Problems with Pacemakers

Coagulation is not the only problem with materials intended for implantation, however. Cardiac pacemakers are intended to correct arrhythmias. Insulating materials for a pacemaker lead must be tough and long lasting. The first leads were insulated with polyethylene or silicone rubber. Neither material was considered ideal because of endocardial reactions (polyethylene) and limited durability (silicone rubber). The strength and flexibility of polyurethanes led to their introduction in 1978 as lead insulators. 

Pacemakers are among the most reliable electronic devices ever built device survival probabilities of 99.9% (excluding normal battery depletion) at 10 years are not unheard of. But despite intensive quality assurance efforts by manufacturers, the devices do remain subject to occasional failures the annual pacemaker replacement rate due to generator malfunction has been estimated at roughly one per 1000 devices implanted, a marked improvement in reliability since the early 1980s (Maisel et al. 2006 Maisel 2006). There have been multiple major advisories and recalls issued by the FDA regarding pacing leads, with more of these because of problems with the lead insulation than with the lead conductor. 

Many biomedical devices work inside the human body. Pacemakers, artificial heart valves, stents, and even artihcial hearts are some of the bionic devices correcting problems with the cardiovascular system. Pacemakers generate electric signals that improve abnormal heart rates and abnormal heart rhythms. When pulse generators located in the pacemakers sense an abnormal heart rate or rhythm, they produce shocks to restore the normal rate. Stents are inserted into an artery to widen it and open clogged blood vessels. Stents and pacemakers are examples of specialized bionic devices made up of bionic materials compatible with human structure and function. 

Cardiac arrhythmias are very complex to treat because of multiple causes and because of problems with the treatments available. Medications for this condition have many side effects, some quite serious, and the medications and pacemak-... 

Lewis also cites investigations of problems with synthetic heart valves and implanted pacemaker leads, including mechanical inadequacy, cure variations and biodegradation. Such medical products are subject to apparently exhaustive testing but despite the precautions taken failures have still occurred. 

Muscles, bone, and tendons in the human body are examples of natural organic materials that exhibit piezoelectric effects. For example, one of the authors (Gerdeen) has a medical defect called super ventricular tacardia (SVT), wherein an electric short between the left ventricular chamber and the sinus node in the heart causes au irregular heartbeat. He takes medicine to block this short. Some people have the opposite problem. They have artificial pacemakers installed with electrodes contacting the heart muscles to regulate the heart rate. Normally the human body regulates the heart beats with its own pacemaker when it is in a healthy condition. 

Safety considerations for magnetic resonance (mr) experiments have received Htde attention except for the problems associated with the use of electronic devices such as pacemakers in the magnetic field. However, in a 1990 study of reproductive health involving more than 1900 women working in clinical mr facihties in the United States no substantial differences were reported between the group of women directly involved with mr equipment (280 individuals) and other working women (894 individuals) (10). Conclusions are restricted to exposure to the static external field. 

While it would be difficult to enumerate all of the efforts in the area of implants where plastics are involved, some of the significant ones are (1) the implanted pacemaker, (2) the surgical prosthesis devices to replace lost limbs, (3) the use of plastic tubing to support damaged blood vessels, and (4) the work with the portable artificial kidney. The kidney application illustrates an area where more than the mechanical characteristics of the plastics are used. The kidney machine consists of large areas of a semi-permeable membrane, a cellulosic material in some machines, where the kidney toxins are removed from the body fluids by dialysis based on the semi-permeable characteristics of the plastic membrane. A number of other plastics are continually under study for use in this area, but the basic unit is a device to circulate the body fluid through the dialysis device to separate toxic substances from the blood. The mechanical aspects of the problem are minor but do involve supports for the large amount of membrane required. 

To correct problems of rhythm disturbance or SA node malfunction, cardiologists often use a pacemaker, an electrical device implanted in the shoulder or abdomen of the patierrt with a wire leadir to the heart. This mecharrical pacemaker generates the electrical signal which regulates the heart s functions. The rate of heartbeat, which is set when the pacemaker is implanted, can be changed if necessary without surgery. Modem... 

The evolution of the management of transvenous leads has been born out of the furnace of clinical care and the pathophysiology of lead dysfunction. Transvenous lead extraction is only one tool in the management tool chest. At first it wasn t much of a tool, just a rag tag group of ideas used by a few people trying to solve problems for patients without a solution. However, over the last 25 years and particularly with the visionary efforts of Dr. Charles Byrd and his creative collaboration with Cook Pacemaker Inc. (now Cook Vascular Inc.), transvenous lead extraction is not only a tool but an armory of techniques. 

The use of electrosurgery on patients with metallic implants or cardiac pacemakers may pose problems. Metallic implants are usually considered not to be a problem if the form is round and not pointed, Etter et al. (1947). The pacemaker electrode tip is a small area electrode, where relative small currents may coagulate endocardial tissue. The pacemaker catheter positioning should therefore not be parallel with the electrosurgery current density lines. This is illustrated in Figure 10.22 for a heart pacemaker implant. 

In vivo applications of bioelectronic devices, such as artificial limbs, cochlear or retina implants, will not be stressed here in detail. Many of the problems thathave to be solved for in vitro devices, such as a stable neuron/electrode contact, do also matter for in vivo applications. However, for the latter, much more difficult requirements have to be met, such as biocompatibility not only against the neural cells but the whole body, including resistance to body reactions against the foreign device such as inflammation or scar formation, mechanical stabiHty in a moving system (muscle, eye,...), long-term stabitity over years, as well as practical requirements such as easy implantation. Despite all these difficulties, there are systems such as pacemakers and cochlear implants already on the market [37]. Retina implants are under development [38]. And first studies are made with intelligent artificial limbs. Therefore one can hope that in the twenty-first century many of the above-mentioned problems will be solved. 

Air embolism is a complication associated with the use of the Seldinger technique with a percutaneous sheath set. Air embolism is a well-known, well-documented complication of the percutaneous approach. To avoid this problem, it has been recommended that the patient be well hydrated and placed in the Trendelenburg position. The most important step in prevention is awareness on the part of the implanting physician for the risk of air embolization. There are many steps that may be taken to avoid this complication (Table 4.21) (192). The time of greatest risk is when the dilator is removed from the sheath set. In patients with a volume-overload state, there is little or no risk. On the other hand, an elderly dehydrated patient who has been NPO for many hours is at risk for serious air embolization. It is reconunended that prior to any percutaneous pacemaker or ICD procedure, the patient be maintained in a mild state of overhydration. The patient s state of hydration should be assessed just prior to removal of the dilator. 

Pacemaker pocket erosion continues to be a problem (Fig. 4.104). This is best avoided by creating a pacemaker pocket that has maximum optimal tissue thickness. Occasionally, in extremely asthenic individuals, subpectorahs major muscle pulse generator placement should be considered to afford optimal tissue thickness. Patients can also present with preerosion secondary to pressure necrosis of the overlying tissue. Such situations represent a quasiemergency if one is to avoid complete erosion and wound infection. The patient should be reoperated, the old pocket abandoned, and new pacemaker pocket created away from the involved site. Sutton and Bourgeois incidence of pacemaker pocket complications are shown in Table 4.25 (17). 

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