Development and preliminary clinical tests of an impedance sensing VDD recording pacemaker for diagnosis and research

Episodes of serious but infrequently occurring cardiac arrhythmias can be difficult to detect and analyse, even with modern Holter monitoring. A previous diagnostic pacemaker developed by this group provided VVI pacing therapy and recorded intracardiac ECG signals but had no atrial sensing or impedance measuring capability. A new external diagnostic pacemaker system is described that has been developed to assist in diagnosing intermittent arrhythmias by selectively recording intracardiac signals. Unlike other ambulatory monitors, in addition to recording ECG, the device combines VDD pacing therapy with the capability of monitoring and recording intracardiac impedance and pressure waveforms through a temporary intracardiac lead. A PCMCIA memory card allows storage of 48 arrhythmic events of 21 seconds each. Twelve seconds of waveform are retained before the event occurs and nine seconds after. Data retrieval and processing is performed with a PC which reconstructs each waveform for display. The ECG provides data on cardiac rhythm while cardiac function is inferred from the haemodynamic signals. During simulated trials, 14 event types were presented to the system. All events were successfully detected and recorded. During in vivo clinical tests 83 waveform recordings were made. Impedance fluctuations with typical peak-to-peak values of 64 ohms were successfully recorded.     

Algorithm for ventricular capture verification based on the mechanical evoked response

Automatic pacemaker capture verification is important for maintaining safety and low energy consumption in pacemaker patients. A new algorithm was developed, based on impedance measurement between pacing electrode poles, which reflects the distribution of the conducting medium between the poles and changes with effective contraction. Data acquired during pacemaker implant in 17 subjects were analysed, with intracardiac impedance recorded while pacing was performed in the ventricle at varying energies, resulting in multiple-captured and non-captured beats. The impedance signals of all captured/non-captured beats were analysed using three different algorithms, based on the morphology of the impedance signal. The algorithm decision for each beat was compared with an actual capture or noncapture, as determined from the simultaneous recording of surface ECG. Two of the three algorithms (Z₁ and Z_n) were based on impedance values, and one (Z_n ¹) was based on the first derivative of the impedance. Z₁ was based on a single sample, whereas Z_n ^′ and Z_n ^′ were based on several samples in each beat. The total accuracy for each was Z₁: 43%, Z_n: 87%, Z_n ^′: 92%. It was concluded that impedance-based capture verification is feasible, that a multiple rather than single sample approach for signal classification is both feasible and superior, and that first derivative analysis with multiple samples (Z_n ^′) provides the best results.     

Pacing device therapy in infants and children: a review

The number of pediatric pacemakers implanted is still relatively small. Children requiring pacing therapy have characteristics that are distinct from those of adults, including physical size, somatic growth, and cardiac anomalies. Considering these features, long-term follow-up of pediatric pacemaker implantation is necessary. Selection of appropriate generators, pacing modes, pacing sites, and leads is important. Generally, epicardial leads are commonly used in small infants. On the other hand, the use of endocardial leads in children is increasing worldwide because of their benefits over epicardial leads, such as minimal invasiveness, lower pacing threshold, and longer generator longevity. Endocardial leads are not suitable for patients with intracardiac shunts because of the high risk of systemic thrombosis. Venous occlusion is another significant problem with endocardial leads. With the increase in the number of pacing device implantations, the incidence of infection from such devices is also increasing. Complete device removal is sometimes recommended to treat device infection, but experience in the removal of endocardial leads in children is still scarce. This article gives an overview of pacing therapy in the pediatric population, including discussions on new pacing systems, such as remote monitoring systems, magnetic imaging compliant pacemaker systems, and leadless pacing devices.     

Comparison of several pulse-pressure techniques for monitoring stroke volume

Values of stroke volume calculated from five different formulas utilising parameters derived from the aortic-pressure pulse waveform were compared with stroke-volume values calculated from the thoracic electrical-impedance waveform, which was recorded simultaneously with the aortic-pressure waveform. A total of 195 beats from three closed-chest anaesthetised dogs were compared. During the recording of the impedance and blood-pressure waveforms, the cardiac output was measured by dye and saline dilution. The mean of stroke-volume values from the impedance method was 39% greater than the mean ‘stroke volume’ calculated by dividing the dye cardiac-output value by the mean heartrate measured during the recording of the dye-dilution curve. The correlation between impedance and dye cardiac-output values was 0·879. The correlation of dye ‘stroke volume’ with values calculated by all four formulas was about 0·89. Individual stroke volumes could be markedly affected by variations in the beat-by-beat values of the total systemic resistance.     

ECG telephone transmission for monitoring pacemakers and cardiac arrhythmias.

A network of ECG telephone transmission has been established which uses simple and inexpensive equipment, and which is aimed particularly at arrhythmia monitoring. Hospitals in areas remote from major medical centers are able to transmit to the Toronto General Hospital for expert advice. 400 patients in their homes may transmit to any of these hospitals for monitoring of pacemaker function or intermittent cardiac arrhythmia. Any patients in the Toronto General Hospital not admitted for a cardiac problem may be monitored via telephone by the expert nurses in the coronary care unit if a cardiac arrhythmia should arise. Equipment for the system has been carefully designed to minimize cost and to make it simple to use, particularly for the old or infirm patients in their homes. Transmissions between hospitals meet American Heart Association specifications for ECG recording. Transmissions of arrhythmias from patients' homes are carried out with a reduced low-frequency response. Expert cardiologists find both transmissions acceptable for their particular purpose. Standards should be set for simple, economic transmission systems as well as for those meeting the most stringent criteria.     

心房颤动导管射频消融对心脏起搏器安全性影响的临床研究

目的评价植入起搏器患者经导管射频消融治疗慢性心房颤动(房颤)的安全性。方法18例永久性心脏起搏并房颤患者,其中男性12例,女性6例,年龄55～78岁,平均年龄68.67岁(标准差8.72岁)。分析其接受导管射频消融术中全程记录的心电信息,判断有无感知、起搏功能不良及房室失夺获、噪声反转等现象,并用起搏器程控仪于导管射频消融术前及术后第1天观察房室感知、起搏阈值及电极阻抗等参数的变化。结果18例患者均顺利完成导管射频消融,肺静脉前庭电学隔离率为100%。导管射频消融前后起搏器感知、起搏阈值及阻抗的变化无统计学意义(P>0.05)。导管射频消融过程中,3例(17%)出现噪声反转,3例(17%)出现感知不良,1例(6%)出现起搏功能不良致心室失夺获,均于停止放电后恢复正常。3例(17%)慢性持续性房颤患者在电复律后出现一过性感知不良。结论射频电流和电复律可引起一过性感知、起搏功能的障碍,但一般不引起起搏、感知阈值及电极阻抗的改变。对于已植入心脏起搏器的慢性房颤患者,在需行导管射频消融术时是安全的。     

Clinical evaluation of a wireless ECG sensor system for arrhythmia diagnostic purposes

In a clinical study, a novel wireless electrocardiogram (ECG) recorder has been evaluated with regard to its ability to perform arrhythmia diagnostics. As the ECG recorder will detect a “non-standard” ECG signal, it has been necessary to compare those signals to “standard” ECG recording signals in order to evaluate the arrhythmia detection ability of the new system. Simultaneous recording of ECG signals from both the new wireless ECG recorder and a conventional Holter recorder was compared by two independent cardiology specialists with regard to signal quality for performing arrhythmia diagnosis. In addition, calculated R–R intervals from the two systems were correlated. A total number of 16 patients participated in the study. It can be considered that recorded ECG signals obtained from the wireless ECG system had an acceptable quality for arrhythmia diagnosis. Some of the patients used the wireless sensor while doing physical sport activities, and the quality of the recorded ECG signals made it possible to perform arrhythmia diagnostics even under such conditions. Consequently, this makes possible improvements in correlating arrhythmias to physical activities.     

A demand radiofrequency cardiac pacemaker

An implantable capsule containing circuitry to transmit the endocardial ECG and convert received radio-frequency pulses to constant current stimulus pulses is described. Inasmuch as the control unit of the pacemaker is located outside the body wall, different modes of pacing (self-synchronous,R-wave coupled, and asynchronous) are possible. Alterations in the capsule load impedance, coupled to the transmitting antenna, is the method of transmission. A signal to noise ratio of 10:1, with a 1 mv source ECG signal can be obtained through a 2 cm spacing between the implant and external coil. The endocardial ECG may be recorded and employed to reveal alterations in electrode geometry. The anode electrode is attached directly to the implanted capsule, providing a unit having a single flexible electrode. The assembly allows recording the endocardial ECG without a wire connection to the hospital utility system. Due to the constant current feature, placement of the external coils is less critical than radiofrequency coupled tissue stimulators previously described.     

Transmission and non-transmission portable ECG in home care medicine

Portable electrocardiography is advantageous in that patients can record ECG by themselves at any time and place. Portable ECG can be classified into two kinds of devices, transmission type and non-transmission type. By using transmission-type portable ECG, patients can obtain an ECG diagnosis from the center by transmitting the recorded ECG. Transmission-type portable ECG is extremely useful for patients needing emergency treatment for such as an attack of ischemic heart disease or arrhythmic event. On the other hand, a patient has to go to a specialist to obtain an ECG diagnosis with the non-transmission-type portable ECG device after recording the ECG alone. As this model is slightly cheaper, and is easy to use, the non-transmission-type portable ECG is good in non-emergency use for early diagnosis and prevention of cardiac disease. Portable ECG is useful for ECG monitoring over time without seeing the patient, not only for symptomatic analysis of the patient. For example, silent myocardial ischemia and arrhythmic events developing during exercise will become clear in periodical portable ECG recording. In particularly, portable ECG is useful for noncontinual ECG monitoring of patients with Brugada syndrome and those administered with antiarrhythmic drugs. Portable ECG increases the opportunity to discover cardiac disease from the aspect of preventive medicine. When patients use a portable ECG during exercise, they can understand whether the exercise is suitable for their heart. Portable ECG is a useful measurement in preventive medicine as described above, not only for the home care of patients.     

Design,implementation and evaluation of amicrocomputer-based portable arrhythmia monitor

The design of a portable, battery-operated microcomputer-based monitor for ambulatory ECG recording and analysis is described. Designed for real-time cardiac arrhythmia analysis, it is suitable for use on ambulator, patients for several weeks, and is about the size and weight of a Holter recorder. The device differs from a Holter recorder in that is does not store normal complexes but recognises and alarms on significant arrhythmias. It sotres 16 s of the arrhythmic event, which it can transmit by telephone to a central receiving station for immediate appraisal by a cardiologist. The monitor uses a CMOS microcomputer and has 2kbytes of program memory and 2kbytes of data memory. The arrhythmia monitor program recognises tachycardia, bradycardia, asystole, dropped beats, and PVCs. The alarm limits are physician programmable. The performance of the monitor was evaluated with standard annotated ECG tapes provided by MIT/BIH. This device should be useful for applications such as antiarrhythmic drug studies, for pacemaker and postsurgery evaluations, and for detecting premonitory as well as life-threatening arrhythmias.     

Ergometry and long-term ECG for assessing bradycardiac and tachycardiac heart rhythm disorders in symptomatic patients over 70

The usefulness of exercise testing and long term-ECG recording in old age was evaluated in a retrospective study. During a period of 24 months 317 long-term-ECGs in 195 patients greater than 70 years and 208 exercise tests in patients greater than 70 years were performed. The mean age of the patients was 73 +/- 3 years. Long-term ECG revealed a high incidence of supraventricular arrhythmias, while PVCs were found in only 28.7% of patients and PVCs greater than 30/h in only 7.3% of patients. Complex ventricular arrhythmias occurred in 25% of patients. Long-term ECG recording appeared to be of particular value in detecting abnormal regulation of heart rate and bradycardia, although symptom correlation with arrhythmias recorded was rare. Exercise testing revealed a higher incidence of PVCs with PVCs recorded in 67% of patients and PVCs greater than 2/min in 42% of patients. The incidence of complex ventricular arrhythmias was slightly greater compared to long-term recording with 29% of all patients. Exercise testing was particularly useful in detecting complex arrhythmias in patients with additional signs of myocardial ischemia (ST-segment depression and/or angina pectoris during increasing levels of exercise). Thus comparing both exercise testing and long-term ECG both appeared to be useful methods to uncover arrhythmias in symptomic patients older than 70 years and have to be considered as complementary tools. Exercise testing is particularly useful in recovering complex ventricular arrhythmias in patients with signs of myocardial ischemia during exercise. Long-term ECG on the other hand allows better recognition of bradycardias and conduction defects that may also be present and may contribute to the patients symptoms.     

Successful bridge to resynchronization therapy with a left ventricular assist system in a patient with idiopathic dilated cardiomyopathy

Implantation of a left ventricular assist system (LVAS) in patients with idiopathic dilated cardiomyopathy (DCM) may improve cardiac function and allow explantation of the device. Generally, an ejection fraction of more than 40% is considered necessary for successful weaning from an LVAS, but less than 10% of DCM patients with an LVAS can achieve such a significant recovery of cardiac function. Cardiac resynchronization therapy, or atrial-synchronized biventricular pacing, has been found to treat congestive heart failure and ventricular dyssynchrony effectively. Here we report on a patient with an LVAS, in whom enough functional recovery could be obtained with resynchronization therapy for the device to be explanted successfully. A 32-year-old man was implanted with a Toyobo-NCVC paracorporeal LVAS to treat his intractable heart failure caused by idiopathic dilated cardiomyopathy. While on the LVAS for 8 months, his cardiac function recovered to some extent. The ejection fraction of his left ventricle (LVEF) improved from 9% to 41%. He chose explantation of the device rather than heart transplantation. Because he occasionally showed a wide QRS pattern on his ECG, epicardial biventricular pacing leads as well as a biventricular pacemaker were implanted on LVAS explantation surgery. An echocardiogram 2 weeks after explantation showed a marked difference in his LVEF by switching his biventricular pacing on and off (40% with biventricular pacing on and 29% with it off). Biventricular pacing may help recovery of cardiac function in selected LVAS patients and contribute to the increase in bridge to recovery cases.     

起搏器术后患者常规及动态心电图监测的临床研究

目的 比较常规心电图与动态心电图在起搏器术后监测的效率,探讨分析动态心电图对不同起搏器术后监测的临床价值。方法 选取皖南医学院弋矶山医院心内科2016年5月~2017年12月100例起搏器植入术后患者为研究对象,所有患者均行常规心电图、动态心电图检测,比较常规心电图和动态心电图对起搏器术后功能异常检测效率,并分析动态心电图对不同起搏器感知、起搏功能异常以及起搏相关心律失常情况。结果 对起搏器植入术后患者动态心电图检测搏器功能异常为44例,高于常规心电图检测的16例,差异具有统计学意义（P＜0.05）。DCG对不同类型起搏器感知和起搏功能异常、自身心律失常比较,差异无统计学意义（P＞0.05）。结论 动态心电图对起搏器起搏功能异常的检测效能较12导心电图高,并且可以作为一种无创手段较好的了解不同类型起搏器工作状态,检测起搏功能异常和心律失常情况。     

Time correction and two channel recording in 24 hour electrocardiographic analysis

An improved technique for automatic monitoring and analysis of ECG recording is described. The system is based on standard commercial equipment but provides improved quantitative measurement of cardiac arrhythmias. This is done by using a simultaneous recording of a 100 Hz clock, which is used to correct for tape speed variations. Also increased immunity to artefacts is achieved by combining two ECG leads, coupled with signal analysis techniques. The problems arising from certain types of artefact are also discussed.     

Physiological correlates of impedance plethysmographic waveform

A review of investigations into the origin of impedance plethysmographic waveform is presented in this article. Attempts made by several investigators in the comparison of impedance plethysmographic estimations of peripheral blood flow with that obtained by standard methods are briefly described. Investigations indicating the negligible contribution from contact impedance at body electrode interface are highlighted. Temporal correlation of impedance plethysmographic waveform recorded from thorax with various important events of the cardiac cycle is summarised and various hypotheses on the genesis of this waveform are presented.     

Simultaneous acquisition of functional magnetic resonance images and impedance cardiography

While simultaneous acquisition of electrocardiography (ECG) data during MRI is a widely used clinical technique, the effects of the MRI environment on impedance cardiography (ICG) data have not been characterized. We collected echo planar MRI scans while simultaneously recording ECG and thoracic impedance using carbon fiber electrodes and customized amplifiers. Here, we show that the key changes in impedance (dZ/dt) and features of the ECG waveforms are not obstructed during MRI. We present a method for ensemble averaging ICG/ECG signals collected during MRI and show that it performs comparably with signals collected outside the MRI environment. These results indicate that ICG can be used during MRI to measure stroke volume, cardiac output, preejection period, and left ventricular ejection time.     

Analysis of the O-wave in acute right ventricular apex impedance measurements with a standard pacing lead in animals

Modern pacemakers (implantable devices used for maintaining an appropriate heart rate in patients) can use an intracardiac ventricular impedance signal for physiological cardiac stimulation control. Intracardiac ventricular impedance from nine animal subjects is analysed and presented (seven sheep: 49.0±6.5 kg, sinus rhythm 100.3±16.5 beats min⁻¹, average impedance 629.8±72.6Ω; and two dogs: 30 kg each, sinus rhythm 86.0 beats min⁻¹, 862.1Ω and 134.0 beats min⁻¹, 1114.6Ω, respectively). The averaged curve and standard deviation curve of the impedance in sinus rhythm were analysed in MATLAB to clarify and study consistent impedance shape over one heart cycle. In eight of nine (89%) animal subjects, a consistent impedance slope change (notch) was observed in the early stage of the cardiac filling phase. This result was reproduced in an additional subject with simultaneous echocardiographical measurements of mitral valve blood flow. The notch occured soon after rapid early filling (E-wave in mitral flow) but prior to ventricular filling caused by atrial contraction, indicating that the impedance notch was caused by rapid ventricular filling and that it might be a sensed feature of diagnostic value. The intracardiac impedance notch in the present study had similar features to the non-invasive transthoracic impedance O-wave reported by others, and it is shown here that an O-wave is found in intracardiac impedance signals, strongly suggesting that the non-invasive O-wave is caused by cardiac events.