13.3 Implanted Cardiac Devices, LVAD Emergencies & Electrical Storm
Key Takeaways
Placing a magnet over a pacemaker causes asynchronous pacing at a fixed rate; over an ICD it suspends tachytherapy but does not change the pacing mode.
Electrical storm is three or more separate episodes of ventricular tachycardia, ventricular fibrillation, or appropriate ICD shocks within 24 hours.
Preferred therapy for electrical storm is a nonselective beta-blocker (propranolol beat metoprolol in a randomized trial) plus amiodarone, with deep sedation for refractory cases.
A low-flow alarm with high power on an LVAD suggests pump thrombosis, whereas a suction event from hypovolemia or right ventricular failure produces low flow with low power and ventricular ectopy.
Chest compressions are given in LVAD cardiac arrest when there is no perfusion, despite the historical concern about cannula dislodgement.
Pacemakers and Defibrillators in the ICU
Reading the Device
A device interrogation answers four questions: the underlying rhythm, the programmed mode and rates, lead integrity and thresholds, and stored arrhythmia episodes with therapies delivered. Get it early in any patient with an implanted device and a rhythm or hemodynamic problem.
| Malfunction | Appearance | Common causes |
|---|---|---|
| Failure to output | No pacing spikes when expected | Battery depletion, lead fracture, oversensing, generator failure, magnet-mode confusion |
| Failure to capture | Pacing spike without a resulting complex | Lead dislodgement, high threshold from fibrosis, hyperkalemia, acidosis, myocardial infarction, class I antiarrhythmics |
| Oversensing | Inappropriate inhibition of pacing | Myopotentials (shivering, diaphragmatic), electromagnetic interference, lead insulation failure, T-wave oversensing |
| Undersensing | Pacing spikes in a competing rhythm | Low-amplitude signals, lead problems, programming |
| Pacemaker-mediated tachycardia | Endless loop reentry at the upper rate limit | Retrograde atrial conduction in a dual-chamber device; magnet application terminates it |
| Twiddler syndrome | Lead displacement from patient manipulation | Coiled lead on radiograph |
Hyperkalemia deserves special emphasis: it raises the capture threshold and can cause sudden loss of capture in a pacemaker-dependent patient.
Magnets
- Over a pacemaker: asynchronous pacing at a fixed manufacturer-specific rate (commonly 85 to 100 bpm). Useful when oversensing is inhibiting pacing, or during electrocautery.
- Over an ICD: suspends antitachycardia therapy (shocks and antitachycardia pacing) but does not change the pacing mode. This is the tool for repeated inappropriate shocks.
Inappropriate Shocks
Causes include atrial fibrillation with rapid conduction, sinus tachycardia above the detection rate, T-wave oversensing, lead fracture (look for high-frequency noise on the stored electrogram), and electromagnetic interference. Each shock is painful and proarrhythmic. Apply a magnet, treat the underlying rhythm, then arrange reprogramming.
Perioperative and ICU Considerations
- Use bipolar electrocautery when possible, keep the return pad so current flows away from the device, and consider a magnet for a pacemaker-dependent patient.
- MRI requires a conditional system and a specific protocol.
- External defibrillation: place pads at least 8 cm from the generator, preferably anterior-posterior; interrogate the device afterward.
- Cardioversion in a pacemaker-dependent patient can transiently raise thresholds; have transcutaneous pacing available.
- CIED infection: any pocket infection or device-related bacteremia requires complete system extraction; antibiotics alone fail. Obtain blood cultures and a transesophageal echocardiogram for lead vegetations.
Electrical Storm
Definition: three or more separate episodes of ventricular tachycardia, ventricular fibrillation, or appropriate ICD therapies within 24 hours.
Precipitants: acute ischemia, heart failure decompensation, electrolyte disturbance (potassium, magnesium), QT-prolonging drugs, thyrotoxicosis, high catecholamine states, and new or progressive scar.
Treatment sequence:
- Beta-blockade, which is the cornerstone. A randomized comparison found propranolol plus amiodarone superior to metoprolol plus amiodarone for terminating storm, because nonselective blockade counters the catecholamine surge more completely.
- Amiodarone loading (150 mg IV, then infusion). Lidocaine is preferred when ischemia is the driver; procainamide is an option in selected monomorphic ventricular tachycardia.
- Correct reversibles: potassium to 4.0 to 4.5 mEq/L, magnesium, acidosis, and hypoxemia; revascularize ischemia.
- Sedation, up to deep sedation with intubation, reduces sympathetic drive and is a legitimate therapy, not a last resort.
- Reprogram the device: raise detection rates and favor antitachycardia pacing to reduce shocks; apply a magnet while planning.
- Advanced options: stellate ganglion block or thoracic epidural, catheter ablation, mechanical circulatory support to allow mapping, and cardiac sympathetic denervation.
- In polymorphic ventricular tachycardia with a long QT, give magnesium, stop offending drugs, correct potassium, and pace or use isoproterenol to raise the rate. In short-coupled or Brugada-pattern storm, quinidine and isoproterenol are the specific options, and amiodarone is less useful.
Warning
Escalating catecholamines (dopamine, epinephrine, dobutamine) in electrical storm often worsens the arrhythmia. If shock coexists, mechanical circulatory support is preferable to inotrope escalation.
LVAD Emergencies
Continuous-flow devices (HeartMate 3, older HVAD) unload the left ventricle into the aorta without pulsatility.
Assessment basics:
- Blood pressure is mean arterial pressure measured by Doppler opening pressure or an arterial line; the target is usually a mean of 70 to 90 mmHg (hypertension reduces flow and raises stroke risk).
- Pulse oximetry and noninvasive cuffs are often unreliable.
- Learn the four parameters: flow, speed, power, and pulsatility index.
- Always listen over the pump; a change or absence of the hum is critical.
| Scenario | Parameters | Clues | Action |
|---|---|---|---|
| Hypovolemia or suction event | Low flow, low power, low pulsatility index, ventricular ectopy | Bleeding, diuresis, vomiting | Volume resuscitation; reduce pump speed |
| Pump thrombosis | Low flow with high power | Hemolysis (high LDH and plasma free hemoglobin, dark urine), heart failure | Anticoagulation intensification, thrombolysis in selected cases, pump exchange |
| Right ventricular failure | Low flow despite adequate volume | Elevated jugular venous pressure, rising creatinine and bilirubin, low pulsatility | Inotropes, inhaled pulmonary vasodilators, avoid excessive speed, consider RV support |
| Hypertension | Reduced flow | High mean arterial pressure | Afterload reduction |
| Outflow graft obstruction or kink | Low flow, variable power | Imaging | Surgical correction |
Other recurring emergencies:
- Gastrointestinal bleeding from arteriovenous malformations and acquired von Willebrand disease due to loss of pulsatility. Manage with endoscopy, holding anticoagulation temporarily, octreotide in refractory cases, and avoiding over-reversal that risks pump thrombosis.
- Driveline infection: local care, cultures, prolonged antibiotics, surgical debridement; it can seed the bloodstream.
- Stroke, both ischemic and hemorrhagic, is the main cause of disability.
- Aortic insufficiency developing over time creates a circular flow loop and recurrent heart failure.
- Arrhythmia: ventricular arrhythmias are often tolerated hemodynamically because the pump continues, but they still need treatment.
Cardiac arrest with an LVAD: confirm pump function (listen, check parameters, verify power connections and controller). Treat reversible causes, defibrillate and give drugs as usual, and perform chest compressions when there is no perfusion despite a working pump; current guidance accepts the small risk of cannula dislodgement over the certainty of death without circulation. Always contact the implanting center's team early.
A 72-year-old woman with an implantable cardioverter-defibrillator is admitted with sepsis and receives five shocks in 20 minutes. Telemetry during the shocks shows sinus tachycardia at 128 bpm with no ventricular arrhythmia, and the stored electrograms show high-frequency noise on the ventricular channel. What is the most appropriate immediate action?
Place a magnet over the device to suspend tachytherapy while arranging interrogation and reprogramming
Give intravenous amiodarone 150 mg and start an infusion for presumed ventricular tachycardia
Perform emergent surgical explantation of the generator and leads
Administer deep sedation and intubate to reduce the frequency of further shocks
A 59-year-old man with a continuous-flow LVAD presents with fatigue and dark urine. His device shows reduced flow with elevated power consumption. Laboratory studies reveal LDH of 1,850 U/L and elevated plasma free hemoglobin. What is the most likely diagnosis?
A suction event from hypovolemia
Pump thrombosis
Driveline infection with bacteremia
Progressive aortic insufficiency
A 64-year-old man with ischemic cardiomyopathy has received seven appropriate ICD shocks for recurrent monomorphic ventricular tachycardia in 12 hours. Potassium is 4.2 mEq/L, magnesium is 2.1 mg/dL, troponin is flat, and blood pressure is 108/66 mmHg. He is already receiving an amiodarone infusion. Which addition is best supported?
Dobutamine infusion to improve cardiac output and reduce arrhythmia burden
A nonselective beta-blocker such as propranolol, with deep sedation if storm continues
Oral flecainide loading to suppress the ventricular arrhythmia
Increasing the ICD shock energy to maximum output
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