography (if the lead is floating freely in the ventricle, malignant arrhythmias may develop) • Venous thrombosis - rare and usually presents as unilateral arm oedema
  13. 13. PACEMAKERS Single-chamber Ventricular Pacemaker Single chamber Atrial Pacemaker
  14. 14. PACEMAKERS Dual Chamber Pacemaker