Pacemakers and Pacing

There are separate articles on Pacemaker Syndrome and Pacemaker Complications, Inserting Temporary Pacemakers, and Implantable Cardioverter Defibrillators.

• 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.
• Pacemaker output generally stimulates the cavity of the right atrium and/or right ventricle (endocardial pacing). Alternatively, epicardial leads can be implanted surgically onto the heart's surface.
• The battery most commonly used in permanent pacers has a life span of 5 to 9 years.¹

• The pulse generator is internal in permanent pacemakers (subcutaneously or submuscularly) and external in temporary pacing.
• Can be set to a fixed-rate (asynchronous) or demand (synchronous) mode.
• In the fixed-rate mode, there is a small risk of producing dangerous dysrhythmias if the impulse coincides with the vulnerable period of the T wave.
• 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.

• 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.
  • 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.³
• 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 left bundle branch block on ECG) which causes deranged ventricular contraction or dyssynchrony.⁴
• 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.

The North American Society of Pacing and Electrophysiology and the British Pacing and Electrophysiology Group have developed a code to describe various pacing modes. 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)
• 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

A pacemaker in VVI mode denotes that it paces and senses the ventricle and is inhibited by a sensed ventricular event. The DDD mode denotes that both chambers are capable of being sensed and paced.

Indications for a temporary pacemaker⁵

• Emergency/acute:
  • 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)
    • 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 tri-fascicular block, second or third degree AV block. A pacemaker is only indicated in an inferior myocardial infarction if these conduction disturbances are present
  • 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
  • Suppression of drug-resistant ventricular tachyarrhythmia or supraventricular tachycardia
  • Drug overdose, e.g. digoxin, b-blockers, verapamil
• Elective:
  • Support for procedures that may promote bradycardia
  • 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
  • Cardiac surgery:
    • Aortic surgery
    • Tricuspid surgery
    • Ventricular septal defect closure
    • Ostium primum repair
  • Rarely considered for coronary angioplasty (usually to right coronary artery) but may be required for angioplasty-induced bradycardia

Indications for a permanent pacemaker²

• 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.^1,3
• Pacemakers have a role in the management of some patients with dilated cardiomyopathy or hypertrophic obstructive cardiomyopathy.¹

NICE recommends that dual-chamber pacemakers can be used to treat symptomatic bradycardia in people with sick sinus syndrome, atrioventricular block, or both, but that there are a number of special circumstances where dual-chamber pacemakers should not be used for symptomatic bradycardia.⁶

• Temporary 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. Semi-floating or flexible balloon-tipped catheters can be used in emergencies since they can be positioned using blood flow alone.
  • 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.

See separate article Pacemaker Syndrome and Pacemaker Complications

• 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, and "cross-talk" (i.e. a phenomenon seen when atrial output is sensed by a ventricular lead in a dual-chamber pacer).
• 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.
• 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.
• Undersensing: pacer incorrectly misses intrinsic depolarisation and paces despite intrinsic activity. This may be due to poor lead positioning, lead dislodgment, magnet application, low battery states, or myocardial infarction.
• Pacemaker tachycardia.
• Pacemaker syndrome: some patients with VVI pacemakers, especially with SA rather than AV disease, will show retrograde ventriculoatrial conduction during ventricular pacing which can cause fatigue, dizziness and hypotension. Pacemaker syndrome is associated with atrial cannon waves caused by simultaneous atrial and ventricular contractions. Replacement with a dual-chamber is required.
• Operative failures:¹
  • Pneumothorax (may require chest drain)
  • Pericarditis
  • Infection
  • Haemothorax
  • Air embolism
  • Erosion of the pacer through the skin (rare - requires pacer replacement and systemic antibiotics)
  • 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

• Driving:⁹
  • The patient must inform the Driver and Vehicle Licensing Agency (DVLA) that they have a pacemaker.
  • For an ordinary driving licence, can start driving again after one week as long as:
    • There are no symptoms such as dizziness or fainting which may affect driving.
    • Patient attends regular check-ups in the pacemaker clinic.
    • Not recently had a heart attack or heart surgery.
  • For LGV (large goods vehicle) or PCV (passenger-carrying vehicle) licence:
    • Patient cannot drive these vehicles for six weeks after the pacemaker is fitted.
    • Can apply for another licence when no longer have any symptoms that would affect driving, e.g. dizziness or fainting.
    • Current licence is replaced with a three-year licence and the patient will have to go to a pacemaker clinic regularly.
• Sports:
  • Should avoid any strenuous activity for about three to four weeks after the pacemaker has been fitted. After that, patient can continue or start most activities and sports.
  • For contact sports, care should be taken to avoid collisions that may damage the pacemaker and a protective pad should be considered.
• Hospitals and medical treatment:
  • Doctor or technician should be informed that patient has a pacemaker before any investigations or treatment.
  • Always show the pacemaker registration card to any doctor or dentist providing treatment.
  • Most pacemaker generators have an x-ray code that can be seen on a standard chest x-ray.
  • Some hospital equipment, including equipment used in surgery, may interfere with pacemakers. The pacemaker may need to be protected during any operation and re-programmed afterwards.
  • Radiotherapy may damage the pacemaker's circuits. The degree of damage is unpredictable and may vary with different systems. But the risk is significant and builds up as the radiation dose increases. The pacemaker should be shielded as much as possible and moved if it lies directly in the radiation field.
  • Magnetic resonance imaging scans can be dangerous with a pacemaker and the patient should not have an MRI scan. If an MRI is absolutely necessary, the pacemaker output in some models can be reprogrammed.
  • Short-wave or microwave diathermy may bypass the pacemaker's noise protection and interfere with or permanently damage the pulse generator.
  • Transcutaneous electrical nerve stimulation (TENS) may sometimes briefly inhibit unipolar pacing, which then requires reprogramming of the pulse generator.
• Outside interference:
  • Most pacemakers are very resistant to outside interference and the pacemaker has special circuits to detect and remove unwanted electrical activity.
  • However devices with risk include anti-theft systems in shops and other business premises and metal detectors. They are unlikely to cause clinically significant symptoms in most patients but patients should not stay nearby for longer than is necessary.
  • Any hand-held metal detector should not be held near the pacemaker any longer than is necessary.
  • Household devices such as shavers, hairdryers and microwave ovens are not be a problem, as long as they are well maintained.
  • Household tools such as drills, mowers and electric screwdrivers can be used normally.
  • A mobile phone or a cordless phone can be used safely, but the phone should be kept more than 6 inches away from the pacemaker. The ear on the opposite side to the pacemaker should always be used, and the phone should not be put in a pocket over the pacemaker.
• Travelling and security systems:
  • Airport screening systems and anti-theft systems in shops and libraries may rarely cause problems and there is also a small chance that the pacemaker may trigger the alarms.
  • The pacemaker registration card should always be carried by the patient.
  • If a patient with a pacemaker has to go through a security gateway, they should go through quickly and not stand close to the gateway for too long.
• At work:
  • Some workplaces have strong electromagnetic fields which can interfere with the pacemaker, e.g. arc-welding.
  • Power-generating equipment, arc welding equipment and powerful magnets (as in medical devices, heavy equipment or motors) can inhibit pulse generators and there is a risk that the pacemaker may not work properly for patients who work closely with or near such equipment.