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Published on July 01, 2018

ICMs Help Diagnose Silent AFib and Cause of Syncope

Insertable Cardiac Monitor

ICMs are noninvasive, leadless devices about one-third
the size of a AAA battery. Source: Medtronic

Insertable cardiac monitors are proving highly effective in preventing secondary strokes and determining the cause of infrequent, unexplained syncope.

Secondary Stroke Prevention

Of the 800,000 ischemic strokes that occur annually in the U.S., approximately 200,000 of them are cryptogenic and have no identifiable cause. Although, atrial fibrillation is the suspected cause in many cases. Long-term monitoring with ICMs in people diagnosed with cryptogenic stroke or transient ischemic attack often detect intermittent, asymptomatic AFib that would otherwise not be found by brief cardiac telemetry monitoring, which is the standard of care after a stroke.

“The majority of cryptogenic stroke patients are given a 30-day event monitor and treated with antiplatelet agents,” said Michael W. Farrar, MD, FACC, FASE, a cardiologist with Meritas Health Cardiology. “However, studies show that if you implant a cardiac monitor in these patients, after an average of 100 days, 25%-30% of them will present with silent atrial fibrillation, increasing their risk for secondary stroke. Their treatment plan may need to be adjusted to include anticoagulants, which are more effective at preventing stroke.”

In a recent study, 1,247 cryptogenic stroke patients (65.3 ± 13 years, 53% male) received an ICM and were monitored for 12 months. At the end of the monitoring period, the diagnostic yield was 16.3%, and the median time to detection of the first AFib episode was 86 days.

“You have to monitor these patients for a while to find atrial fibrillation,” Dr. Farrar said. “With a 30-day event monitor, the diagnostic yield would have been 4.6%.”

Unexplained Syncope

Syncope accounts for 740,000 Emergency Department visits each year and 237,000 hospital admissions. Nearly 50% of people hospitalized for syncope do not receive a diagnosis. Patients see an average of three different specialists and often undergo a minimum of 13 diagnostic tests.

“In its guidelines for patients with syncope, the American College of Cardiology indicates routine laboratory testing and cardiac imaging are actually not useful evaluation tools for patients with syncope unless cardiac etiology is suspected,” Dr. Farrar noted. Diagnosis is critical because risk of death increases twofold for people with syncope with a cardiac cause, and the six-month mortality rate is more than 10%.

“If someone faints frequently, we can figure that out. When someone faints once every six months, it’s harder,” Dr. Farrar said.” You’re probably not going to find anything with a 24-hour Holter monitor, but you might with a long-term ICM.”

A recent study involving 570 patients (61 ± 17 years, 54% women) investigated the effectiveness of ICMs in diagnosing recurrent unexplained syncope. During the study period, 218 patients experienced an episode of syncope. The ICM played a role in diagnosing recurrent syncope in 170 (75%) of those patients, 128 (75%) of which were cardiac related.

“Conversely, if a patient experiences syncope with an ICM and does not have ventricular tachycardia, asystole or an atrioventricular block, then the physician can rule out a cardiac-related syncope,” Dr. Farrar added. “The monitors help physicians rule out various causes.”

Monitoring Selection Criteria: The Right Device for the Right Patient

Diagnostic choice should be based on frequency of symptoms and nature of syncope events.

Device Patient Selection Duration
Holter Monitors Daily Symptoms 24-48 hours
Extended Holters Weekly symptoms 2-14 days
External Loop Recorders Monthly symptoms (some up to 6 wks) Up to 1 month
Mobile Cardiac Telemetry Monthly symptoms Up to 1 month
Insertable Cardiac Monitors Recurrent, infrequent symptoms <3 years

Source: Shen WK, et. al., J Am Coll Cardiol. 2017.

The Device

About one-third the size of a AAA battery, ICMs are noninvasive, leadless devices that monitor heart rhythm for up to three years. An electrophysiologist implants the device just under the skin in the fourth intercostal space, 45° relative to the sternum during a 10-minute bedside or outpatient procedure.

Patient benefits include:

  • Easy data download to physician’s office
  • Increased compliance
  • Minimally invasive insertion and removal procedure
  • MRI compatibility

Data can be transferred from the device to the physician’s office in one of two ways, depending on the ICM brand:

  • Automatic download through a portable device
  • Via an app

Indications for Use

The type of cardiac monitor used is situational. “When determining which monitor is most appropriate for a patient, getting an accurate medical history is the most important thing,” Dr. Farrar emphasized. “When you combine medical history with a physical exam, including orthostatic blood pressure checks, and an electrocardiogram, the results dictate what the patient needs.”

ICMs are most effective in people with:

  • Ability to take anticoagulation medications or get a WATCHMAN™ device
  • Cryptogenic stroke diagnosis
  • Increased likelihood of arrhythmic events
  • Infrequent, unexplained syncope with a suspected cardiac etiology
  • Reasonable likelihood of:
    • Embolic etiology
    • Meaningful long-term
    • Survival
    • Paroxysmal AFib

“North Kansas City Hospital began using the technology in 2009 when it was new,” Dr. Farrar said. “Over time, the devices have become much smaller. Based on recent studies and patient outcomes, we are looking into increasing our use of ICMs. It’s amazing technology that is vastly underutilized.”

Michael W. Farrar, MD, FACC, FASE

Michael W. Farrar, MDDr. Farrar received his medical degree from the University of Missouri School of Medicine-Kansas City. He completed his residency and a cardiology fellowship at the University of Cincinnati Medical Center.