The use of implantable devices are on the rise and may be used for diagnostic monitoring as well as a treatment option. The requirement for MRI in patients is not an absolute contraindication especially with new devices.
Advances in technology have expanded the scope of cardiac devices beyond their formative uses in the treatment of brady-arrhythmias and cardiac syncope. Implantable devices now function not only as life-saving devices, but can serve as diagnostic tools. This article reviews practical themes regarding commonly inserted cardiac devices including implantable loop recorders (ILR), permanent pacemakers, cardiac resynchronisation therapy pacemakers (CRT) and implantable cardiac defibrillators (ICD) individually; exploring the device descriptions, indications, procedure for insertions, complications, monitoring/follow-up, costs and general advice.
Description of device
The ILR is a recording device contained in a metal alloy casing with an internal battery and microchips. They are the size of a small USB stick, or high-school eraser, though there are devices now available more similar in size to a paper clip. An ILR is able to store ECG data when an abnormal rhythm is detected. If a patient experiences symptoms they are able to activate the device, which will retrospectively record the recent heart rhythm. ILR have the advantage of providing high quality, consistent ECG recordings with a battery life of up to 36 months.
ILRs are commonly used in the investigation of unexplained syncope, palpitations and more recently in screening for the presence of paroxysmal atrial fibrillation (PAF) in cryptogenic stroke.
Assessment of patients with intermittent symptoms can be problematic. Holter monitoring over 24–48 hours may be an insufficient duration for monitoring for infrequent symptoms. The diagnostic yield for Holter monitoring is as low as 1–2%.1 The diagnostic yield from an ILR may be up to 40% in syncope,2 and may be as high as 12% in the detection of PAF.3
External loop recorders (also known as event recorders) are disadvantaged by their retrospective data collection and the requirement for patient activation such that a randomised control trial identified sensitivity for clinically significant arrhythmias to be only 14.6%.4 It is therefore essential that if symptoms are infrequent longer term monitoring is recommended.
Procedure for insertion of device
ILR are implanted subcutaneously under local anaesthetic. They are usually implanted in the left pre pectoral region, though occasionally on the right. The average length for the procedure is around 10–15 minutes and is performed under aseptic conditions. Implantation can be covered with antibiotic prophylaxis.
Given the superficial placing of the device, complications are uncommon. There is a risk of bleeding (1%), bruising (1%) and infection relating to insertion. Longer term there can be a risk of tissue erosion (1%). Over- and under- sensing relating to device placement and patient soft tissue can overfill the device memory or reduce the diagnostic detection.
Follow up varies on local policy and is usually via the pacemaker clinic. Interrogation of the device is usually at 6–12 monthly intervals or on patient request or symptoms. Some devices may also be interrogated remotely via the telephone.
Cost can vary between £1,200 and £2,000 depending on the device.5
Anticoagulation is ideally stopped five days prior to the procedure; however, this varies on a case-by-case basis. Patients may return to work and driving after 48 hours. Patients may return to normal activities, eg. bathing, swimming and exercise, once the incision site has healed. It is unlikely that security devices will interfere with data collection, but the metal ILR may set off security devices hence patients should present a device identification card to security to obtain clearance.
MRI scanning is a relative contraindication in patients with an ILR. The magnetic field may corrupt data recorded. It would be advisable to check with a cardiac physiologist prior to scanning as there may be a requirement for reprogramming the device or downloading saved data prior to the scan.
Description of device
A Pacemaker (Figure 2) may be thought of as electronic pulse generator that sends impulses via leads to different chambers of the heart. The type of pacemaker inserted is usually denoted by a series of letters that gives a description of the function of the device (Table 1). The most common types of pacemaker devices include VVIR and DDDR. Battery life may be between five to 10 years.
The PPM could be a single chamber or dual chamber. Single chamber PPM denotes the lead in either one of the right atrium or right ventricle. Dual chamber PPM denotes the lead in the one atrium and one ventricle; and these are used to maintain the synchronous relationship between the atria and ventricles. A bi-ventricular PPM denotes that the leads are placed in right atrium and with pacing of both ventricles; these are used for the treatment of heart failure.
|TABLE 1. A FOR ATRIAL, V FOR VENTRICULAR OR D FOR DUAL|
|First letter||Denotes the chamber paced|
|Second letter||Denotes the chamber that is sensed|
|Third letter||The mode of response to detected action potential and so is directly related to the sensing function. There are three options – Inhibit (I) will mean that if there is a detected intrinsic action potential, the pacemaker will not pace. Trigger (T) this is if an atrial signal is detected, and there is a no intrinsic ventricular response this will trigger a paced ventricular beat. Dual (D) for both these functions.|
|Fourth letter||Denotes programmable features such as Rate response (R), which is the ability of the pacemaker rate to increase with physiological activity. Other programmable features include Communicational (C) and Multi-programmable (M).|
The most common indications for a pacemaker device include symptomatic bradycardia, AV node disturbances and significant pauses. Other indications are set out in Table 2.
Procedure for insertion of device
|TABLE 2. INDICATIONS FOR PPM|
|Significant AV node disturbances with significant pauses (eg. Mobitz type II block, AF with slow ventricular response)|
|As part of therapy for recurrent paroxysmal atrial fibrillation (performed with AV node ablation)|
|Occasionally used in the suppression of resistant tachyarrhythmia|
Broad spectrum intravenous antibiotic prophylaxis is usually administered beforehand and, depending on local policy, patients may receive a course post procedure. The procedure is performed under a local anaesthetic. Venous access is achieved most commonly via the cephalic or subclavian vein. Location of the relevant structures and insertion of a pacing lead are made under fluoroscopic guidance. Constant ECG monitoring is required during the procedure.
Once in place, pacing leads are connected to an external device operated by a cardiac physiologist to temporary pace and confirm ideal positioning of the lead. Checks are made to ensure there is no diaphragmatic stimulation and that leads are stable on coughing and deep breathing. Once all lead placement checks are confirmed the generator box is placed in the pre-pectoral pocket (fashioned using blunt dissection). The device in its pocket is then sutured in several layers.
PPM related complications have been summarised in Table 3.
Post procedure, patients require a check chest x-ray and a post insertion pacemaker check. Follow up is performed in pacemaker clinics with a physiologist; initially at 4–6 weeks followed by 6–12 monthly intervals depending on local policy.
Follow up procedures involves interrogation of the device using a device programmer and reader placed near or on the patient’s chest that communicates with the device using high frequency radio waves ~175kHz ranger. Diagnostic information may be obtained, eg. underlying rhythm, frequency or demand for pacing as well as episodes of tachyarrhythmia.
Pacemaker generally cost around £2,000, but this may vary according to type and available settings.
Patients should avoid lifting with the arm above the shoulder on the side of the pacemaker for four to six weeks. Stitches usually dissolve by themselves within five to seven days. Patients are advised to keep the wound dry for this time.
Driving may resume within a week according to the DVLA providing no further symptoms of syncope or pre-syncope are present however patients with group 2 licences may not drive for six weeks.6
PPM will set off security alarms and patients should be advised not linger within security scanners as it may interfere with the settings.
Modern pacemakers may be “MRI compatible,” but it is essential to ask the patient for the model number that they usually carry in a card. This may be checked with the manufacturer for MRI compatibility.
It should be noted that pacemakers may require pre-scan programming to special mode that would allow an MRI scan followed by a post scan check therefore it is essential to only undertake scans when the services of a cardiac physiologists are available.
If lithotripsy is to be undertaken the pacemaker requires programming pre and post procedure as the electromagnetic fields created by the lithotripsy may cause inappropriate sensing or pacing.
Description of device
Cardiac resynchronisation therapy (CRT) pacemakers are only suitable for 5–10% of patients with heart failure based on current European Society for Cardiology (ESC) Guidance. This device has leads which pace both ventricles to tackle dys-synchrony associated with heart failure. Survival for patients with heart failure is poor, but with CRT one study showed a reduction of six month mortality from 26% to 14%.7
The ESC guidance for consideration of CRT are as follows:8
- Patients with left bundle branch block with a QRS duration >120s with chronic heart failure and an ejection fraction of <35%. Patients should have a functional class of NYHA 2–3 (or 4 if ambulatory) despite adequate medical treatment.
- CRT should be considered in patients with non LBBB wide QRS durations >120ms with LVEF <35% and NYHA symptoms 2–4 despite adequate medical treatment.
- CRT is not recommended for patients with chronic heart failure with QRS <120ms.
Procedure for insertion of device
The insertion procedure is similar to that of a permanent pacemaker device, although CRT procedures are usually undertaken in the tertiary centre setting. Right sided leads are inserted in the same way as with permanent pacing. The left ventricle is paced externally via its lateral wall that is accessed through the coronary sinus, which is located using a preformed guide catheter sometimes with the aid of coronary angiography.
The most common complications are similar to that of permanent pacing (as summarised in Table 3), but with the additional risk of the additional LV lead. Failure of passing the LV lead is between 5–10%.9
This may be with a local cardiology department if they have access to CRT reading equipment, otherwise this may be with the nearest tertiary centre. Follow up is routine every six months with a cardiac physiologist.
A CRT-P pacemaker system has been quoted by NICE as costing £3,411.10
Patients should be advised to continue taking their heart failure medications and that CRT is an adjunct to therapy. Post procedure instructions regarding wound care and return to work are similar as for permanent pacemakers.
The scanning of patients with CRT devices with MRI is strongly discouraged. Newer devices have allowed MRI scans with “exclusion zones”. A newer generation of devices are being developed that is fully MRI compatible.
Description of device
Implantable ICDs are devices capable of treating life threatening arrhythmias with a well timed shock. They also have pacing, diagnostic and cardioversion functions. They serve an important function in the prevention of sudden cardiac death.
ICD are recommended for patients:
- Who have survived a cardiac arrest secondary to ventricular tachycardia or ventricular fibrillation
- Who have had spontaneous ventricular tachycardia causing syncope or haemodynamic compromise
- Who have had sustained ventricular tachycardia in association with a reduced left ventricular ejection fraction (<35%) with NYHA 2/3 symptoms
- Who have a familial cardiac condition with a high risk of sudden cardiac death
- Who have undergone surgical repair of congenital heart disease
- At higher risk of sudden cardiac death—those patients with an MI, LBBB and severe LV dysfunction.
Procedure for insertion of device
For the majority of patients a single ventricular lead is inserted via venous access as with permanent pacing. This is inserted under fluoroscopic guidance and much like in permanent pacing; the electrophysiological parameters are checked with positioning.
Common complications are as for pacemaker insertion (see Table 3). There is the additional risk of inappropriate shocks. This can be a complication of device over sensing or occasionally in the context of atrial fibrillation and the device falsely detecting the high rates as possibly ventricular in origin. This required specialist input and potential device reprogramming/revision.
Routinely every six months in tertiary centres.
NICE quotes the cost of an ICD system as £9,692. Combined CRT-D pacemakers cost £12,293.
General advice is similar to that post PPM insertion. Patients are advised to cease driving for one month after insertion. But if the indication was for secondary prevention (ie. post cardiac arrest) this requires six months off driving. ICD regardless of indication equates complete barring for a Group 2 HGV license. Patients who receive a shock should cease driving for six months. In cases of identified inappropriate shocks patients should cease driving for one month.6
In the event of a cardiac arrest the ICD may be switched off by placement of a magnet (Figure 4) on top of the device to prevent inappropriate shocking. Most Coronary Care Units will have access to this.
|TABLE 3. SUMMARY OF PPM RELATED COMPLICATIONS|
|Lead displacement or fracture||Suspect if increasing in pacing threshold or reduction in ECG amplitude, or inappropriate pacing.
Diagnosis is via CXR and device interrogation.
|Requires specialist cardiology assessment.|
|Pneumothorax 2%||Often asymptomatic and usually picked up during follow up CXR. This is now much less common with operators using Cephalic vein access||Usually medical management may require aspiration of a chest drain depending on size and symptoms.|
|Haemothorax & air embolus||Air embolus or haemothorax may occur during the procedure.||Usually managed by withdrawal of the needle and compression of the artery.
Usually the air is absorbed in the lung. Rarely if the patient becomes haemodynamically compromised may require Intensive care management.
|Lead perforation <1%||May be acute or chronic. Diagnosis is confirmed by echocardiography or CT scan.
Patients usually present with chest pain, hemodynamic compromise or pneumothorax
|In the case of tamponade urgent pericardiocentesis is required. Cases may require management in tertiary cardiothoracic centre.|
|Infection <1%||Either at site or actual device or lead infection||Requires blood cultures and swabs from device site. Initially may require prolonged antibiotics. In some circumstances may require device extraction.|
|Venous thromboembolism||Rarely symptomatic. Watch out for distended veins and signs of SVC obstruction||If asymptomatic does not require treatment. Symptomatic patients require anticoagulation.|
|Twiddlers’ syndrome||This occurs when patients often without realising, move the generator back and forth under the skin causing it to displace.||Instruct patients not to manipulate the device.|
|Skin erosion <1% & haematoma||Bruising and ecchymosis on the site of insertion||Conservative measures usually. If possible to stop anti-platelets or anticoagulation.
In the case of large haematoma may require aspiration or surgical evacuation.
|Skin erosion is more common in the elderly.||It is important to exclude infection causing erosion. If there is no infection then there may be a requirement for implantation at another site. If infection is causing the erosion then there is a requirement for removal of generator and leads to clean the site.|
|Pericarditis <5%||Occur more commonly in patients with active leads.||Patients should be followed up to ensure no pericardial effusion or tamponade occurs.
If there is no pericardial effusion then conservative measures using Colchicine or non-steroidal anti-inflammatory medications may be used. Rarely repositioning of the leads is required.
The diverse range of uses for implantable devices has meant that they have become a crucial tool in the management and treatment of a growing cohort of patients of varying medical backgrounds. A greater appreciation of their uses and complications is imperative in utilising their capabilities and potential.
Dr Tharusha Gunawardena, West Suffolk Hospital NHS Foundation Trust
Dr Sajid Alam, Ipswich Hospital NHS Trust
Dr Naveed Razvi, Ipswich Hospital NHS Trust
Conflict of interests: none declared.