Implantable Therapies

Advances in microtechnologies have now made it possible to create implantable therapies that can be lifesaving, such as implantable defibrillators, which have detected and treated thousands of episodes of sudden cardiac fibrillation. As mentioned, the potential for large numbers of such devices will likely increase at an exponential rate and will be directed specifically to all types of cardiac complications.

3.1. Left Atrial Appendage/Atrial Fibrillation Therapy

There are growing numbers of treatments for the side effects of atrial fibrillation that, in some patients, lead to crippling strokes. The focus of these devices is to modify the role of the left atrial appendage in pathologies associated with atrial fibrillation. More specifically, this tiny alcove of the heart, which has been described to serve as a "starter heart" for the human embryo, can be a site for blood to pool and subsequently form clots that can be expelled into the brain, causing strokes. Today, it is estimated that atrial fibrillation affects 5 million people worldwide and is thought to be responsible for up to 25% of all strokes.

At present, the most common treatment for atrial fibrillation is the administration of a strong anticoagulant drug called coumadin. From a device perspective, suggested approaches to treat this problem include tissue clamps, screens, and other methods to seal off the appendage. More specifically, one startup company, Atritech Inc. (Plymouth, MN), has promoted a solution to implant a tiny filter into the appendage, letting blood pass through, but trapping clots inside the minichamber; after some time, the body would naturally seals the chamber.

3.2. Cardiac Remodeling

Chronic cardiac remodeling is a well-known response of dilated cardiomyopathy and is thought to play a central role in disease progression (12-14). Associated heart chamber dilation or wall thinning will elevate overall wall stress, which is considered to trigger the local release of neurohormones, which adversely affects myocardial molecular biology and physiology (15). Therapeutic approaches to treat heart failure have been described, primarily as a means to inhibit or even induce reverse remodeling (e.g., p-adrenergic blockade).

Mechanical unloading using left ventricular assist devices (LVADs; see Chapter 30) or extracorporeal pumps (Fig. 4) have been employed as alternatives. Such interventions can profoundly unload a heart, leading to reverse remodeling and improved physiological performance (12).

Another approach for accomplishing this benefit is to induce structural remodeling by imposing alteration on or within the heart. For example, the CorCap™ Cardiac Support

Device (Acorn Cardiovascular Inc.™, St. Paul, MN) is a fabric mesh multifilament implant that is surgically positioned around the ventricles of the heart (Fig. 5). This product is designed to reduce ventricular wall stress by supporting the heart muscle. Preclinical studies have shown that supporting the heart in this manner stops deterioration and allows the muscle to heal or remodel (14). More specifically, the deployment of this device is expected to improve the heart's ability to pump blood, provide relief of heart failure symptoms, improve quality of life, and ultimately extend survival for those who suffer from heart failure. Since April 1999, more than 270 implantations of the CorCap™ Cardiac Support Device have been performed worldwide; the devices are currently being evaluated through randomized clinical trials in North America and Europe.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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