Defibrillator Interrogation

What is Defibrillator Interrogation?

Defibrillator interrogation is a painless office check of an implantable cardioverter-defibrillator, usually called an ICD. An ICD is a small device placed under the skin of the chest. It watches your heart rhythm continuously. If a dangerous rhythm develops, it delivers a pacing burst or an electrical shock. Interrogation is the process of reading what that device has recorded. A specialized programmer is held over the skin above the device, and the two communicate wirelessly. The report shows remaining battery life and how well the leads or wires are working. It also lists every abnormal rhythm the device has stored, along with any therapy it delivered. Settings can be adjusted at the same visit if your rhythm or your medications have changed. Nothing is injected and no needle is used. The check takes about 15 to 30 minutes, and you can drive yourself home afterward. Dr. Vimal Nanavati reviews the findings with you before you leave.

Why Dr. Nanavati may recommend this

An ICD is a safety net, and a safety net needs checking. Interrogation confirms that the device will work when you need it. It also gives a detailed record of what your heart has been doing between visits.

Interrogation is recommended:

• On a regular schedule, commonly every three to six months, sometimes alternating with remote transmissions from home.
• Promptly after the device delivers a shock, or after you hear an audible alert or feel a vibration.
• When you have new symptoms such as heart palpitations, dizziness, fainting, or unusual fatigue.
• After implantation, generator replacement, or any lead revision.
• When remote monitoring flags an abnormal reading.
• When battery depletion or a lead problem is suspected.
• Before and after surgery, since electrocautery and some equipment can interfere with the device.
• After a change in medication that affects heart rhythm, or after a hospitalization.

The American Heart Association explains arrhythmias and the devices used to treat them. MedlinePlus provides an overview of pacemakers and implantable defibrillators in plain language.

How to prepare

Very little is required, and nothing about your routine has to change.

• Eat and drink normally. No fasting is needed.
• Take all of your medications as usual, and bring an up-to-date list.
• Bring your device identification card, which lists the manufacturer and model. This matters, because each manufacturer uses its own programmer.
• Wear a top that opens or lifts easily at the upper chest, such as a button-front shirt.
• Write down any symptoms since your last check. Include the date and time of anything that felt like a shock. Timing helps match your experience to the stored recordings.
• Bring records from any recent hospital visit or emergency department care.
• Allow about 30 to 45 minutes for the appointment.
• Your device may transmit from home. If so, make sure the bedside or mobile transmitter has been plugged in and working.

What happens during the procedure

You sit in a chair or lie on an exam table with your chest accessible. Nothing is placed inside your body, and no part of the check is invasive.

A wand is positioned over the skin above your device. Newer systems simply use a nearby antenna. Communication is wireless. Within seconds the programmer displays the device data on screen.

The technician or physician then reviews several things in order. First comes battery voltage and the estimated time to replacement, then the electrical measurements of each lead. Next is the percentage of time the device has been pacing, and last is the log of arrhythmias it recorded. Any shock or pacing therapy delivered is shown with the rhythm strip that triggered it. That lets us judge the reason for it.

Some devices get a brief test, in which small pacing impulses measure thresholds. Most people feel nothing. A few notice a fluttering or a brief awareness of their heartbeat. It stops as soon as the test does.

Settings that need to change are reprogrammed there and then, wirelessly. You feel nothing during reprogramming. No shock is delivered during a routine interrogation.

Recovery and results

There is no recovery period. You get up and go, and you can drive, work, and exercise immediately.

Results are available during the visit. Dr. Nanavati explains the battery status and roughly how long it should last. He also covers whether the leads look healthy and what rhythms the device has recorded. If your ICD delivered a shock, he reviews whether it was appropriate or inappropriate. An appropriate shock treated a genuinely dangerous rhythm such as ventricular tachycardia. An inappropriate one responded to something benign, like a fast rhythm from the upper chambers.

What happens next depends on the findings. Stable results usually mean returning to your normal schedule of checks. Recorded arrhythmias may lead to a medication change, an echocardiogram, or a referral for an ablation procedure. A battery nearing depletion is scheduled for generator replacement well in advance, so it is never an emergency. A lead abnormality may need imaging and, occasionally, a revision procedure.

Risks and safety

Interrogation is among the lowest risk things done in cardiology. The device is only being read and reprogrammed. There is no incision, no needle, no dye, and no radiation.

The realistic discomforts are minor. Some people feel a brief flutter during threshold testing. Lying still with the chest exposed can be mildly awkward. Anxiety is common, particularly for people who have received a shock in the past. It helps to say so, since the visit can then be paced more slowly.

There is a very small chance that a setting change causes a new sensation, such as awareness of pacing. Report it, since settings can be adjusted again.

The important safety points are outside the office. Keep your device identification card with you. Tell any physician, dentist, or surgeon that you have an ICD before a procedure. Keep cell phones and strong magnets away from the device. Avoid leaning over a running engine or industrial equipment with strong electromagnetic fields. Ask before having an MRI, since only certain devices are MRI conditional. If you receive a shock and feel well afterward, call the office promptly. If you receive multiple shocks or feel unwell, call 911.

Related services and conditions

• Ventricular arrhythmias, the rhythms an ICD is designed to treat.
• 7-10 day ambulatory rhythm monitor for symptoms between checks.
• Echocardiogram to assess the heart's pumping strength.
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