Hardware for the Heart: The Increasing Impact of Pacemakers, ICDs, and LVADs

The pulse generator remains subcutaneous or submuscular in the pectoral region. An electrode is advanced into the endocardium of the right ventricle apex; dual-chamber ICDs have an additional electrode placed in the right atrial appendage and biventricular ICDs have a third electrode placed transcutaneously in a branch off the coronary sinus.

At the time of the procedure, the electrophysiology team implanting the ICD will configure the diagnostic and therapeutic options; in particular, the defibrillatory threshold will be determined for each specific patient and the device set up with this value.

Complications

Acute complications in the peri-implantation period range from 4% to 5%.¹⁸ These are similar to other transvenous procedures and include bleeding, air embolism, infection, lead dislodgment, hemopneumothorax, and rarely death (perioperative mortality 0.2%-0.4%).^2,19 Long-term complications may present consistent with other indwelling artificial hardware. Subclavian vein thrombosis with pulmonary thromboembolization, superior vena cava syndrome, as well as lead colonization with infection, are potential complications. superior vena cava thrombosis has been demonstrated in up to 40% of patients. These complications often present insidiously and the clinician should retain a high degree of suspicion.

Infection of the pocket or leads has been observed in up to 7%. Technical causes leading to inappropriate shock include faulty components, oversensing of electrical noise, lead fracture, electromagnetic interference, oversensing of diaphragm myopotentials, oversensing of T-waves, and double counting of QRS complexes.²²

Lead complications can include infection, dislodgement (most will occur in the first 3 months after placement), fracture, and insulation defects. Lead failure rates have been reported at up to 1% to 9% at 2 years and as high as 40% at 8 years. Failure occurs secondary to insulation defects (26%), artifact oversensing (24%), fracture (24%), and 26% of the time secondary to infection.^3,23

Cardiac perforation is uncommon but potentially devastating. These cases almost always occur with lead manipulation or repair of a screw in the lead; this rarely would lead to clinical significance but possibly the most emergent manifestation would be cardiac tamponade. Chest pain with signs and symptoms of tamponade require prompt diagnosis. Suspect this in the patient with a newly  paced RBBB pattern on ECG, diaphragmatic contractions (hiccups), and pericardial effusion. Eighty percent of such perforations with tamponades will occur in first 4 days after implantation, and a chest X-ray or the echocardiogram can help confirm the diagnosis.

Pulse-generator complications include migration, skin erosion, and premature battery depletion.²⁴ Twiddler’s syndrome after pacemaker insertion is a well-described syndrome in which twisting or rotating of  the device in the pocket (from constant patient manipulation) results in device malfunction, and Boyle et al describe a similar scenario occurring after ICDs are implanted.²⁵ The authors suggest that an increase in bradycardic pacing threshold or lead impedance may be the initial presentation; however, the possibility that the device failed to sense or treat arrhythmias also should be considered.

Lastly, several studies have documented a statistically significant adverse effect on quality of life in patients living with ICDs. Patients often describe a shock as “being struck by a truck”.²² This may result in depression and anxiety; both are especially prevalent in those who receive frequent shocks. It may be important to consider anxiolytics, support groups, or outpatient referral.^2,22,26,27

Management of the Patient With an ICD in the Emergency Department

Patients with ICDs will present to the ED with a variety of complaints, ranging from general/non-specific (eg, dizziness) to life threatening (eg, cardiac arrest). The following section systematizes the approach to these patients.

Frequently, patients with ICDs will present with the complaint of having been shocked. In those patients, the most important initial step is to determine if the shock was appropriate. Initial management should include placement of a cardiac monitor and a rapid 12-lead ECG. A general assessment for the etiology of the shock may reveal a patient’s clinical deterioration, a change in medical therapy, or electrolyte imbalance.² An accurate history of the surrounding events is key in determining the reason for patients presenting after receiving a shock. A history of chest pain or strenuous physical activity that preceded the shock may indicate, respectively, an appropriate shock from cardiac ischemia or an inappropriate shock caused by skeletal muscle activity. Also, presentations such as a fall following an episode of syncope may represent an ICD-related event and this possibility needs to be considered during the management of these patients.

Clinically Stable Patients After Isolated Shocks

For the patient who received an isolated shock and afterwards is asymptomatic, perform a general assessment as above. Often these patients have experienced an episode of sustained VT that was appropriately recognized and treated.¹ For those who feel ill following a shock, emergent assessment is required for the possibility of a resultant arrhythmia following inappropriate shock (eg, device malfunction or battery depletion) or underlying active acute medical illness such as acute coronary syndrome. Always consider interrogation of the device, which will confirm appropriate shock delivery and successful termination of VT/VF. Interrogation also may reveal signs of altered impedance, which may be treated by ICD reprogramming or lead revision in the case of lead malfunction.² Look for alternative explanations for inappropriate shocks. For example, obtain a chest X-ray to assess proper position of pulse generator or look for presence of lead fracture or migration. Lead fractures tend to occur at three sites: (1) the origin of the lead at the pulse generator, (2) the venous entry site, and (3) within the heart. A basic metabolic panel may reveal hypokalemia or hypomagnesemia leading to lower threshold for dysrhythmia. It is also important to inquire about new medication regimens. Patients with ICDs also are often on multiple cardiac medications, which could lead to alteration in the QT interval or to electrolyte imbalance.