Internal Defibrillators

Baran Kilical MD

Content Contributor

Evolution of Internal Defibrillators

There are many varieties of defibrillators. The subcutaneous defibrillators are unique in that they do not require using the venous anatomy. This can be advantageous when there are other competing interests such as using those veins for hemodialysis or vascular ports (ie ports for chemotherapy). Additionally, it makes it easier to remove the wires if this ever becomes necessary.

Transvenous defibrillators are the most common type used and they can also provide pacing capabilities similar to those of a pacemaker. These can be single chamber (wire in right ventricle), dual chamber (wire in right atrium and right ventricle), or biventricular (wire in right atrium, right ventricle, and left ventricle pacing capability).

While all of the defibrillators have the primary function of defibrillation (resetting the heart), many offer additional features. One such feature is thoracic impedance monitoring to assess fluid status. This is used to monitor fluid status for heart failure patients. Others have activity logs, MRI compatibility, and Bluetooth technology to automatically transmit reports for monitoring by your cardiologist.

Technology Spotlight

Medtronic Internal Defibrillator

While all defibrillators do the essential task of delivering a shock to save the patient’s life, Medtronic’s defibrillator has several available unique features including an ergonomic shape, Wavelet algorithm, and Optivol. As the defibrillator is often placed under the skin, the edges of the device can be felt when pressing on the person’s chest. The ergonomic shape sits nicely under the skin. Wavelet is a unique algorithm that helps improve detection of dangerous heart rhythms and distinguish them from abnormal heart rhythms that are not life threatening. While many manufacturers have similar algorithms, Wavelet is the most advanced of the available algorithms. Optivol uses measurements of resistance (thoracic impedance) to determine if a patient has volume overload (or heart failure exacerbation). This can help their cardiologist adjust fluid medication (ie diuretics or “water pills”). Medtronic was the first to offer this feature, and still has the most robust thoracic impedance monitoring compared to other device manufacturers who now also offer this feature.