Evolution of Technology

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.

Evolution of Procedure

Transvenous Defibrillators

Defibrillators are implanted for prevention of sudden cardiac death. They are different from pacemakers since pacemakers only speed up slow heart rates while defibrillators can deliver high-energy shocks to reset or re-start the heart during dangerous heart rhythm disturbances. Essentially, they perform a similar task to the paddles that an EMT would use on the field but do this automatically and within seconds of a life-threatening episode. There are two varieties of defibrillators: subcutaneous and transvenous. The transvenous type is much more common.

Transvenous defibrillators are implanted on the chest wall through a small incision (approximately 5 cm) followed by accessing the axillary, cephalic, or subclavian vein. The wire is inserted through the vein into the heart. This is attached to the defibrillator generator, the generator is placed under the skin, and the skin is closed with sutures. All transvenous defibrillators also have the ability to act as a pacemaker.

Subcutaneous defibrillators are implanted on the chest wall, but closer to the axilla (armpit) region through a 5 to 10 cm incision. An additional incision is made along the sternum (middle of the chest) where a wire is snaked under the skin (not in the vein). The wire is attached to the defibrillator generator, the generator is placed under the skin, and the skin is closed with sutures.

Evolution of Diagnosis

Ventricular Tachycardia (Sudden Cardiac Death)

Sudden cardiac death is most commonly secondary to heart rhythm disturbances (ventricular tachycardia and ventricular fibrillation). We all have some small amount of risk of sudden cardiac death, but those with some genetic and some acquired disorders are at significantly higher risk. Genetic disorders include long QT syndrome, Brugada syndrome, and arrhythmogenic right ventricular dysplasia. Acquired conditions that predispose to sudden cardiac death are typically varieties of cardiomyopathies: nonischemic cardiomyopathy, viral cardiomyopathy, and ischemic cardiomyopathy. Additionally, anyone who has had a sudden cardiac death event and was resuscitated is at high risk for subsequent events.