WO1989009514A1 - Artifact suppressing apparatus and method - Google Patents

Abstract

An artifact suppression circuit includes a plurality of sample and hold amplifiers. The sample and hold amplifiers are enabled at or about the time that a known artifact is expected to start. The sample and hold amplifiers are utilized to block a transfer of the artifact from a plurality of input lines to a plurality of output lines for the duration of the artifact. The duration of the hold period can be set by adjusting a mono-stable multivibrator. A second mono-stable multivibrator can be used to provide an offset pacing signal such that a hold window is formed which is initiated prior to the start of the pacing signal and which extends for the duration of and beyond the end of the pacing signal for a predetermined period of time.

Description

ARTIFACT SUPPRESSING APPARATUS AND METHOD Field of the Invention

The invention pertains to an apparatus and a method of blocking transients that appear on an input data line from appearing on an output data line.

More particularly, the invention pertains to blocking artifacts associated with transesophageal heart pacing from interfering with the operation of commonly connected diagnostic equipment. Background of the Invention

Cardiovascular disease is a very serious threat to life and health in the United States. It accounts for one-half of all deaths in the United States. Coronary artery disease is recognized as the leading cause of heart disease. It is the principle cause of death after age of 40 in men and after age of 50 in women.

Coronary artery disease kills and disables people in their most productive years. It accounts for $8.6 billion spent in 1981 for medical care. Coronary artery disease causes about 800,000 new heart attacks each year and an additional 450,000 recurrences. It is estimated that a 30-year old American male would survive to age 79 rather than 73 if coronary artery disease could be eliminated. In 1982, there were 640,000 coronary deaths in the United States. In the age range 35 to 64 about 75% of all cardiac deaths are due to coronary artery disease. Sudden, unexpected, out of hospital coronary deaths that occur too rapidly to allow arrival at the hospital while the patient is' still alive account for more than one-half of all coronary fatalities. Exa ination of the incidence, prevalence, mortality, and history of coronary artery disease suggests the need for a preventive approach. Correction of predisposing factors and innovative advances in diagnosis and therapy can make a major impact at least in reduction of coronary artery disease. This is essential since when a region of the myocardium, the heart muscle, is irreversibly damaged no current therapy can be expected to restore full heart function.

Early detection of coronary artery disease is important in reducing the extent of myocardial injury. Modern techniques of cardiology such as coronary angiography, thallium perfusion imaging, echocardiography, and radionuclide ventriculography permit highly sensitive and specific tests of myocardial ischemia (reduced blood supply to myocardial tissue) , myocardial infarction (complete lack of blood supply causing death of myocardial tissue) , and wall motion abnormalities secondary to coronary artery disease.

Unfortunately, the above noted methods are either invasive or expensive. As a result, ordinary electrocardiography and analysis of the resulting electrocardiogram (ECG) remains a very widely used, noninvasive tool in preliminary diagnosis of myocardial ischemia. Evidence of coronary artery disease is frequently identified by changes in the configuration of a certain portion of the ECG signal designated as the ST-segment. These changes manifest themselves clearly when the heart is under stress. The sensitivity and specificity of the ECG in detection of coronary artery disease can be increased by simultaneously stressing the heart. There are several forms of stressing the heart which, can be used to assess patients with chronic ischemic heart disease. These include dynamic exercise, isometric excercise, pharmacological stress, and atrial pacing.

For the past 50 years, the results of using exercise induced stress in combination with a simultaneously recorded ECG for both diagnostic and prognostic purposes have been the subject of intense research. However, not all patients are able to exercise. This can be due to obesity, poor physical condition, neuropathy, respiratory limitation, claudication, arthritis, paraplegia, lower limb amputation, diabetes, unstable angina, or risk of complication and physical incapacity in patients with recent myocardial infarction.

Cardiac stress induced by isometric exercise is often inadequate in provoking ischemic events. Pharmacological stress induced by intravenous drugs such as dipyridamole or dobutamine is commonly associated with cardiac or non-cardiac side effects, unknown pharmacokinetics for individual patients, and long delays in taking full effect. It is also ineffective in eliciting an adequate electrocardiographic response.

Transesophageal atrial pacing-induced stress in conjunction with two-dimensional echocardiography or radionuclide ventriculography has been reported to be a safe and accurate method in diagnosing ischemia. It is especially useful in patients who cannot perform an adequate exercise stress test.

Transeophageal pacing offers the advantages of direct control over the heart rate and an increased control over the degree of myocardial stress which is noninvasive. Further, it does not depend on the physical condition of the patient, and is not subjected to the wide variability in heart rates and blood pressure responses commonly associated with dynamic exercise. The esophageal route also provides a vantage point to detect posterior ischemia. The mortality rate associated with posterior abnormalities has been estimated at 15%. Eleσtrocardiographic diagnosis of posterior abnormalities such as ischemia is often difficult or equivocal. This is because no surface lead records the electrical activity" of the posterior cardiac wall directly.

Under the best of conditions, the posterior wall of the left ventricle is hidden from the chest electrodes -by the anterior wall. Electrodes located on the back of the patient are not of much use because of their distance from the heart and because of the intervening high resistivity lungs.

In contrast to the body surface, the esophagus provides a vantage from which to view the posterior aspects of the heart at close range and without intervening active or resistive tissue. Studies have shown that the esophageal ECG recorded at the ventricular level is as specifically diagnostic of posterior myocardial abnormalities as the precordial ECG is diagnostic of anterior wall abnormalities.

Nevertheless, the use of the esophageal ECG has not become popular for two reasons. First, all studies reported to the present time have used an electrode mounted at the end of a stomach tube, with considerable discomfort to the patient. Second, excessive amounts of baseline variation are present, due to the esophageal motion produced by respiration, peristalsis and cardiac contraction. These variations make it difficult to make accurate measurements, of small ST-segment shifts associated with ischemia.

Computer implementation of automatic detection of the ST-segment changes in the surface ECG and the esophageal ECG is highly desired. The goal of such a system is to provide an operator independent, reliable, and reproducible tool to aid clinicians in detection and management of myocardial ischemia of the total heart (anterior and posterior surfaces) . Several algorithms have previously been implemented in computerized electrocardiographs to analyze the surface ECG during an exercise stress test. However, these methods have been ineffective in processing the unique surface ECG recorded during a transesophageal pacing procedure. This is because the presence of large pacing artifacts alters the shape of the sensed signals and complicates computerized ECG analysis. Furthermore, to date, there has been no algorithm usable to analyze the esophageal ECG for detection of posterior ischemia. This has mainly been due to the technical difficulties that have been associated with noninvasive, high quality recording of the esophageal ECG, especially during transesophageal pacing.

Thus , there continues to be a need for apparatus and methods which make possible the processing of the unique surface ECG which can be recorded during a transesophageal pacing procedure. Preferably, such an apparatus and method will be relatively inexpensive and at the same time effective to block generated artifacts from interfering with the operation of the electrocardiograph. Summary of the Invention

In accordance with the invention a transient suppressor is provided which is usable to block a transient on an input data signal line from appearing on an output data signal line. The input data signal line can carry substantial transient electrical signals which are to be suppressed.

The suppressor includes circuitry for detecting an immediately pending transient. Circuitry is included for maintaining the value of an output electrical signal on the output line at a value substantially equal to the value of an input data signal on the input data line immediately prior to the initiation of the transient. The transient is thus blocked from the output data line. Circuitry is also included for determining when to cease maintaining the output value at the pretransient input value.

In accordance with the invention, where a transesophageal pacer is being used in combination with an esophageal pacing electrode, the transient suppressing circuitry can detect when the pacing unit generates a pacing initiating leading edge of an electrical signal. The detecting circuitry of the transient suppressor can include a mono-stable multivibrator which is triggered by the leading edge of the pacing signal. One or more sample and hold amplifiers can.be used as isolation devices between the input data signal line or lines and the output data signal line or lines.

The sample and hold amplifiers in accordance with the present invention can be triggered by an output from the mono-stable multivibrator and caused to sample the value on the respective input data signal line at the same time that the pacing unit generates the pacing leading edge. The sample and hold amplifiers can in turn provide to the respective output data line an electrical signal which has a value substantially equal to the sampled value of the electrical signal on the respective input data line. The respective sample and hold circuits will maintain the sampled values for the duration of the output pulse from the mono-stable multivibrator.

In a prefered embodiment of the invention, the pulse width output from the mono-stable multivibrator can be on the order of 11 milliseconds. This 11 millisecond time period corresponds to the duration of time that pacing generating artifacts can be expected to be present on the input data line or data lines.

Further, in accordance with the invention a second mono-stable multivibrator can be provided. The second mono-stable multivibrator is triggered by the same pacing initiating pulse as is the first mono-stable multivibrator. The second mono-stable multivibrator can be used to produce a delayed pacing pulse for the purpose of providing a window which precedes the pacing pulse. The window also extends through the duration of the expected artifact, during which the sample and hold amplifiers hold the prepacing value of the respective input data line.

In accordance with the invention, a plurality of sample and hold amplifiers can be provided so as to suppress transients between a plurality of input data lines and a plurality of output data lines. More particularly, circuitry in accordance with the present invention can be utilized to suppress artifacts generated during heart pacing. In such an embodiment, a plurality of input lines corresponds to a plurality of electrodes spaced on the body of the patient whose heart is being paced.

The plurality of output lines corresponds to a plurality of output lines coupled to an electrocardiog aph. Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings in which the details of the invention are fully and completely disclosed as a part of this specification-

Brief Description of the Drawings

Figure 1 is a side view of a patient with a previously positioned esophageal electrode; Figure 2 is a view in section of an esophageal electrode with three elements;

Figure 3 is a view in perspective of an alternate embodiment of a three element esophageal electrode? Figure 4 is an overall system block diagram in accordance with the present invention;

Figure 5 is a detailed electrical schematic of an artifact suppressor in accordance with the present invention; Figures 6A, 6B and 6C are graphs of voltages of function of time illustrative of the operation of the artifact suppressor of Figure 5;

Figures 7A and 7B represent a two chart electrocardiogram illustrating pacing artifact and base line variations as pacing current is varied; Figure 8A is a diagram of an electrocardiogram as in Figure 7A illustrating the suppression effects of the artifact suppressor of

Figure 5 at a pacing rate of 120 beats/minutes; Figure 8B is a diagram of an electrocardiogram as in Figure 8A illustrating the suppression effects of the artifact suppressor of Figure 5 at a pacing rate of 150 beats/minute; Figure 9 is an overall block diagram of an alternate system incorporating the artifact suppressor of Figure 5; and

Figures 10A-D illustrate electrocardiograms taken under various operating conditions. Detailed Description of the Preferred Embodiment While this invention is susceptible of embodiment in many different forms, there is shown in the drawing and will be described herein in detail a specific embodiment thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiment illustrated.

Figure 1 illustrates a patient P connected to a system 10 in accordance with the present invention. The system 10 incorporates a three element esophageal electrode 12. The electrode 12 is illustrated in Figure 1 located in the esophagus E and behind the heart H of the patient P. It will be understood that the esophageal electrode 12 can be located appropriately with respect to the heart H to function as intended by adjusting the vertical position of the electrode 12 in the esophagus E.

The electrode 12 carries three conductors 14, 16 and 18. In this regard, two alternate esophageal electrodes 12 and 12a are illustrated in Figures 2 and 3.

Bipolar esophageal electrodes are known in the prior art and one form thereof is described and disclosed in commonly assigned, copending United States Patent Application entitled Improved Esophageal Eleσtrocardiography Electrode, Serial No. 930,748 filed November 13, 1986. The disclosure of that application is incorporated herein by reference. With respect to Figures 2 and 3, three element esophageal electrodes can be formed with a variety of different structures. However, in accordance with Figures 2 and 3, such electrodes will include a body portion 20 or 20a which carries two spaced apart primary or pacing electrodes 14, 16 or I4a, 16a. The use of electrodes 14 and 16, or 14a and 16a is well known in connection with transesophageal pacing as described in the above-noted copending patent application. The electrodes 12a or 12b each are provided with a three conductor cable 22 or 22a. The cable 22 or 22a, in addition to being used to position the electrode 12 or 12a in the esophagus E provides electrical connection therewith. Two of the conductors of the cable 22a, associated with pacing electrodes 14 and 16, form a two conductor cable 22b. The third conductor associated with the third electrode 18, is available as a single conductor 22c. Figure 4 illustrates the elements of the system 10 coupled to the patient P. In addition to the three element electrode 12, the system 10 includes a transesophageal cardiac stimulator or pacer 30 of a conventional type. For example, the pacer or stimulator 30 could be an Arzco Medical Electronics, Inc. Model 7.

As is conventional, the stimulator or pacer 30 is coupled via the two conductor cable 22b to the two electrodes 14 and 16 for transesophageal pacing. The stimulator or pacer 30 is also coupled via a communication cable 32 to a stimulator artifact suppressor 34.

As will be discussed further subsequently, the artifact suppressor 34 includes a plurality of inputs 36 and a plurality of outputs 38. The inputs 36 can vary based on the type of application in which the suppressor 34 is being used.

In an embodiment where the suppressor 34 is being used in combination with the three element electrode 14, the inputs 36 include the conductor 22c coupled to the third conductor 18 of the esophageal electrode 12. The inputs 36 also include a surface electrode 39a located on the manubrium of the patient P and coupled by a conducting member 40a to the suppressor 34.

The set of inputs 36 also includes a connection to a surface electrode 39b at the C5 anatomical position of the patient. The C5 electrode is coupled via a conducting member 40b to the respective input of the suppressor 34.

Finally, the inputs 36 include a connection to a surface electrode 39c coupled to the right leg of the patient which serves as the system electrical ground. The right leg electrode is coupled via a conducting member 40c to a respective input of the suppressor 34. The surface electrodes 39b and 39c at the C5 position and the right leg position are conventional electrode positions used in connection with electrocardiography. Conventional electrocardiographs have a total of 10 inputs which include inputs from a right leg surface electrode, a right arm surface electrode, (in the present instance replaced by the manubrium electrode connection), a left arm surface electrode, (replaced in the present system by the connection to the third electrode 18 in the esophageal electrode) , a left leg surface electrode (replaced in the present system with a connection to the C5 anatomical electrode) and standard chest electrodes C1-C6. The system 10 is useful with standard electrocardiographs for the purpose, when utilizing a three element esophageal electrode such as electrode 12, for providing a two channel-system usable in detecting posterior anterior and cardiac wall abnormalities. The system 10 is particularly useful with patients who are unable to perform an adequate exercise stress test. In this system, the stimulator 30 in conjunction with electrodes 14 and 16 of the esophageal electrode 12 can be used to pace the heart at elevated rates for diagnostic purposes without any necessity of having the patient physically exercise at the same time.

Further with respect to Figure 4, the four inputs to the artifact suppressor 34 on conductors 22c, 40a, 40b and 40c are processed by the artifact suppressor 34. The processed results can be transmitted by the output data lines 38 implemented as a cable 44 having at least four conductors 44a, 44b, 44c and 44d to the electrocardiograph 48. The four conductors of the cable 44 are coupled respectively to the left arm, the right arm, the left leg and the right leg inputs of the electrocardiog aph 48. A two chart output results which can be used for anterior and posterior analysis of the heart H.

It will be understood that the electrocardiograph 48 is a conventional 10 lead electrocardiograph of the type known to those skilled in the art as well as practicing clinicians. However, with respect to the system 10 of Figure 4 only four of the input leads to the electrocardiograph 48 are being used.

The input dynamic range of typical electrocardiographs can be as large as + 10 mV. On the other hand, assuming a typical pacing current of 20 mA and a patient equivalent impedance of 1000 ohms, the potential that is developed in the esophagus can be as high as 20 V which is outside the input dynamic range of standard electrocardiographs. Due to this inherent limitation of electrocardiographs, it is necessary to suppress the large pacing artifacts. Suppression can be obtained by different methods. For example, during the delivery of the stimulation pulse, the inputs of the recording amplifier of the electrocardiograph can be shorted together or disconnected from the signal source. However, in these cases switching artifacts appear since the amplifier is switched from a nonzero output to a zero output. These switching artifacts are often large, and hence, the above do not offer a satisfactory solution to the problem. In accordance with the present invention, the suppressor 34 provides an improved and more satisfactory solution.

Figure 5 is a detailed schematic diagram of the suppressor 34. The circuitry of Figure 5 suppresses large pacing artifacts before those signals can enter the electrocardiograph 48. Hence, saturation of the electrocardiograph 48 is avoided. Since the suppressor 34 is located between the input data lines 34 and the output data lines 36, the integrity of the signals on the lines 34 must be maintained.

National Semiconductor LF398 sample and hold circuits 50-66 are used to block artifacts on the input lines 36 from appearing on the output lines 38. Each sample and hold amplifier operates as a unity gain follower (gain error < 0.004%) in the sample mode. Each has fast acquisition time (^lOxts), high input impedance (10 G ohms), wide bandwidth (100 kHz) , low output impedance (0.5 ohms) , very low output noise (50 to 30 nV/Hz 1/2 in the sample mode, and 130 to 50 n V/Hz 1/2 in the hold mode, in the frequency range 1 to 100 Hz) , and differential sample-hold logic threshold of 1.4 V. As a result, the integrity of the signals on the input lines 36 is not compromised by the suppressor 34 which is located between the patient P (signal source) and the electrocardiograph 48.

The circuitry in the suppressor 34 receives inputs on the cable 32 from the transesophageal cardiac stimulator 30. The stimulator 30 is capable of delivering square wave constant current pulses of up to 40 mA in amplitude, 10 ms in width, and 600 pulses per minute across impedances of up to 3000. As Figure 5 illustrates, a down going pacing signal S3, from the stimulator 30 is coupled via the cable 32 and an optoisolator 70 to a Schmitt trigger 72. The down going output of the Schmitt trigger 72 switches the monostable multivibrator 74. The down going output pulse of the mono-stable multivibrator 74 provides a control signal 76 for the sample and hold circuits 50-66. When this signal is high about 9 volts, the circuits 50-66 are in a sample mode. When it is low about zero volts, the circuits 56-66 are in a hold mode. In the sample mode, the outputs of the circuits 50-66 closely follow their corresponding input signals. In the hold mode, the values of the input signals just before switching are held and the outputs are equal to the corresponding, held input values. It has been found that the combination of a hold capacitor value of IO ΛAF in series with a 1 koh resistor yields optional results taking into accounts droop rate and other factors. The hold duration is controlled by varying the pulse width of the output of mono-stable multivibrator 74 which is determined by a 100 kohm potentiometer 78. This control provides a range of hold duration or blanking period from 0 to 25 ms. Figure 6 illustrates a plurality of graphs of voltages as a function of time which further explain the operation of the suppressor 34. In graph Fig. 6A, the pacing signal S3 generated in the stimulator 30 on the cable 32 is illustrated. The pacing signal has a period on the order of 100-1000 milliseconds. The graph of Figure 6B illustrates the output of the mono-stable multivibrator 74 on the line 76, is the hold signal. The hold signal or blanking signal can be adjusted to have a duration between 0 to 25 milliseconds.

The graph of Figure 6C, illustrates the pacing signal generated by the stimulator 30.

In the system of Figure 5, the pacing function is initiated when the signal S3 on the line 32 makes the down going transistion thereon which triggers the mono-stable multivibrator 74, best illustrated in Figure 6C. It will be understood that a prepacing window could be introduced by delaying the application of the signal on the line 32 to the esophageal electrode 12. This could readily be accomplished by introducing a second mono-stable multivibrator into the circuitry 34. This second mono-stable multivibrator will be driven by the output of the Schmitt trigger 72. The second multivibrator could be provided with a relatively -16- short delay period, on the order of 5 milliseconds. Output from the second mono-stable multivibrator could then be fed back to the stimulator 30 to trigger the pacing signal on the conductors 22b. In such an instance, the sample and hold control signal on the line 76 will go low on the order of 5 milliseconds before the pacing signal is initiated on the cable 22b.

Figures 7A and 7B illustrate the type and magnitude of artifacts generated by the stimulator 30 as the operation of that unit has been known from the prior art. Figure 7A is one chart off of the ECG 48 illustrating signals on the esophageal/manubrium lead combination 22c/40a. Pulses 100 and 102 of the graph of Figure 7A illustrate a QRS signal as is known in the prior art. Immediately following the QRS signal, pulses 104 and 106'are pacing artifact signals generated in response to pacing output from the stimulator 30. In addition to the artifact pulses 104 and 106 which are injected between the diagnostically useful QRS pulses 100 and 102, the base line of the signal in Figure 7A drifts substantially as pacing current is increased.

In Figure 7B, a plot of the combination of the C5 anatomical electrode and the manubrium electrode is illustrated. Once again, the QRS pulses, such as pulses 120 and 122 are followed by pacing artifact pulses 124 and 126.

In contradistinction to the graphs of Figure 7 which were prepared without using the suppressor 34, graphs from Figure 8A and 8B utilizing the same electrode combinations but with the suppressor 34 present as in Figure 4 display complete blanking of the artifact effects as well as steady baseline. In Figures 8A and 8B the patient's heart beat has been captured by the stimulator 30 at a time indicated at 136. Capture heart rate corresponded to 120 beats per minute. With respect to Figure 8A, the QRS signals,

140 and 142 are being generated in response to the pacing signals from the stimulator 30 at a rate of 120 beats per minute. Figure 8A corresponds to Figure 7A in that it is a chart of the esophageal/manubrium electrode input combination to the electrocardiogram- 48.

Figure 8B illustrates a corresponding electrode combination as in Figure 7A of the esophageal/manubrium electrode input combination. The chart of Figure 8B also exhibits complete blanking of the pacing generated artifacts and a steady baseline. The QRS pulses are clearly illustrated as pulses 150 and 152 also corresponding to a captured heart rate at 150 beats per minute. The suppressor 34 can also be used in a system 160 as in Figure 9. In the system 160, the stimulator 30 is used in combination with a standard two element esophageal electrode 162 of a known type. In accordance with the system 160, the standard 10 electrocardiograph electrodes are located on the patient P as is conventional in connection with electrocardiography.

A standard 10 electrode patient cable 164 can be used. The 10 electrodes are coupled through the 10 inputs of the suppressor 34 as illustrated in Figure 5. In the embodiment of the system 160, all 10 electrodes are connected to corresponding inputs to the suppressor 34. A standard 10 conductor cable 166 is used to couple the output lines of the suppressor 34 to the electrocardiograph 48. If desired, the electrocardiograph 48 could be a conventional analyzing, computerized system often used for analyzing exercise stress, ECG. Such devices are especially suited for providing immediate analysis of a set of input signals. However, they are completely unable to analyze input signals in the presence of pacing artifacts, such as the artifacts illustrated in Figures 7A and 7B. Hence, the system 160 of Figure 9 enables the esophageal stimulator 30 to be used in combination with a computerized electrocardiograph and- obtain the immediate benefits of the automated analysis that such units provide.

Figure 10A is a chart generated by a commercially available computerized exercise electrocardiogram system (Marquette CASE-12) . The unit was coupled to a patient as is conventional with surface electrodes, no pacing of any type was used.

Figure 10A illustrates, from bottom to top, a signal from the surface lead conventionally identified as V6, a signal from the surface lead conventionally identified as V4, a signal from the surface lead conventionally identified as aVF, a signal from the surface lead conventionally identified as V5, a signal G2 from the internal trigger logic of the unit indicative of QRS complexes in the surface leads is formed from thresholding the top signal Gl.

Signal Gl is in turn conventionally formed by squaring several surface leads, adding them and taking the square root of the result. For each occurance of a QRS complex in the surface leads, a pulse is present in the signal G2. These pulses confirm the presence of a QRS complex. The computerized system uses this information to locate the ST-segment for ST measurements believed to be important in diagnosis of coronary artery disease. -19- In Figure 10A, the associated, unpaced heart rate of the patient was sensed as 79 beats per minute.

In Figure 10B, the same exercise electrocardiograph unit was used in connection with a transesophageal paced heart. For pacing purposes, a conventional two element esophageal electrode as noted previously was used. The Arzco Model 7 stimulator previously noted was also used. The system was arranged as generally indicated in Figure 9 without the suppressor 34 between the patient and the electrocardiogram 48.

The pacing heart rate was 130 beats per minute. As can be seen in Figure 10B, the shape signal G2 of the computerized system has been distorted by the presence of large pacing artifacts (the large pulses in Figure 10B) in the surface electrode leads which occur during pacing stress. Thus, the computerized system could not function properly and no ST-segment measurements were properly reported. Also, the heart rate determined by the system was uncorrectly reported as 194 bpm. This did not correspond to the pacing heart rate of 130 bpm.

Figure 10C illustrates the operation of the stimulator 30 and the same exercise electrocardiogram system coupled to the suppressor 34 as in Figure 9.

The large pacing artifacts have been suppressed. The signal G2 is similar in shape to the signal G2 in Figure 10A. Each pulse in the signal G2 corresponds to the QRS complex detected in the surface electrodes. The pacing rate when the graphs of Figure

10C were generated was 130 beats per minute.

In the Figure 10C, the heart rate was correctly determined by the electrocardiograph as 127 bpm close to the pacing rate of 130 bpm. -20- Figure 10D is similar to Figure IOC. Figure 10D was generated with a system as in Figure 9. In addition. Figure 10D illustrates the ST-segment measurements in the top 2 waveforms which the electrocardiogram reported during a pacing session at 130 bpm with the suppressor 34 operating. In this instance, the heart rate was reported by the electrocardiogram as 129 beats per minute. This was very close to the pacing rate of 130 beats per minute. Hence, the suppressor 34 enables the use of commercially available electrocardiographs in conjunction with transesophageal pacing. This heart stress modality can be used with those patients who cannot perform an adequate conventional dynamic exercise stress test.

It will also be understood that alternate types of circuitry could be used without departing from the spirit and scope of the present invention. For example, instead of sample and hold circuits, -digital circuits could be used to store a digitized input data value. That value could be converted to analog form and presented to an output data line.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the novel concept of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Claims

What Is Claimed Is;

1. A transient suppressor usable with an input data signal line and an output data signal line, the input data signal line being subject to transient electrical signals, the suppressor comprising: means for detecting an immediately pending transient; means for maintaining an output electrical signal on the output line at a value substantially equal to the value of a selected pre-transient input signal on the input line for the duration of the transient on the input line; and means for determining when to cease maintaining said output value at said pre-transient input value.

2. A transient suppressor as in claim 1 with said detecting means including transition sensitive switching means.

3. A transient suppressor as in claim 1 with said maintaining means including sample and hold amplifying means.

4. A transient suppressor as in claim 1 with said maintaining means including means for storing an analog representation of a selected value of the input data signal.

5. A transient suppressor as in claim 1 with said maintaining means including means for storing a digital representation of a selected value of the input data signal.

6. A transient suppressor as in claim 1 with said determining means including means for indicating passage of a predetermined time interval.

7. A transient suppressor as in claim 6 with said indicating means including means for generating at least one electrical pulse of a predetermined duration.

8. A transient suppressor as in claim 6 including counting means for determining the passage of a predetermined time interval.

9. A transient suppressor comprising: a plurality of input lines; a plurality of sample and hold means with each of said sample and hold means coupled between a respective input line and a respective output line, and control means for simultaneously activating said hold function of at least some of said means for a predetermined period of time in response to the presence of a selected condition.

10. A method of inhibiting a transient on an input data signal from appearing in an output electrical signal comprising: detecting a pending transient; maintaining a value of the output electrical signal at a value substantially equal to the value of the input data signal at a selected time for the duration of the transient on the input signal; and determining when to cease maintaining the output value at the pre-transient input value.

11. A method as in claim 10 including in the maintaining step, sampling a value of the input electrical data signal and holding the sampled value for the duration of the transient.

12. A method as in claim 10 including generating a control signal in response to detecting the immediately pending transient.

13. A method of inhibiting artifacts generated during transeophageal pacing comprising the steps of: detecting when an electrical pacing pulse is to be transmitted to the patient; isolating a portion of electrical signal wire from the patient connected electrode; maintaining a value of the electrical signal in the isolated portion at a value substantially equal to the value of the signal from the patient connected electrode for the duration of the artifact; and determining when to cease the maintaining step.

14. An artifact suppressor usable with an artifact sensitive data signal carried by a selected conductor comprising: means for detecting an immediately impending artifact; means for storing a current value of the data signal in response to detecting the impending artifact and means for determining when said artifact has passed and for replacing the stored value with a post-artifact value of said data signal.

15. An artifact suppressor comprising: means for receiving, in parallel, a plurality of data input signals; means for storing each received data input signal in response to receipt of a selected control signal; means for transmitting, in parallel, a plurality of data output signals; and control means, responsive to a selected timing input signal, for generating said control -24- signal, for storing a selected value of each_, of the data input signals and for transferring each said stored data input signal to a respective member of said plurality of output signals for a predetermined period of time;

16. An artifact suppressor as in claim 15 with said storing means including at least one sample and hold amplifier.

17. An artifact suppressor as in claim 15 with said storing means including means for storing digital representations of the received data input signals.

18. An artifact suppressor as in claim 15 with said control signal generating means including means for switching said control signal to a storing state for a predetermined period of time.

19. An artifact suppressor as in claim 18 with said switching means including a mono-stable multivibrator.

20. An artifact suppressor for blocking transients on a set of input lines from appearing on a set of output lines comprising: a plurality of sample and hold amplifier means; means for coupling each input line to a respective amplifier means; means for coupling each output line to a respective amplifier means; and control means, coupled to said plurality of amplifier means, for generating a common amplifier means switching control signal with each said amplifier means sampling signals on the respective input line when said control signal is in a first state, each said amplifier means storing a signal present on the respective input line when said control signal is in a second state and transferring said stored signal to a respective output line.