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Emergency and Acute Medicine – Cardiac Pacemakers
Core Concept
A cardiac pacemaker is an electronic device that delivers electrical impulses to stimulate myocardial contraction and maintain an adequate heart rate and cardiac output when intrinsic conduction is inadequate.
Pacing Modalities
Transcutaneous pacing uses external pads placed in anterior–lateral or anterior–posterior positions. Current is increased until electrical and mechanical capture is achieved. This is a temporary emergency measure until definitive therapy is available.
Temporary transvenous pacing involves insertion of a pacing wire via central venous access into the right atrium or ventricle, connected to an external generator. It is typically used as a bridge to permanent pacing or until pacing is no longer required.
Permanent implanted pacemakers consist of a lithium-powered battery (lifespan approximately 7–10 years), a programmable generator, and one or more leads positioned in the right atrium and/or ventricle to sense intrinsic activity and pace as needed.
A pacemaker magnet placed over the generator converts the device to asynchronous pacing. This is useful when pacer spikes are absent on ECG; a reduced magnet rate (≈10% decrease) suggests battery depletion.
Key Terminology
Fixed-rate pacing fires at a preset rate regardless of intrinsic rhythm and is now rarely used.
Demand pacing senses native cardiac activity and delivers impulses only when intrinsic rates fall below a programmed threshold.
Sensing refers to the device’s ability to detect intrinsic cardiac depolarization.
Pacemakers are described using a standardized code; in emergency care, the first three letters are most relevant: the chamber sensed, the chamber paced, and the response to sensing. Common configurations include VVI (single-chamber ventricular pacing) and DDD (dual-chamber pacing).
Common Causes of Pacemaker Complications
Infection of pacemaker components is most often due to Staphylococcus epidermidis or Staphylococcus aureus and may be associated with endocarditis; transesophageal echocardiography is preferred for diagnosis.
Venous thrombosis related to pacing leads is common but usually asymptomatic; pulmonary embolism is rare.
Failure to pace may result from lead fracture or disconnection, oversensing of muscle activity or electrical interference, or gradual battery depletion.
Failure to capture is commonly due to lead dislodgment, including Twiddler’s syndrome, or elevated myocardial pacing thresholds caused by hyperkalemia or ischemia.
Pacemaker-mediated tachycardia occurs in dual-chamber devices via re-entry involving the generator and intrinsic conduction system, typically limited to about 140 bpm.
Runaway pacemaker is rare and characterized by extremely rapid pacing (>200 bpm) due to component failure or battery depletion, often causing hemodynamic instability.
Clinical Presentation
Pacemaker failure may manifest as bradycardia, syncope, hypotension progressing to shock, fatigue, dyspnea from heart failure, ischemic chest pain, or altered mental status.
Pacemaker-induced tachycardia presents with dyspnea, chest pain, lightheadedness, or syncope.
Pacemaker syndrome, usually seen with ventricular-only pacing, results from atrioventricular dyssynchrony and causes palpitations, weakness, exercise intolerance, dyspnea, or syncope.
Focused History and Examination
Key history includes date of implantation, device type, and adherence to routine follow-up and battery checks. Examination should include cardiovascular and pulmonary assessment and inspection of the generator site for signs of infection.
Essential Emergency Evaluation
A 12-lead ECG is critical to identify pacing spikes, capture, sensing abnormalities, or dysrhythmias.
Metabolic evaluation should assess for reversible causes of elevated pacing thresholds.
ECG evaluation with a pacemaker magnet helps assess device function: normal magnet rate suggests intact function, a rate slowed by more than 10% indicates battery depletion, and absence of spikes suggests significant malfunction.
Diagnostic Studies
Laboratory testing includes serum potassium, arterial blood gas, and serum levels of antiarrhythmic drugs when relevant.
Chest radiography evaluates lead integrity and position, identifying fractures, dislodgment, or perforation.
Prehospital Considerations
Obtain and preserve rhythm strips for later analysis.
Initial Stabilization
Administer supplemental oxygen, secure the airway if needed, establish IV access, and treat bradycardia per ACLS protocols. Avoid placing defibrillation pads directly over the pacemaker generator. Initiate transcutaneous pacing in unstable patients.
Definitive Emergency Management
For pacemaker failure with instability, initiate transcutaneous pacing and arrange for temporary transvenous pacing via central venous access, preferably the right internal jugular vein. Confirm capture electrically and mechanically, determine capture threshold, and set output at two to three times this threshold.
Correct reversible causes such as hyperkalemia.
Pacemaker-mediated or runaway tachycardia may require AV nodal blockade, device reprogramming, or, in extreme cases, surgical disconnection of the lead.
Medications
Adenosine 6 mg IV bolus may be used in select tachyarrhythmias, with cardiology guidance.
Disposition Planning
Admission is required for permanent pacemaker malfunction or suspected device-related infection.
Patients may be discharged only if asymptomatic and after formal device interrogation by cardiology.
Follow-Up Strategy
All patients require referral to cardiology or a specialized pacemaker clinic for definitive evaluation and management.
Clinical Pearls and Pitfalls
Always consider pacemaker malfunction in patients presenting with unexplained bradycardia, syncope, or decompensated heart failure. Early use of a pacemaker magnet is a simple and valuable diagnostic tool in the emergency setting.
Core Concept
A cardiac pacemaker is an electronic device that delivers electrical impulses to stimulate myocardial contraction and maintain an adequate heart rate and cardiac output when intrinsic conduction is inadequate.
Pacing Modalities
Transcutaneous pacing uses external pads placed in anterior–lateral or anterior–posterior positions. Current is increased until electrical and mechanical capture is achieved. This is a temporary emergency measure until definitive therapy is available.
Temporary transvenous pacing involves insertion of a pacing wire via central venous access into the right atrium or ventricle, connected to an external generator. It is typically used as a bridge to permanent pacing or until pacing is no longer required.
Permanent implanted pacemakers consist of a lithium-powered battery (lifespan approximately 7–10 years), a programmable generator, and one or more leads positioned in the right atrium and/or ventricle to sense intrinsic activity and pace as needed.
A pacemaker magnet placed over the generator converts the device to asynchronous pacing. This is useful when pacer spikes are absent on ECG; a reduced magnet rate (≈10% decrease) suggests battery depletion.
Key Terminology
Fixed-rate pacing fires at a preset rate regardless of intrinsic rhythm and is now rarely used.
Demand pacing senses native cardiac activity and delivers impulses only when intrinsic rates fall below a programmed threshold.
Sensing refers to the device’s ability to detect intrinsic cardiac depolarization.
Pacemakers are described using a standardized code; in emergency care, the first three letters are most relevant: the chamber sensed, the chamber paced, and the response to sensing. Common configurations include VVI (single-chamber ventricular pacing) and DDD (dual-chamber pacing).
Common Causes of Pacemaker Complications
Infection of pacemaker components is most often due to Staphylococcus epidermidis or Staphylococcus aureus and may be associated with endocarditis; transesophageal echocardiography is preferred for diagnosis.
Venous thrombosis related to pacing leads is common but usually asymptomatic; pulmonary embolism is rare.
Failure to pace may result from lead fracture or disconnection, oversensing of muscle activity or electrical interference, or gradual battery depletion.
Failure to capture is commonly due to lead dislodgment, including Twiddler’s syndrome, or elevated myocardial pacing thresholds caused by hyperkalemia or ischemia.
Pacemaker-mediated tachycardia occurs in dual-chamber devices via re-entry involving the generator and intrinsic conduction system, typically limited to about 140 bpm.
Runaway pacemaker is rare and characterized by extremely rapid pacing (>200 bpm) due to component failure or battery depletion, often causing hemodynamic instability.
Clinical Presentation
Pacemaker failure may manifest as bradycardia, syncope, hypotension progressing to shock, fatigue, dyspnea from heart failure, ischemic chest pain, or altered mental status.
Pacemaker-induced tachycardia presents with dyspnea, chest pain, lightheadedness, or syncope.
Pacemaker syndrome, usually seen with ventricular-only pacing, results from atrioventricular dyssynchrony and causes palpitations, weakness, exercise intolerance, dyspnea, or syncope.
Focused History and Examination
Key history includes date of implantation, device type, and adherence to routine follow-up and battery checks. Examination should include cardiovascular and pulmonary assessment and inspection of the generator site for signs of infection.
Essential Emergency Evaluation
A 12-lead ECG is critical to identify pacing spikes, capture, sensing abnormalities, or dysrhythmias.
Metabolic evaluation should assess for reversible causes of elevated pacing thresholds.
ECG evaluation with a pacemaker magnet helps assess device function: normal magnet rate suggests intact function, a rate slowed by more than 10% indicates battery depletion, and absence of spikes suggests significant malfunction.
Diagnostic Studies
Laboratory testing includes serum potassium, arterial blood gas, and serum levels of antiarrhythmic drugs when relevant.
Chest radiography evaluates lead integrity and position, identifying fractures, dislodgment, or perforation.
Prehospital Considerations
Obtain and preserve rhythm strips for later analysis.
Initial Stabilization
Administer supplemental oxygen, secure the airway if needed, establish IV access, and treat bradycardia per ACLS protocols. Avoid placing defibrillation pads directly over the pacemaker generator. Initiate transcutaneous pacing in unstable patients.
Definitive Emergency Management
For pacemaker failure with instability, initiate transcutaneous pacing and arrange for temporary transvenous pacing via central venous access, preferably the right internal jugular vein. Confirm capture electrically and mechanically, determine capture threshold, and set output at two to three times this threshold.
Correct reversible causes such as hyperkalemia.
Pacemaker-mediated or runaway tachycardia may require AV nodal blockade, device reprogramming, or, in extreme cases, surgical disconnection of the lead.
Medications
Adenosine 6 mg IV bolus may be used in select tachyarrhythmias, with cardiology guidance.
Disposition Planning
Admission is required for permanent pacemaker malfunction or suspected device-related infection.
Patients may be discharged only if asymptomatic and after formal device interrogation by cardiology.
Follow-Up Strategy
All patients require referral to cardiology or a specialized pacemaker clinic for definitive evaluation and management.
Clinical Pearls and Pitfalls
Always consider pacemaker malfunction in patients presenting with unexplained bradycardia, syncope, or decompensated heart failure. Early use of a pacemaker magnet is a simple and valuable diagnostic tool in the emergency setting.
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