What to Do When a Pacemaker Delivers Repeated Shocks

June 2008

By Michele G. Sullivan
Elsevier Global Medical News

SAN FRANCISCO - A single shock from an implantable cardioverter defibrillator is usually nothing to worry about - but when a patient presents to the emergency department with multiple shocks, it's time to rev up the response.

"If you have a patient presenting with two or more repetitive shocks, it's considered a medical emergency, and this patient needs a formal device interrogation" to determine whether the shocks were appropriate, said Dr. Amal Mattu of the University of Maryland in Baltimore.

"Get the patient on a cardiac monitor with an external defibrillator nearby; do a work-up for reversible causes of shocks, like electrolyte abnormalities; get the cardiac enzymes and an electrocardiogram; and take a good history of any symptoms that preceded the shocks, like palpitations, syncope, or chest pain," Dr. Mattu said at the 12th International Conference on Emergency Medicine.

Be aware, however, that the shocks will probably cause transient changes in some of these diagnostic measurements, Dr. Mattu said.

Dr. Amal MattuAfter shocks, most patients will have ST elevations or depressions. The changes tend to be low and transient, however, and resolve within 15-20 minutes, he said. If the ECG shows persistent ST changes, the patient has true ischemia that can't be attributed to the shock. Cardiac enzymes are often slightly elevated after a shock but usually subside within 24 hours, he added.

An electrophysiologist or industry technician will have to be called in to interrogate the device; that is the only way to determine whether the shocks were appropriate. A history won't be sensitive or specific enough to make that determination, Dr. Mattu said.

If the ECG shows normal sinus rhythm and the device is still delivering shocks, it's appropriate to deactivate the shock function.

Place a large magnet over the device, and the shock function will be disabled. That can be permanent or temporary, depending on the model. Consider keeping the magnet there until a definitive management is applied, Dr. Mattu added. Two magnets might be necessary to deactivate an implantable cardioverter defibrillator (ICD) in a very obese patient.

Although they're not usually in medical trouble, patients who receive only a single shock might still show up at the emergency department, usually because they're scared and in pain.

"Most patients say that getting a shock is very painful, like getting kicked in the chest," he said.

Current guidelines recommend a screening exam that focuses on the history preceding the shock. "If there weren't any other concerning signs or symptoms--like syncope, shortness of breath, or chest pain--you probably don't even need to check cardiac enzymes or electrolytes," he noted. "Just tell them to follow up with their cardiologist."

The most common causes of inappropriate shock are supraventricular tachycardia (especially in the presence of aberrant conduction), atrial fibrillation, and atrial flutter. But device failures, including fractured leads, insulation damage, and misconnections, can also cause shocks. Most of the time, these will be obvious on a plain chest x-ray, Dr. Mattu said.

The lead can even perforate the myocardium. When that happens, unusual symptoms might develop. Dr. Mattu said he had seen such a condition in a patient with intractable hiccups. The lead was up against the diaphragm and was pacing it, causing the hiccups. Pectoral muscles can be similarly affected, resulting in intractable spasms. Such patients need to be admitted for replacement of the device, he said.

About 8% of patients with an ICD eventually develop a site infection. Early infections occur within 60 days of implantation and are easily recognized by their classic symptoms: fever, as well as pain and erythema at the site.

Late infections are more subtle and because of that, more dangerous. Often, the only complaint is gradually increasing pain. If the ICD has been in place more than a couple of months and the only complaint is gradually increasing pain, "that is an ICD infection until otherwise proven," Dr. Mattu said.

That high index of suspicion is terribly important, Dr. Mattu said, because treatment delay can be deadly. Mortality is more than 60% if the infections are not treated promptly.

Whether early or late, site infections are usually treated with vancomycin, which covers the usual staph and strep culprits, as well as any infections caused by methicillin-resistant <I>Staphylococcus aureus</I>.

Dr. Mattu also offered some pearls for more unusual situations:

  • An ICD patient who presents with sudden right heart failure might have tricuspid valve damage from the pacing wire, which can perforate the leaflets. Such patients need immediate tricuspid valve repair.

  • The subclavian is no place for a central venous line in those patients.

    Instead, the femoral vein is the safest access site. The second choice for venous access would be the contralateral subclavian or the internal jugular. Use the magnet to deactivate the ICD when the wires go in, Dr. Mattu recommended. If possible, insert the line under fluoroscopy to prevent coiling.

  • If an ICD patient presents with cardiac arrest, put the defibrillator paddles or pads in the anterior-posterior position to avoid damaging the pacemaker. If you have to put both pads on the chest, Dr. Mattu noted, try to stay at least 10 cm away from the device.

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