Residency · Residency · Cardiology

Cardiac Implantable Electronic Devices

Pacemaker Indications

Sinus Node Dysfunction

Symptomatic sinus bradycardia represents a Class I indication for permanent pacing, requiring documented correlation between symptoms such as syncope, presyncope, fatigue, and exercise intolerance and the presence of bradycardia. Chronotropic incompetence, defined as the inability to achieve at least 80% of the age-predicted maximum heart rate, warrants a pacemaker with a rate-responsive feature, programmed in DDDR or AAIR mode. Tachy-brady syndrome involves sinus pauses exceeding 3 seconds after termination of atrial fibrillation or flutter with associated symptoms, and pacemaker implantation enables the use of rate and rhythm control medications that would otherwise worsen the underlying bradycardia. Asymptomatic sinus bradycardia is generally not an indication for pacing, even when the heart rate falls below 40 beats per minute, as this may represent a normal physiologic state in athletes or during sleep.

Atrioventricular Block

Third-degree or complete atrioventricular block is a Class I indication for permanent pacing regardless of symptoms and regardless of the escape rhythm. Second-degree Type II or Mobitz AV block is also a Class I indication due to the high risk of progression to complete heart block and its infranodal location. Second-degree Type I or Wenckebach block warrants pacing when symptomatic with syncope or heart failure or when the level of block is infranodal; asymptomatic Wenckebach block at the AV nodal level with a narrow QRS is generally benign. Two-to-one AV block should be managed based on symptoms and clinical context, with a wide QRS suggesting infranodal pathology consistent with Type II behavior. First-degree AV block may have hemodynamic consequences when the PR interval is extremely prolonged beyond 300 milliseconds, causing pacemaker syndrome-like symptoms from AV dyssynchrony, which can be optimized with DDD pacing to restore appropriate AV timing.

Post-MI Conduction Disease

Persistent complete AV block or Mobitz Type II block after ST-elevation myocardial infarction warrants a permanent pacemaker. Alternating bundle branch block, in which right and left bundle branch block patterns alternate, indicates trifascicular disease and requires permanent pacing. New bundle branch block with transient complete AV block also warrants permanent pacing. An isolated new fascicular block that resolves does not generally require pacemaker implantation.

Special Indications

Patients with neuromuscular diseases such as myotonic dystrophy, Kearns-Sayre syndrome, and Erb dystrophy have a lower threshold for pacing due to the progressive nature of their conduction disease, and pacing should be considered even with first-degree AV block or fascicular block. Post-cardiac surgery AV block should be observed for at least 5 days to allow for potential recovery before proceeding to permanent pacemaker implantation, though earlier intervention is warranted if complete AV block is accompanied by a junctional escape rate below 40 beats per minute. Post-TAVR AV block should be observed for 24 to 48 hours, with persistent high-degree AV block prompting permanent pacemaker placement, while new left bundle branch block without high-degree block may be monitored longer with ambulatory rhythm monitoring.

ICD Indications

Secondary Prevention

Survivors of ventricular fibrillation or hemodynamically significant ventricular tachycardia not attributable to a reversible cause have a Class I indication for ICD implantation. Reversible causes that do not qualify include acute MI within 48 hours with primary ventricular fibrillation from acute ischemia, truly transient electrolyte abnormalities, and drug toxicity. VT with structural heart disease causing syncope is also a Class I indication. A life expectancy exceeding one year with reasonable functional status is required.

Primary Prevention

In ischemic cardiomyopathy, ICD is indicated when the ejection fraction is 35% or below in patients with NYHA Class II to III symptoms at least 40 days post-MI and at least 3 months on guideline-directed medical therapy, as established by the MADIT-II and SCD-HeFT trials. For non-ischemic dilated cardiomyopathy, the same ejection fraction and symptom criteria apply with at least 3 to 9 months on guideline-directed medical therapy. The DANISH trial showed a reduction in sudden cardiac death but not all-cause mortality, with younger patients under 68 years most likely to benefit. Hypertrophic cardiomyopathy ICD indications are based on sudden cardiac death risk factors, with the ESC HCM Risk-SCD calculator recommending implantation when the 5-year risk reaches 6% or greater. ARVC indications include sustained VT, significant right or left ventricular dysfunction, extensive scar, and syncope. LMNA cardiomyopathy warrants consideration of ICD at an ejection fraction below 45% or with non-sustained VT, representing a lower threshold than standard primary prevention criteria. Channelopathies with ICD indications include long QT syndrome with syncope on beta-blockers, Brugada syndrome with spontaneous Type 1 pattern and syncope or VT, and catecholaminergic polymorphic VT with syncope on beta-blocker plus flecainide.

Situations Where ICD is NOT Indicated

ICD implantation is not appropriate in patients with NYHA Class IV symptoms refractory to medical therapy who are not candidates for CRT, mechanical circulatory support, or transplant, as limited life expectancy precludes meaningful survival benefit. It should not be implanted in patients with newly diagnosed HFrEF before guideline-directed medical therapy has been optimized for less than 3 months, as ejection fraction may improve. Implantation within 40 days of MI is not indicated, as demonstrated by the DINAMIT and IRIS trials showing no benefit. ICD is not appropriate for incessant VT or VF, as the device will deliver repeated shocks without addressing the underlying substrate. Significant comorbidity limiting life expectancy to less than one year also precludes ICD benefit.

Device Selection and Programming

Pacemaker Mode Selection

DDD(R) is the standard mode for most indications, maintaining AV synchrony with rate-responsive pacing when chronotropic incompetence is present. AAI(R) is intended for isolated sinus node disease without AV conduction abnormality but is rarely used today because DDD with managed ventricular pacing is preferred given the future risk of AV block development. VVI(R) provides backup pacing for patients with predominantly normal conduction but occasional bradycardia, for atrial fibrillation with slow ventricular response, and in situations where minimizing right ventricular pacing is the priority. VVIR mode is used for permanent atrial fibrillation with complete AV block or slow ventricular response. Minimizing right ventricular apical pacing is critical, as RV apical pacing exceeding 40% is associated with an increased risk of heart failure. Algorithms such as managed ventricular pacing and AV search hysteresis should be activated to promote intrinsic AV conduction.

ICD Programming

Single-zone versus dual-zone programming involves a ventricular fibrillation zone with high-rate detection and aggressive therapy alongside a VT zone with lower-rate detection and tiered therapy featuring anti-tachycardia pacing before shocks. Anti-tachycardia pacing delivers overdrive pacing to terminate monomorphic VT without a shock, is painless, and is successful in approximately 90% of VT episodes. It is programmed as the first-line therapy in the VT zone. Discriminators for differentiating SVT from VT include onset analysis distinguishing sudden from gradual onset, stability assessment comparing regular versus irregular RR intervals, morphology comparison against stored sinus rhythm templates, and evidence of AV dissociation.

Prolonged detection intervals represent a critical programming advance. The MADIT-RIT trial demonstrated that programming longer detection intervals of 30 to 40 beats before therapy delivery reduced inappropriate shocks by 79% and, importantly, reduced all-cause mortality. The ADVANCE III and PROVIDE trials provide further support for prolonged detection to reduce unnecessary therapy.

Subcutaneous ICD (S-ICD)

The subcutaneous ICD is an entirely subcutaneous system with no transvenous leads, consisting of a pulse generator positioned in the left lateral thorax and an electrode along the left sternal border. Its advantages include avoidance of transvenous lead complications such as infection, lead fracture, vascular complications, and tricuspid regurgitation, making it ideal for young patients who will require a device for decades. Limitations include the inability to provide bradycardia pacing, anti-tachycardia pacing, or cardiac resynchronization therapy, and a higher inappropriate shock rate necessitating pre-implant ECG template screening. The automated pre-implant screening algorithm checks multiple surface ECG vectors for adequate R-wave sensing and T-wave rejection. Indications are identical to transvenous ICD but limited to patients without a pacing or CRT indication, and the device is particularly preferred in patients with limited vascular access, prior lead infection, or congenital heart disease with complex anatomy.

<image> A detailed anatomical illustration showing three types of cardiac implantable electronic devices. Three panels side by side. Panel 1 (Dual-Chamber Pacemaker DDD): show the pulse generator in the left pectoral region with two transvenous leads -- one in the right atrial appendage (labeled "RA lead - atrial sensing/pacing") and one at the RV apex or septum (labeled "RV lead - ventricular sensing/pacing"). Include labels for the subclavian vein access, lead fixation mechanism (active fixation screw), and the tip/ring electrodes for bipolar sensing. Panel 2 (Transvenous ICD): similar generator position but larger device; single lead in RV with tip electrode (pacing), ring electrode (sensing), and shocking coils (proximal and distal, labeled "defibrillation coils") shown as thicker segments along the lead. Include the path through SVC to RV. Panel 3 (Subcutaneous ICD): pulse generator in left lateral thorax (larger, positioned over ribs 5-6 at mid-axillary line); subcutaneous electrode running along left parasternal border from xiphoid to manubrium with sensing electrodes and shocking coil labeled. No intracardiac components visible. Each panel should show the heart in a transparent chest with ribs partially visible. Use color coding: blue for pacing leads, red for sensing, yellow for defibrillation components. </image>

Lead and Generator Complications

Lead Malfunction

Lead fracture is most commonly encountered at the subclavian crush point between the first rib and clavicle and presents with oversensing leading to inappropriate shocks from noise, failure to capture, or high impedance. Insulation breach produces low impedance and can cause undersensing or inappropriate sensing. Lead dislodgement is an early complication occurring within days to weeks, manifesting as loss of capture and inability to sense, with chest X-ray showing a displaced lead position. Recalled leads, including the Sprint Fidelis from Medtronic with its elevated fracture rate and the Riata from St. Jude with externalization of conductor cables, require heightened surveillance in affected patients.

Lead Extraction

Indications for lead extraction include device infection, which mandates removal of all components including leads, lead malfunction with limited venous access for a new lead, device upgrade requiring venous patency, and severe tricuspid regurgitation from lead impingement. Techniques employ powered sheaths using laser or mechanical rotating dilator technology to free the lead from encapsulating fibrous tissue, with fluoroscopic and transesophageal echocardiographic guidance. Risks include superior vena cava tear at a rate of 0.3 to 0.5%, cardiac perforation with tamponade, and hemothorax. The procedure should be performed at experienced centers performing at least 30 extractions per year, with cardiac surgery backup recommended. Mortality is less than 0.5% at experienced centers, with a major complication rate of 1 to 2%.

Generator-Related Issues

Battery depletion is monitored through the elective replacement indicator, which signals approaching end of battery life, and end of life, at which point urgent generator replacement is required. Pocket infection presenting with erythema, warmth, drainage, or device erosion through the skin requires complete system explantation including the generator and all leads, with reimplantation on the contralateral side after blood cultures have cleared. Pocket hematoma is more common with anticoagulation or dual antiplatelet therapy and is most often managed conservatively. Aspiration should be avoided due to infection risk. The BRUISE CONTROL trial established that continuing warfarin at a therapeutic INR of 2 to 3 during device surgery reduces clinically significant hematoma compared to bridging with heparin.

Electromagnetic Interference (EMI)

MRI-conditional devices are now the standard, and non-conditional devices can undergo MRI with specific protocols at experienced centers when benefits outweigh risks, per the HRS Expert Consensus. For electrocautery, bipolar modality is preferred over monopolar, and if monopolar is necessary, the current path should avoid the device. Pacemaker-dependent patients should be programmed to asynchronous mode. Radiation therapy can cause device malfunction when directed at the generator, and shielding or relocation of the generator should be considered if it lies within the radiation field. ICD patients should have tachycardia detection disabled during surgery through magnet application or reprogramming to prevent inappropriate shocks from electromagnetic noise.

Remote Monitoring

Technology

Remote monitoring employs wireless transmission of device data to a home monitor, with data uploaded to manufacturer-specific web portals including CareLink for Medtronic, Merlin for Abbott, and Latitude for Boston Scientific. The system generates automatic alerts for lead impedance changes, battery voltage decline, arrhythmia episodes including atrial fibrillation burden and VT or VF events, delivered therapies such as shocks and anti-tachycardia pacing, and pacing threshold changes.

Evidence

The TRUST, CONNECT, and ECOST trials demonstrated that remote monitoring reduces the time to clinical decision for device events from months to days, reduces inappropriate ICD shocks, and improves survival. The 2023 HRS guidelines recommend remote monitoring for all CIED patients as a Class I recommendation, with in-office visits reduced to annual frequency when remote monitoring is functional. The TEM-HF study showed that remote monitoring integrated with heart failure management using thoracic impedance, heart rate, and activity data can guide heart failure therapy and reduce heart failure hospitalizations.

End-of-Life Device Management

ICD Deactivation

ICD deactivation should involve shared decision-making, with discussion of device deactivation initiated when goals of care shift to a comfort-focused approach. Deactivation is not equivalent to euthanasia and should be framed as removing a treatment that no longer aligns with the patient's goals. Deactivation of shock therapy is a painless procedure accomplished through reprogramming to monitor-only mode or magnet taping, and it eliminates the distressing experience of repeated shocks during the dying process. Pacing can be continued or deactivated separately based on patient wishes. Advanced care planning discussions regarding deactivation preferences should occur at the time of ICD implantation and periodically thereafter, with documentation in advance directives. Palliative care collaboration should be incorporated when appropriate.

Key Clinical Pearls

• RV apical pacing > 40% burden is associated with pacing-induced cardiomyopathy -- always use algorithms to minimize ventricular pacing (MVP, AV search hysteresis), and consider CRT upgrade if pacing-dependent with declining EF
• Do NOT implant ICD within 40 days of acute MI (DINAMIT/IRIS) or within 90 days of newly diagnosed non-ischemic DCM -- EF may improve with GDMT, and early ICD does not reduce mortality
• S-ICD is ideal for young patients (channelopathies, HCM, ARVC) who will need the device for decades but do not need pacing -- avoids transvenous lead complications over a lifetime
• BRUISE CONTROL established that continuing warfarin during device implantation is SAFER than bridging with heparin -- apply this to all patients on therapeutic anticoagulation
• Extended detection intervals (MADIT-RIT programming: 30/40 beats for VF zone) significantly reduce inappropriate and unnecessary shocks and improve survival -- always program conservatively
• Every ICD patient should have the deactivation conversation at the time of implant and during routine follow-up -- this proactive discussion avoids distressing shocks during end-of-life care

References

• Kusumoto FM, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients with Bradycardia and Cardiac Conduction Delay. Circulation. 2019;140:e382-e482.
• Al-Khatib SM, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients with Ventricular Arrhythmias and Prevention of Sudden Cardiac Death. Circulation. 2018;138:e272-e391.
• Moss AJ, et al. Reduction in Inappropriate Therapy and Mortality Through ICD Programming (MADIT-RIT). NEJM. 2012;367:2275-2283.
• Birnie DH, et al. Pacemaker or Defibrillator Surgery without Interruption of Anticoagulation (BRUISE CONTROL). NEJM. 2013;368:2084-2093.
• Knops RE, et al. Subcutaneous or Transvenous Defibrillator Therapy (PRAETORIAN). NEJM. 2020;383:526-536.

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