1 Basic structure and function of buried cardioverter defibrillator (ICD)
The ICD consists of a pulse generator and an electrode lead. The main components of the pulse generator include the battery, the sensing and pacing lines, and the capacitor. The battery supplies energy. The function of the capacitor is charging and discharging. The sensing and pacing lines are responsible for ECG monitoring, recognition of ventricular tachycardia (VT), ventricular fibrillation (VF) and bradycardia, and pacing pulses. The early electrodes were epicardial electrodes, which were opened for thoracic surgery and later improved to subcutaneous electrodes. Now progressing to the transvenous endocardial electrodes, the burial technique is greatly simplified. The electrode lead transmits the sensed signal to the pulse generator on the one hand and transmits the pacing signal to the heart. Due to the different electrode types, the shock can be accomplished by the transvenous electrode and the housing of the pulse generator, or by the transvenous endocardial electrode itself.
The basic function of the ICD is to identify and deal with tachyarrhythmia and bradycardia, and its recognition and treatment of bradycardia works in the same way as anticardiac pacemakers. Only the principles for identifying and dealing with tachyarrhythmia are described here.
1.1 Identification of rapid arrhythmia
The heart rate (or its corresponding perimeter) and duration (or the number of cycles of tachyarrhythmia) with a rapid arrhythmia are used as the basic recognition criteria, which have initial recognition and re-identification. The initial recognition criteria are used for each burst. The first judgment of arrhythmia episodes, the re-identification criteria for the determination of tachyarrhythmias that were not terminated by ICD therapy. VT and VF are mainly distinguished by frequency. Different manufacturers have different representations of the above identification criteria. For example, CPI companies directly express the frequency (time/minute) and duration (s), while Medtronic replaces the frequency with the perimeter and continues with the number of cardiac cycles. time. The following examples illustrate how ICD recognizes tachyarrhythmia.
If the VT recognition criteria is set to 150 beats/min, and I hope that the VT episode lasts 10 s, the ICD begins treatment. If the ICD used is CPI's Ventak PRx III, the frequency standard can be set directly to 150 beats/min and the duration is set to 6 s, since the duration calculation is started after the frequency standard is met. The ICD's process of continuously monitoring heart rate is the process of comparing the circumference of each heart to the perimeter of the frequency identification criteria. When ICD is judged in 10 consecutive heart circumferences, 8 is equal to or shorter than the set perimeter of the identification criteria. When the frequency standard is 150 beats/min and the circumference is 400 ms, the ICD is determined to meet the VT diagnostic criteria and start calculating the duration. Obviously, before the calculation of the duration, the tachycardia has lasted for at least 10 cardiac cycles. With the above 150 times/divided identification criteria, the 10 cardiac cycles should be 4 s, so the duration is set to 6 s and the VT is actually Lasted 10 (4+6) s. After starting the calculation of the duration, if there are always 6 of the 10 cardiac cycles that meet the frequency identification criteria and remain until the end of the set duration (6 s as exemplified above), the treatment procedure begins at the end of the duration. Otherwise, it is necessary to re-satisfy 8 of the 10 consecutive cardiac cycles to meet the frequency standard before starting the calculation of the duration. In the same situation, if you use Medtronic's Jewel series, you need to set the frequency standard to 400 ms and the duration to 24 cardiac cycles (25 cardiac cycles should be 10 seconds, but there is no 25 in the programmable parameters) If the 24 cardiac cycles continuously meet the recognition criteria, the treatment procedure begins. The frequency standard and duration of such an ICD are simultaneously met, that is, the starting point for the calculation of its duration is different from that of CPI. The setting of the VF duration is also exemplified. If the VF frequency standard is set to 200 beats/min, and it is expected to start treatment for 6 s, the CPI product setting method is the same as VT, that is, the frequency is 200 beats/min, and the duration is 3 s (due to the 10 cardiac cycles occupied time is 3 s); Medtronic's products require a frequency standard of 300 ms and a duration of 15/20. The latter meaning is that 15 of the 20 consecutive cardiac cycles (lasting 6 s) can meet the set frequency standard perimeter, that is, the diagnosis of the diagnostic strip VF is only the standard of heart rate and duration, and the diagnosis of VT is in addition to the above. In addition to the basic criteria, there are additional criteria to choose from in order to differentiate from sinus tachycardia and atrial fibrillation. Commonly used people have a sudden onset of rapid arrhythmia (Onset is insufficient.
The diagnosis of VF is only the standard of heart rate and duration. In addition to the above basic criteria, VT diagnosis is also available as an auxiliary standard for differentiation from sinus tachycardia and atrial fibrillation. Commonly used have sudden onset and stability of rapid arrhythmia, and some ICDs have added QRS group wave width to identify VT and supraventricular tachycardia (SVT).
Suddenness refers to the degree to which the interval between tachycardia and sinus rhythm is shortened, usually expressed as a percentage. VT is sudden and sudden, and sinus tachycardia usually occurs gradually and gradually. Therefore, both can be identified using burst criteria. The specific setting of suddenness is determined according to the law of the interval of the tachycardia when the patient has tachycardia. For example, if the interval between the tachycardia is 25% shorter than the circumference of the sinus heart rate, the burstiness can be set to 20%. . Once the suddenness is selected, the heart rate, duration, and suddenness of the initial recognition criteria must meet the diagnostic conditions of VT.
Stability refers to the maximum allowable range of differences between different circumferences of tachycardia, that is, the regularity of the heart rhythm during tachycardia, usually expressed in milliseconds. Atrial fibrillation also has a rapid ventricular rate, but the heart rhythm is irregular, while VT is rhythmical or only slightly irregular. Therefore, the two can be identified for stability. If we observe that the difference between each circumference of the previous VT is less than 30 ms, the stability can be set to 40 to 50 ms. After selecting the stability standard, the heart rate, duration and stability of the initial recognition standard must be met to meet the diagnostic conditions of VT. Patients with SVT can be identified by the QRS complex width standard.
1.2 Treatment of rapid arrhythmia
The treatment of rapid arrhythmia has two methods: shock and anti-tachycardia pacing (ATP).
(1) Electric shock: At present, the electric shock energy of most products can be controlled from 0.1 to 34 J. The product models are different, the specific parameter settings are different, the maximum electric shock energy of a few products can reach 42 j, and most products can be shocked 6 times in a row. Both VF and VT can be used this way.
(2) ATP: There are two basic forms, namely, short phasing bursing and grading grading (Ramp pacing).
1 Short-array rapid pacing refers to the pacing mode in which the circumference is equal and shorter than the circumference of the tachycardia in the same pacing. The setting of the pacing circumference is often expressed as a percentage of the tachycardia circumference. Usually, 75% to 80% of the circumference of the cardiac cycle is used as the set value, and the success rate of terminating the tachycardia is high. The number of pulses per pacing is determined by the treatment effect. The number of pacing pulses is too small to be successful, too much is unnecessary, or even accelerates the arrhythmia.
The 2-week descending pacing refers to the pacing mode in which the circumference is gradually shortened in the same pacing. This method of ending tachycardia has a higher success rate than short-term rapid pacing, but there are many opportunities to accelerate arrhythmia, especially when the number of pacing pulses is large.
The treatment of VF can only be done by electric shock. In general, the energy of the first shock is 5 to 10 j higher than the measured defibrillation threshold, and the maximum energy should be used from the second. The treatment of VT can be done in two ways: ATP and electric shock. The electric shock energy can be selected from 0.1 to 34 j, and generally lower energy can be effective. ATP can set up multiple programs, and each of the two pacing modes can be selected and scanned. The so-called scanning means that when an ATP is invalid, the pacing circumference or (and) joint interval of the next ATP can be automatically shortened according to the set value. Therefore, the treatment of VT can adopt the preferred ATP, the low-energy electric shock cardioversion when it is invalid, and the high-energy electric shock cardioversion step treatment when it is invalid.
In addition, ICD has the function of storing intracardiac electrocardiogram and information on the time, circumference, interphase, treatment time, mode and post-treatment response of tachycardia for follow-up and reasonable adjustment of diagnosis and treatment procedures. use.
ICDs have electrophysiological examinations. With this function, tachycardia can be induced and the effect of the treatment procedure can be tested.
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