Tài liệu Principles of pacemaker—myocardial interaction doc

Authors: Moses, H. Weston; Mullin, James C. Title: A Practical Guide to Cardiac Pacing, 6th Edition   !!"#$%&' 3 Principles of Pacemaker—Myocardial Interaction Permanent Pacemaker–Myocardial Interaction (&&)&&* +&*), !-. .(/0&& /&&/ +(,-(/ /&/&/(0//1,,0 &20&/(,()&& &&)&,!)/ )(&)&/&)/) (&)&,-(/ /,//&0*-1 (3, 42+0-(, /&0-&&0&"#5 *"#6 /& &"#$0-& "#5"#6()&), -*&/ ,)*(&/ (,7//0/) &/ !,88 &0//&*//&& &/&9/,&& /&+()0*& /&1&/&&2/ -(/, 3/ 4!-.&7 !, 70:;70)& &//,;:&,< 0 -&0&/&/& &(//& 1&2(,=;>&0-&/ &/1 2*&/, 7&/&0&0& ,&0//&(( ),'(&0(/&+0& (/(,'&&0 ()0-0(, '0&/)/ /&+/&(0// -/,! &&) *& !,8? 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A&)+ 0 ),  /(/&&/& *,(/* /*4?A+//& &&,: &)&(0/ -9&, =& &&//I/&/& /,L)&0/&& *, A&/& A&/&/&, (&(&/&&) -)& ) !,8M (/,7/(&1///(& /&0/,8,<20& /)&B,)// 0&/&&(//1,,0/)( /2,()/)& )/(&,//&& &,(-;/)&/ &/)&/&& ,/0&)//&, '&&0)&/&/&& &/&/&,:/ (&)0)&//,  4)//&/12& &&)/,J*//& )&(*&&( 1/&&/2, TABLE 3-1 Threshold and sensing values for initial implant and generator change a I. Acute measurements (measured at a pulse width of 0.5 msec) 7,& 4, A;N4,A&N ,?A1&& 4,A2 , /;N4,?7 , '&;*8"#@4O :,F 4, .();?A12 , !();,&,?"#@,A II. Chronic measurements (measured at a pulse width of 0.5 msec) 7,& 4, A;N,A , /;N<7 3. '&;//4DE1&)(0// +&)0/&/2 :,F 4, .();8?A , !();4,?0,"#@,A  //&,!(///&)/& &&)&/&&/, !,8K !&/&&&( / &))&&,& /*&0//(&/0  /(4?A) /&)/&& )&,( */&,'&/&7&( 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(/(&&)),3/ <("#@&/ /))/&/(&1 &/&(0&(2,')& /)/(&4,?,&) )&,7/(&/(&/,)&() &0 !,? *&&/&&, 0)/(& *,4,0&/(&,?,7( ,/)(/(& )&,*( , 3/ <F =//), '/0 &//)(&& 1/&2(,7/(&,?0*,8AI/& /,'/(&&4,?0,?AI/& /,>)/)&(/&/, "#5"#6/)/4,?, /&4,?/,)&&&/), *&&(, ''&F &(/&*(0()&( *&/),L&(/(/&& 0((/&9//(&)/,> 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&&&/&/, !,? [...]... resulting in the QRS complex The shape of the QRS complex seen by the cardiac pacemaker has no relation to the shape of the QRS complex as seen on the surface electrocardiogram (ECG) The pacemaker sees an electrogram recorded directly from the endocardium of the heart P wave sensing has become more important with the increased use of dual-chamber pacemakers The P wave, of course, has a lower amplitude and... time of implantation with ST segment elevation B: Chronic electrogram with no ST segment elevation and slightly lower amplitude Any QRS signal can be analyzed as the sum of an infinite number of sine waves A simple example of this concept is shown in Figure 3-10 The geometric figure on the left represents a QRS complex and can be approximated by summing large numbers of sine waves The five largest of. .. Figure 3-11 Amplitude and Slew Rate The amplitude of the electrogram in this example is 10 mV The slew rate of the most rapidly moving portion of the QRS complex (the values shown by the dotted line) is 0.01 V/ 0.01 sec, or 1 V per sec The amplitude of the electrogram is simply the total height (both positive and negative deflection) in millivolts of the QRS complex In general, the greater the amplitude,... characteristics of a steroid-eluting electrode compared with three conventional electrodes Pacing Clin Electrophysiol 1990;13:134 Kruse IM Long-term performance of endocardial leads with steroid-eluting electrodes (Part II) Pacing Clin Electrophysiol 1986;9:1217 Kulakowski P, Malik M, Odemuyiwa O, et al Frequency versus time domain analysis of the signal-averaged electrocardiogram: reproducibility of the spectral... making sensing more difficult Figure 3-9 shows electrograms taken at the time of implantation and approximately 1 year after implantation The initial electrogram (acute) has ST segment elevation (“current of injury”)as a result of localized myocardial trauma where the electrode tip abuts the myocardium Over a period of weeks or months, this acute electrogram becomes a chronic electrogram, with... will be used Slew rate is the rate of change in voltage in an electrogram Mathematically, this is represented by dv/dt Figure 3-11 demonstrates the concept of slew rate and amplitude In general, the greater the slew rate of an electrogram, the more likely it is to be sensed In clinical practice, the slew rate rarely is measured; in fact, simply measuring the amplitude of the sensed QRS complex is almost... of a porous metal mesh (or carbon material) so that the area of metal in contact with the electrolyte solution is large, thereby lowering polarization resistance and increasing the ability of the pacemaker to sense This is shown partly to emphasize the concepts of current density and polarization resistance Temporary Pacing Applications Most of the electrophysiology pertinent to temporary pacing has... high resolution automatic measurements, conversion of pulse width into voltage thresholds PACE 1999;22:567-587 Furman S, Garvey J, Hurzeler P Pulse duration variation and electrode size as factors in pacemaker longevity J Thorac Cardiovasc Surg 1975;69:382 Furman S, Parker B, Escher DJW, et al Endocardial threshold of cardiac response as a function of electrode surface area J Surg Res 1968;8:161 Furman... Figure 3-8 Mechanism of Change in Threshold A: Acute threshold of 0.5 V at implantation The metal electrode tip is in direct contact with the myocardium B: Peak threshold of 3.0 V at 3 weeks Inflammatory cells separate the electrode and the excitable myocardium and disperse the pacing charge before it reaches the myocardium C: Stable chronic threshold of 2.0 V at 6 months A small, stable... complex is likely to be sensed Most pacemaker manufacturers describe the sensitivity of the pacemakers in millivolts (i.e., QRS height) for simplicity New pacing system analyzers can measure slew rate of the sensed electrogram automatically As discussed previously, polarization resistance is decreased if the surface area of the metal in contact with the electrolyte is increased Thus, sensing is better . !!"#$%&' 3 Principles of Pacemaker—Myocardial Interaction Permanent Pacemaker–Myocardial Interaction (&&)&&* +&*), !-. .(/0&& /&&/ +(,-(/ /&/&/(0//1,,0 &20&/(,()&& &&)&,!)/ )(&)&/&)/) (&)&,-(/ /,//&0*-1 (3,. implant and generator change a I. Acute measurements (measured at a pulse width of 0.5 msec) 7,& 4, A;N4,A&N ,?A1&& 4,A2 ,