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  Types of Pacemakers and their Complications By DoRIs J. W. EsCHER, M.D. T E THREE TYPES of artificial cardiac pacemaker systems in common clinical use are: 1. Implantable pulse generators with endo- cardial or myocardial electrodes for long-term or permanent use. 2. External, miniaturized, transistorized, patient-portable, battery-powered, pulse generators with exteriorizedelectrodes for temporary transvenous endocardial or transthoracic myocardial pacing. 3. Console battery- or AC-powered cardiovertors, defibrillators, or monitors withhigh-current external transcutaneous or low-current endocardial or myo- cardial circuits for temporary pacing in asynchro- nous or demand modes, with manual or triggered initiation of pacing. Console Pacemakers The simplest and fastest method of pacing is external transcutaneous stimulation by two elec- trode plates or subcutaneous needles applied to the skinof the chest.1 However, the high voltages required (75-150 v) to penetrate to theheart result in vigorous and painful contractions of the muscles of thechest wall,tolerable onlyunder sedation. Capture is uncertain ill the obese or emphysema- tous patient, and skin burns may occur as a result of insufficient electrode jelly or prolonged use. This route of pacing, therefore, is reserved for brief emergencies or where no other means are available. The use ofalternating current (AC) powered consoles for temporary endocardial or myocardial stimulation always carries the risk of malfunctionwith the possibility, despitesafeguards, of inducing ventricular fibrillation by AC leakage into the pacing wires.2 Battery-powered consoleseliminate this direct risk, but as pacemakers they are bulky, limit mobility and ambulation, and are less convenient and more expensive thanminiaturized units. External Pacemakers External, patient portable, battery-powered pulse generators are designed to provide a wide range of choices in pacing rate, current amplitude, and mode of action. Several models are available (table 1). Common features are that they are small in size (average 11.7 x 7.4 x 3.1 cm), are light in weight (average 3.0 g), can be strapped to the patient's chest or limbs, are designed toaccept, directly or by adapters, all or almost all electrodes likely to be utilized with them, are readily serviced for battery changes or cleaning, are capable of gas autoclaving for sterilization or contamination control, and are ofincreasingly dependable reliability. These units operate in the asynchronous and R- wave inhibited modes over a wide range of rates. Their low trigger sensitivity may allow fortheir use in atrial as well as ventricular noncompetitivepacing. The Vitatron Triplextern offers the addi- tional feature ofventricular synchronous pacing. This has a very useful special application in treatment of pacing failureof an implanted system operating in the fixed-rate mode with intermittent stimulus output or with regular output but intermit- tent capture. In these cases, where the implant emission cannot be suppressed by external stimuli and induces competition with asynchronous exter- nal pacing or suppression of R-wave inhibitedexternal pacing, synchronous pacing locks to the timing of the implant emission and effects noncom- petitive external supplemental pacing. It is not preferable to ventricular-inhibited pacing in routine use,as the stimulus artifact in the absolute refractory period deforms the electrocardiogram and may not be absolutely safe.3 The Triplextern also has a six-beat hysteresis in the R-wave inhibited node. The optional rate-doubler feature of the General Electric External Standby is useful in the special case of rapid supraventricular tachyeardias where it permits capture and rate reduction by overridingpacing or the disruption of a rapid tachycardia or flutter by the blocking action of brief application of very high rates.4' 5 Rapid fixed rate pacing (to 400 beats/min), atrial and ventricular synchronous or stimulus-inhibited pacing, and paired and coupled pacing are otherwise available only in specialized instruments, such as Medtronic Multiple Mode ResearchGenerator(5837) or the CordisSyn- chrocor II. 1119 From the Cardiology Service Medical Division, Montefiore Hospital and Medical Center and the Albert Einstein College of Medicine, Bronx, New York. Circulation, Volume XLVII, May 1973   b  y g u e  s  t   onF  e  b r  u a r  y1  0  ,2  0 1  7 h  t   t   p :  /   /   c i  r  c  . a h  a  j   o ur n a l   s  . or  g /  D o wnl   o a  d  e  d f  r  om   C : ? Cl X Cl 0 CS 0 0 LI, - 0 c CC Co 0 W C 0 tc et , c3 . _ s c, 0 ._._._ r.2 Z1 CQ) 55 c Ct c3 -4 .C S C-) 0 -C - ClCl 0 G 0C cl- 0 cl 6 0 Cl 6 N ._1- N 0 r C c3 Cl 0  41 Cl CD Ct 0 ol C*U 41 a o CO>- o-- Cs < o C- C.) 0t cl] 6 00 cc - 0 C 4o ¢~ ~ ,r, C -> > Circulation, Volume XLVlI, May 1973 1120 ESCHER W CC5 . -C , cl, (4 ,- W ° m c3 ;.  sH C)W -Q. v> Cl Cl Cl '   j_ O-- -4i d CC C W) 0 C c 0 q) C4 C a2 C C C-fl ,- D P._ CC to .;F V-/ a- a) C: c Cl 0   C^ C; CC N CC M.4 Q pc CO E-( C-C~ C.. C3 Ce C-. P-.) c C X -. PC IS.- Cl C) 0 0 I) DC c 0 oe i C.) C -4-- F-- 0 0 C) 0 c C0 U U mX C) 0 UU 0 4-f~ C.) ._ W S   b  y g u e  s  t   onF  e  b r  u a r  y1  0  ,2  0 1  7 h  t   t   p :  /   /   c i  r  c  . a h  a  j   o ur n a l   s  . or  g /  D o wnl   o a  d  e  d f  r  om   TYPES OF PACEMAKERS Any unipolar or bipolar temporary or implantable pacemaker electrode can be connected to any of these externalgenerators. The routes and technics of application and their special utilities or problems are: (1) Percutaneous transthoracic direct myocar- dial puncture of the left ventricle by a needle electrode or by a temporaryneedle inserter through which a fine-wire or coil-spring electrode is passed to the lumen.6 This technic, reserved for the acute emergency,can be lifesaving. Complications are potentially grave and include the possibility of pneumothorax, damage to a coronary artery, tam- ponade, and, especially if used during closed-chest massage, of unstable pacing or electrodedisplace- ment. (2) Myocardial wires inserted by thoracotomy after pulmonary or cardiac surgery6' 7 In this application, anexposedsegment of an otherwise insulated 0 or 00 braided-steel wire suture is stitched through the myocardium in such a fashion that a light tug can remove it without difficulty. Two wires are applied to the chamber to be paced (atrium or ventricle) for bipolar pacing. In unipolar pacing, one wire (the cathode) is applied to the myocardium,and the second  indifferent wire (anode) is applied to the skin. Common difficulties are prematuredisplacement of the loosely applied wires and/or marked increases in threshold to pace. Less frequently, failure to pace is caused by touching of exposed wires or their approximation influid pools, with short circuit of output or demand suppression of output by ectopic (wire motion or interference) signals. If the signals are rapid transients, they may not be seen on theperipheral electrocardiogram or even on the myo- cardial electrogram but should appear on an oscilliscope withan expanded time and amplitude scale.8 (3) Percutaneoustransvenous endocardial cathe- ter electrodes passed to the rightventricleorright atrium though theright or left subclavian vein by the infra- or supraclavicular route and the right or left femoral. brachial, and external or internal jugular veins.9' 10 The electrodes commonly used are the United States Catheter and InstrumentCorpo- ration (5651, 5652) and the Electro-Catheter Company (Elecath 0501-2, 3501-2) 5F and 6F bipolar catheter electrodes, usually passed under direct observation by fluoroscopy, and the CordisCorporation (370-110) and Elecath (561) semi- floating 4F bipolar electrodes, usually passed by indirect electrocardiographic control. The heavier Circulation, Volume XLVII, May 1973 and stiffer electrodes are more likelyto stay in place if they are positioned visually as well as electrically. They are inserted in thejugular and brachialveins by direct cutdown, and similarlyin the femoral veinsof children. In adults, they are passed routinely by percutaneous needle in the femoral vein and occasionally in all other veins. The semifloating electrodes are almost always inserted by percutaneous needle, usually by the subelavian or brachial veins, and occasionally by any other vein. They can be monitored by electrocardiograph or X-ray. A number of complications relatespecifically to particularsof application. The brachial route is associated withan increased incidence of thrombo- phlebitis'1 and of motion displacement12 of any electrode (especially if the arm is lifted over shoulder level) with disruption of pacing'3 and myocardial perforation.14 To a lesser degree, motion displacement occurs with the femoral route when both knee and hip are flexed90', but disruptionof pacing is much less frequent (5-7 ) and accidentalperforation of the artery during insertion (3%) responds promptly and benignly to 5 min of local pressure.9 15 The subelavian route is known to allow arterial puncture (3%), pneumothorax (0.7%), and rarely an extravascular,intrapleural electrode passage. The relatively high freouency ofeasilv corrected elec- trode malposition (17 ) is not a function of route but of positioning by electrocardiography rather than by direct vision. Bacteremia (1%) and gross sinus infection (2 ) are problems common to all percutaneous insertions but fortunately of low incidence, especially with good skin hygiene, and are promptly responsive to electrode withdrawal and antibiotic therapy.16 Most of the operating complications are inherent in the situation: theexternal electrodes are temporarilyconnected; the pulse generators are subject to disruption and interference because they are exposed and mobile, with adjustable controls and short-life removable batteries; they are han- dled, mishandled, and serviced by various person- nel or even patients. Because they are exposed, however, theycan be inspected, tested, repaired, or changed with notrauma to the patient unless an electrode has to be repositioned or replaced. The major problems are an increased incidence of external damage, wetting, wire shorting, poor extermal electrode contact, gross electrode displace- ment orinternal electrode malposition, battery 1121   b  y g u e  s  t   onF  e  b r  u a r  y1  0  ,2  0 1  7 h  t   t   p :  /   /   c i  r  c  . a h  a  j   o ur n a l   s  . or  g /  D o wnl   o a  d  e  d f  r  om   ESCHER depletion, and theincreased risk of AC interference or induced fibrillation.2' 8 Implanted PacemakersImplantedpacemakers areof two basic types: (1) fully implanted; (2) radiofrequency orelectro- magnetically coupled semiimplants. In the semiimplanted group, thepulse generator, with replaceable batteries and variable rate and current-amplitude controls, is carried externally. Its pacing stimulus is released through a primary-coil antennataped to the patient'sskin overlying an implanted secondary-coil receiver. The implanted unit is a subcutaneous secondary coil attached to a standard implantable myocardial or endocardial electrode.17-21 Surgery is not required for pulsegenerator replacement, and many threshold or rhythm problems can be handled by changes of rate or current amplitude or the use ofspecially tailored pulse generators.22 The very small size ofthereceiving capsule can be accommodated in the limited subcutaneous tissue of infantsor cachectic adults eliminating the tumescence and pressurenecrosis that can result in these patients even with  pediatric -sized fully implantable pulse genera- tors. The disadvantages are thebulk, constant presence, and psychological pressure of the need to care for the external generator and relativelyfragile antennae, the risk of accidental displacement or fracture of the antennae (intrinsic tothis system), and the fact that these systemsoperate only in thefixed-rate mode. In the United States the relatively carefree fully implanted pacemakers are preferred, and thereforethe semiimplanted systems are very rarely used. Only one, the Cordis Corporation Transicor, is available by special order. In Europe, especially England, they are in more prevalent use, even where competition could be anticipated because of theirfixed-rate limitation.23-25 Fully implantedpacemakers are now manufac- tured in most nations with sophisticatedtechnol- ogies. Tables 2 and 3 list most instruments made orretailed in the United States. Established producers and new firms (e.g., in the U.S.A., Edwards Laboratories) regularly introduce new models. Fully implanted pacemakers are categorizedprimarily on the basisof their pulse-generator function as asynchronous, atrial synchronous, ven- tricular synchronous, and ventricular inhibited. The latterthree, with sensing circuits, are also known as triggered pacemakers. The ventricular synchronous and ventricularinhibited units, variously termed demand or standbypacemakers, are both noncom- petitive instruments. Implanted pacemakers are further cross categorized by whether they are unipolar or bipolar, transvenous endocardial or transthoracic myocardial systems and whether they are pacing the ventricle or the atrium. Asynchronous Pacemakers These are defined as  pulse generators in which the repetition rate is independent of the electrical and/or mechanical activity of the heart. 26 Their stimulus repetition rate usually is setat 60-70 beats/min for adults and 80-100 beats/min for children, and they discharge at thisrate regardless of the underlying rate or rhythm of the patient. They have the simplest construction and are the most stable and long lasting of all implants. Without a current-utilizing, continuously operating sensing circuit they havefewer components to fail, no nonpacing battery drain,27 28 and little or no response to electromagnetic interference.29 They even have a somewhat lower incidence of problems with their electrodes, because they exclude thoserelated to failure to sense or to the delivery of false signals as may occur in triggered systems.27 The major defect of asynchronous pacing is competition if there are interpolated spontaneous beats or tachyarrhythmias. Patientsoften find theresultant  palpitations disquieting. Physician dis- quiet foresees competition-induced ventricular fibrillation. The degree of risk of this occurring is disputed but is probablylow in healthy patients and increases if there is tissue anoxia or injury, electrolyte imbalance, or drug toxicity.30-32 Atrial Synchronous Pacemaker Historically the first implantable triggered sys- tem,33 it is  aventricular stimulating pulsegenera- tor, therepetition rate of which is directly determined by the atrial rate 26 (table3). It senses the atrial contraction voltage and,following a simulated P-R interval, emitsaventricular stimulus. It utilizes two electrodes, atrial sensing and ventricular stimulating. These are usually sutured to the left atrium and ventricle, when implantation is by thoracotomy. The atrial potential to the sensor is 3.0-8.0 mv.34 Right-sided transvenous atrial synchro- nous pacing is much less reliableas atrial electrode stability is difficult to maintain and the atrial signal is only 0.5-3.0 mv.34 35 If the atrial signal is lost, becomes subthreshold, or slows below the base rate (lower escape rate), these pacemakers are pro- gramed to drop into asynchronous pacing at 60-70 beats/min foradults, 70-90 for children. An upper Circulation, VolumeXLVII, May 1973 1122   b  y g u e  s  t   onF  e  b r  u a r  y1  0  ,2  0 1  7 h  t   t   p :  /   /   c i  r  c  . a h  a  j   o ur n a l   s  . or  g /  D o wnl   o a  d  e  d f  r  om 
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