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Aids to electrical diagnosis of pacemaker failure
Aids
to electrical
diagnosis
of pacemaker
failure
E. Dekker, M.D.* J. Biiller, M.D. 21. M. Schuilenburg, M.D. Amsterdam, Netherlands
T
he electronic pacemakers used in the therapy of atrioventricular block are still far from perfect. With a considerable percentage of them, we must face the sometimes grave emergencies in patients returning with pacemaker failure. Proper treatment of this condition is based on the correct diagnosis of its cause. However, a complete set of diagnostic rules for the analysis of pacemaker failure is not yet available. Only a very few studies’J have concentrated on this subject. It is the purpose of this paper to present experience with a few diagnostic methods which have proved to be helpful in solving some of the electronic riddles of this new syndrome. These will be presented in a systematic form, followed by some summaries of cases in patients during treatment of whom this system gradually evolved. Methods
1. Prefailure documentation of the pacemaker function. Analysis of pacemaker failure is greatly facilitated by comparing the postfailure clinical and electrical symptoms with records of the prefailure function. Pacemaker failure is frequent enough to warrant documentation of the prefailure status in every case. This applies both to the function of the pacemaker proper and to the patient-pacemaker combination. From the Department of Cardiology and Received for publication Jan. 18, 1965. *Address: Afdeling Cardiologie en Klinische
739
Clinical Fysiologie,
A.
DOCUMENTATION
OF
PACEMAKER
FUNC-
Before connection of a new pacemaker to a patient its behavior in vitro, by means of an oscilloscope and a series of load resistances, which can be selected by means of a multipolar switch, is tested. Rleasurement of the voltage over each resistor will at the same time allow calculation of the current through it. The pulse rate of the pacemaker at each of these resistances should be noted. In some types of pacemakers the rate is dependent on the external load. In case of wire breakage this change in rate may prove to be helpful in diagnosis. TION.
B.
DOCUMENTATION
OF
FUNCTION
OF
THE
In the postoperative period the course of the wires over their full length and the position of the electrodes are documented for future reference by means of x-ray films. Furthermore, a standard electrocardiogram is obtained for the documentation of the direction and amplitude of the pacemaker artifacts. Proper attention is given to pacemaker rate after implantation, since a subsequent change in rate is an important sign of altered and probably disturbed function. In patients with disconnectable wires and external pacemakers the threshold and resistance of each wire are measured at least once in the postoperative period, by the PACEMAKER-PATIENT
Physiology, Wilhelmina
University Gasthuis,
COMBINATION.
of Amsterdam.
Amsterdam.
Amsterdam,
Netherlands.
Netherlands.
740
Dekker,
Bailer,
and Schuilenburg
methods discussed below, before the patient is discharged from the hospital. It is a considerable advantage of external pacemakers with internal electrodes that electrode resistance and threshold can be regularly checked. 2. Postfailwe analysis. The clinician should decide whether the cause of failure is localized in the pacemaker proper, in the wire-electrode combination, or in the patient’s heart. This decision is facilitated by the following methods: A. ELECTROCARDIOGRAPHY. The ECC; gives four types of information. It will record the rate, direction, and amplitude of the pacemaker artifacts and the form and behavior of the ventricular complexes. The pacemaker rate is compared to the prefailure rate. Any changes in rate should be interpreted in the light of the predetermined dependence of pacemaker rate on load resistance. Wire breakage usually causes higher resistance in the patient circuit because of the smaller surface of the broken wire. The direction and magnitude of the pacemaker artifacts is carefully compared to the prefailure record. A change in amplitude and direction of the pacemaker artifact is very suggestive of failure in the electrode-wire combination. The mechanism underlying this change is indicated in Fig. 1. The electrodes constitute an electrical dipole the vector of which changes its direction when the wire breaks. A large displacement of an electrode has a similar influence. The electrocardiogram also pro-
Fig. 1. Schematic diagram the pacemaker stimulus breakage of a pacemaker
of the electrical before (A) and wire.
vector of after (B)
.4m. Heart J. llrrrmber, 1965
vides a record of the behavior of the ventricular complexes. Each pacemaker artifact which falls outside the refractory period of spontaneous ventricular activity should be followed by a ventricular complex. Even a single instance of failure of the ventricle to follow the pacemaker should be viewed with the greatest suspicion. Therefore, long strips of record should be obtained and the effect of deep respiration and change of body position noted. Shortly after wire breakage it is common for the broken ends of the wire to maintain mechanical contact, except during special body positions or respiratory maneuvers. The QRS complexes may change their outline because the ventricles change from bipolar to unipolar stimulation (Fig. 2,A and B). B. ROENTGENOLOGY. The x-ray film may show a displacement of the wires and electrodes. If superposition of wire shadows is avoided, it may also show the localization of wire breakage. However, it should be stressed that the x-ray films must be of an optimal quality, and that a site of breakage may easily be overlooked unless the entire course of the wires is very patiently scrutinized. C. CONSTRUCTION OF ISOPOTENTIAL LINES OF THE PACEMAKERARTIFAcTON THE TRUNK.
This procedure may give useful information about the site of wire breakage and the polarity of the broken wire. Exploration with a precordial electrode to find the locus of all points at which the pacemaker artifact is zero establishes the approximate “zero” voltage line. Then isopotential lines can be mapped out by using a bipolar lead, say Lead I. The “right arm” electrode is fixed at an arbitrary site on the trunk, and the “left arm” electrode is moved around until once more the locus of all the sites at which the pacemaker artifact shows zero potential with respect to the “right arm” electrode is found. The result of this mapping is a series of more or less concentric curves surrounding sites of maximal positivity and negativity (Fig. 3). Directwriting electrocardiographs have such a low-frequency response as to pass only a small proportion of the voltage of the pacemaker artifact. Therefore, mapping of the isopotential lines is preferably done with the aid of an oscilloscope. It follows
Aids to electrical diagnosis
of @acemaker failure
741
Fig. 2. Electrocardiograms Leads I, II, and III from Patient D in the early postoperative period (A), after breakage of a wire (B), and after grounding of this wire and breakage of the second wire (C). Direction and amplitude of the pacemaker artifacts are changed in B and C. The artifact-artifact (au) interva1 is shorter in B and C.
Fig. 3. Mapping of isopotential lines on the trunk of Patient D after the first wire breakage ping of the insulation from the positive wire near the pacemaker and breakage of the second through the diaphragm (B).
(A ), and after stripwire near its passage
742
Dekker,
from the concept of the voltage distribution of an electrical dipole in a conducting rnedium that the zero line should be approximately at right angles to the electrical dipole constituted by the electrodes or wire ends. Furthermore, some relationship exists between the site and polarity of the voltage maxima on the surface and the spatial site of the poles of the dipole. The sites of maximal positive and negative voltage, therefore, aid in the roentgenologic localization of the wire breakage. If the relative position of the two poles has been identified roentgenologically, it is often easy to tell from the combination with the pattern of the isopotential lines whether the positive or the negative wire is broken. This clinical application of the isopotential lines will be exemplified below. D. AND
DETERMINATION RESISTANCES
OF OF
Am. Heart 1. December. 1965
an.d Schuilenburg
Biiller,
THE
THE
THRESHOLL)
WIRE-ELECTRODES.
If no fault can be found by this exploration of the electrode-wire combination, a high stimulation threshold of the myocardium should be excluded as a cause of failure. This is done simultaneously with the determination of wire-electrode resistance. In patients with implanted pacemakers it is generally necessary to interrupt the continuity of the skin in some way in order to establish an electrical contact with the wire. If the pacemaker pocket is opened during this procedure, the wires can be separated from the pacemaker, and each wire is then individually tested against an indifferent electrode, for example, a subcutaneous needle. (Jnder aseptic precautions the electrodewire to be tested is connected to an external pacemaker with a continuously adjustable output current. This current is measured by means of the voltage appearing over a resistor of known magnitude placed in series with the wire to be tested. If this voltage is measured on a dual-trace oscilloscope screen simultaneously with the voltage appearing between the electrode-wire and the indifferent electrode, the total resistance of these electrodes and the patient can be calculated. The Medtronics implanted pacemaker384 has a special provision for this measurement. The stimulating current is varied in order to find the threshold level for each electrode. If during the same session the implanted pacemaker is con-
netted by sterile electrical wires to the same series of load resistors used in preoperative control, its response can be measured and compared with preoperative performance. 3. Therapeutic measures. These are determined by the outcome of this analysis. A failing pacemaker is exchanged. If the threshold is increased, the pacemaker can sometimes be replaced by another type, if necessary by an external pacemaker, with higher output current. In the case of wire breakage or electrode displacement of one of a pair of myocardial electrodes, stimulation can be re-established by unipolar stimulation using an indifferent electrode. For this purpose the broken wire can be used if it is stripped of its insulation. This may be done near the pacemaker.5 In those types of pacemakers in which the polarit) of the wire cannot be recognized from the outside, determination of the polarit) through the intact insulation may be accomplished by a pole analyzer using the principle outlined in Fig. 4, in which the pacemaker with its wires is schematically represented. Current through the lvires induces a circular magnetic field in the direction indicated. If the current increases
0
* -. r;
-L +
Fig. 4. Schematic diagram of the pole analyzer. The pacemaker with its positive and negative electrode wires is indicated. Arrows indicate the circular magnetic field surrounding the turns of the coil. Mounted left and right below are oscilloscope pictures from the output signal from the coil when applied to a negative and a positive wire, respectively. A 1 ,OOO-ohm damping resistor is used
l’ohme Nzcmber
70 6
Aids LOelectrical diagnosis of pacemaker failure
743
Fig. 5. Practical construction of the pole analyzer. It consists of 520 turns of 0.20~mm. enameled copper wire on a Perspex core. Franz left to right: Aluminum cap for shielding the signal from interference emitted by the pacemaker proper, the pole analyzer applied to an electrode wire, and a diagram of the core construction.
during the rise time of the pacemaker pulse, a voltage spike is induced at the output of a coil held in close approximation to the wire. During the fall time of the pacemaker pulse a second spike is induced with opposite polarity. The practical construction of this simple device is illustrated in Fig. 5. Confusion is avoided by making the connections in such a way that during the actual preoperative identification a simple rule of thumb can be followed, whereby the first output spike should be positive if the coil is put around the positive wire in such a way that a letter P written on the coil points toward the pacemaker. Finally, if all wires are broken, or if their threshold has risen beyond the reach of pacemaker power, application of new electrodes, if necessary by a second thoracotomy, may become a necessity. Case summaries In PatientA, a 74-year-old man with a history of recurrent Stokes-Adams attacks and complete atrioventricular block, a Medtronics double wireelectrode was inserted on Sept. 9, 1961, and connected to an external pacemaker. On Oct. 27, 1961, pacemaker failure occurred. Resistance measurement of the wires showed a normal value for the negative wire (100 ohms) and a high resistance of the positive wire (3,900 ohms). A subcutaneous
needle in the abdominal wall was used as an indifferent electrode, and unipolar pacing was resumed. On Nov. 20, 1961, it was found that the pacemaker artifacts disappeared from the electrocardiogram on deep inspiration. The resistance of the remaining myocardial electrode-wire was now found to be very high on deep inspiration. It was concluded that this second wire was also broken. A second thoracotomy was performed on Nov. 25, 1961, and four ElemaG electrodes were implanted and connected to an external pacemaker. This combination functioned well until the patient’s death from multiple myeloma on Nov. 25, 1963. woman, a Medtronics In PatientB, a 52-year-old internal pacemaker was implanted elsewhere on Oct. 21, 1962, because of complete atrioventricular block with repeated Stokes-Adams attacks. On March 29,1963, she was admitted to our department for evaluation of a complaint of vague trembling sensations in the abdominal wall at the pacemaker site. No special attention was paid at that time to the small amplitude of the pacemaker artifacts. On Aug. 2, 1963, the patient died suddenly at home. Postmortem examination revealed an intact wireelectrode system. Examination of the pacemaker, however, showed that the output current had dropped to very low values, and the conclusion was that failure of the pacemaker proper was responsible for the patient’s sudden death. Patient C, 50 years old, suffered from complete atrioventricular block with recurrent Stokes-Adams attacks. On March 23, 1962, four epicardial electrodes were implanted and connected to an Elema external pacemaker.6 The batteries were changed on July 4, 1962. In January, 1963, the pacemaker rate showed a gradual rise: this was corrected else-
744
Dekker,
.4m. Heart J. lirrcmber, I965
Biiller, and Schuilenbztrg
where by repeated readjustment of the rate controls. Unfortunately, too little attention was paid to this phenomenon. On Feb. 2, 1963, the patient died suddenly. At autopsy the wires were found to be intact, but two of the batteries were exhausted. Patient D, a male, had a history of repeated Stokes-Adams attacks caused by complete atrioventricular block. On July 5, 1963, an Electrodyne TII 14 internal pacemaker was implanted. On Jan. 10, 1964, the patient presented with the complaint that he had observed a rise in his pulse rate from 6.5 to 70 per minute. This observation was confirmed by comparison with the record made previously (Fig. 2,.1 and B). Besides, it was noted that the direction and amplitude of the pacemaker artifacts had changed. Although every pacemaker artifact was followed by a ventricular complex, a wire breakage was suspected. This could not be found on the initial x-ray films. Since the pacemaker had made a quarter turn under the influence of pressure from the waist belt, it was suspected that the breakage might be situated near the pacemaker. Mapping of the isopotential lines on the trunk (Fig. 3,.4) showed that the two voltage maxima were far from the pacemaker, thus making the assumption of breakage in its neighborhood very unlikely. The zero line and the isopotential lines surrounding the maxima were marked by copper wire, and on the x-ray frhn thus obtained (Fig. 6) the breakage
point was found to be near the positive maximum. It was clear from this x-ray film that the intact electrode was superior and to the left of the broken wire, and that, therefore, the broken wire must have a positive polarity. On Jan. 20, 1964, both wires were exposed near the pacemaker, and the positive wire was identified by means of the pole analyzer (Fig. 5). Continuity of the electrical circuit was re-established by “grounding” this wire in the surrounding tissues by removing the jnsulation over approximately 2 cm., after which the pacemaker performed satisfactorily. was renewed pacemaker On Jan. 27, 1964, there failure. The electrocardiogram showed a 2:l atrioventricular block and a renewed change in the direction and amplitude of the pacemaker artifacts (Fig. 2,C). The pattern of the isopotential lines was thoroughly changed. The center of maximal positivity was seen near the pacemaker, where the positive wire had been bared, and the maximal negativity was found near the heart (Fig. 3,B). The voltage maxima corresponded we!l with the location of these poles on the x-ray film (Fig. 7). On Feb. 5, 1964, another thoracotomy was performed and an internal Elema pacemaker \vas implanted with two functioning and two spare electrodes. Until now the patient is doing well. Patient E, a 75year-old man who had had several Stokes-Adams attacks, was given an Electrodyne TK 14 internal pacemaker on Oct. 18, 1963. On
Fig. 6. The zero line and some isopotential lines marked by copper wires ponc hng to Fig. 3,:1. Insert: The site of wire breakage (slightly retouched).
on the x-ray
film
of Patient
D, c:0*
l-es-
Aids to electrical diagnosis
of pacemaker
failure
745
become complete. An x-ray film made shortly before operative exploration showed that the intact wire electrode was displaced and had possibly slipped out of the myocardium. Indeed, after identification with the pole analyzer and grounding of the positive wire, the heart could no longer be stimulated from the negative electrode. Both wires were withdrawn. One proved to be broken near the electrode: the other was intact and must previously have lost contact with the myocardium. On March 2, 1964, a permanent intracavitary electrode? was introduced and connected to an implanted pacemaker. Patient F, a 74-year-old man, had also a history of repeated Stokes-Adams attacks and a complete atrioventricular block. On Dec. 18, 1963, an Electrodyne TR 14 pacemaker was implanted. On Jan. 17, 1964, the patient observed irregularity of his pulse beat. The pulse rate was 48 per minute. An electrocardiogram showed only occasional stimulation of the ventricles. The pacemaker rate was somewhat higher than shortly after the operation. The amplitude and direction of the pacemaker artifacts were changed. The x-ray films showed breakage of one of the two wires. Comparison of the x-ray findings with results of the mapping of the pacemaker isopotentials on the trunk led to the conclusion that the broken wire had a negative polarity. After exposure of the wires the negative wire was identified through the intact insulation by the method described above. Its grounding restored pacemaker function. Two days later the heart rate again fell to 40 per minute. The electrocardiogram showed that tota failure followed the pacemaker. The chest x-ray film showed that the second wire was also broken. An Elema pacemaker with two spare wires was implanted on Jan. 31, 1964. The patient is doing well up to the present time.
Discussion
Fig. 7. Zero lines and some isopotential lines marked by copper wires on the x-ray film (Jan. 27, 1964) of Patient D, corresponding to Fig. 3,B. Maximal positivity is found near the pacemaker, where the stripped positive wire is imbedded. The area of maximal negativity surrounds the end of the broken negative wire.
Feb. 11, 1964, a routine electrocardiogram showed intermittent failure of the pacemaker. Amplitude and direction of the pacemaker artifacts were changed and their frequency was slightly higher than that shortly after operation. A chest x-ray film showed that one of the wires was broken near the heart. Comparison of the radiologic findings with the pattern of the isopotential lines led to the conclusion that the polarity of the broken wire was positive. Preparations were made for the “grounding” of this broken wire. Meanwhile, pacemaker failure had
The ease of control of wire integrity in patients with internal electrodes attached to an external pacemaker is exemplified in Patient A, in whom measurement of resistances led to a diagnosis of wire breakage. In other similarly treated patients, not included in this series, high thresholds nornlal resistances, probwere found with ably pointing to the development of connective tissue around the electrodes. Connecting the pacemaker to a spare electrode forestalled failure. Failure to pay attention to the small voltage of the pacemaker artifacts and to the change in pacemaker rate, respectively, may have contributed substantially. to the death of our Patients B and C. The case summaries of Patients D, E, and F awareness of the reflect our increasing significance of changes in rate, in direction, and amplitude of the pacemaker artifacts
746
Dekker,
Bdler,
Am. Heart J. Decmbar, 1965
and Schuilenburg
and the use of the combined results of x-ray examination and mapping of the isopotential lines of the pacemaker artifact on the trunk of the patient. The broken wire was operatively exposed and correctly identified by the pole analyzer, and pacing was restored after “grounding” of the broken wire in Patients D and F. Therapeutic successwas of disappointingly short duration because of breakage of the second wire shortly after the first. No explanation is offered for the remarkable similarity in lifespan of a pair of implanted wires in these cases, but it is assumed that in other cases the second wire may remain intact for considerably longer periods. It is hoped that in such cases the methods outlined above may add to the lifespan both of the pacemaker system and the patient. Summary
Some aids to electrical diagnosis of pacemaker failure are described. These consist of careful preoperative appraisal of pacemaker function and immediate postoperative electrocardiographic recording of rate and form of the pacemaker artifacts, and of the postfailure comparison of these same features. Mapping the isopotential lines of the pacemaker artifacts on the patient’s trunk, in combination with x-ray analysis, aids in the localization of wire breakage and in the determination of the
polarity of the broken wire. Some therapeutic implications of this analysis are exemplified and discussed. We wishto expressour gratitude to Prof. Durrer for his helpand support,to Prof. Dr.
Dr. D. L. H. van der Tweel for his invaluable help in the early phases of our pacemaker troubles, and to Prof. Dr. B. G. Ziedses des Plantes and his staff for their contribution to Figs. 6 and 7. REFERENCES 1. Parsonnet, V., Gilbert, L., Zucker, I. R., and Asa, M. M.: Complications of the implanted pacemaker. A scheme for detection of the cause bf the defect and methods for correction, J. Thoracic & Cardiovas. Sure. 45:801. 1963. 2. Kantrowitz, A.: Implant~ble carhiac pacemakers, Ann. New York Acad. SC. 111:1049. 1964. 3. Chardack, W. M., Gage, A. A., and Greatbatch, W.: Correction of complete heart block by a self-contained and subcutaneously implanted pacemaker, 1. Thoracic & Cardiovas. Surg.._ &814, 1961.4. Chardack. W. M.. Frederico. A. 1.. Schimert. G., and kreatbaich, W.: Chnicil ‘experience with an implantable pacemaker, Ann. New York Acad. SC. 111:1075, 1964. 5. Zoll, P. M., Frank, H. A., and Linenthal, A. J.: Implantable cardiac pacemakers, Ann. New York Acad. SC. 111:1068, 1964. 6. Elmqvist, R., Landegren, J., Pettersson, S. O., Senning, A., and William-Olsson, G. : Artificial pacemaker for treatment of Adams-Stokes syndrome and slow heart rate, AM. HEART J. 65731, 1963. 7. Lagergren, H., and Johansson, L.: Intracardial stimulation for complete heart block, Acta Chir. Scandinav. 125562, 1963.
to electrical
diagnosis
of pacemaker
failure
E. Dekker, M.D.* J. Biiller, M.D. 21. M. Schuilenburg, M.D. Amsterdam, Netherlands
T
he electronic pacemakers used in the therapy of atrioventricular block are still far from perfect. With a considerable percentage of them, we must face the sometimes grave emergencies in patients returning with pacemaker failure. Proper treatment of this condition is based on the correct diagnosis of its cause. However, a complete set of diagnostic rules for the analysis of pacemaker failure is not yet available. Only a very few studies’J have concentrated on this subject. It is the purpose of this paper to present experience with a few diagnostic methods which have proved to be helpful in solving some of the electronic riddles of this new syndrome. These will be presented in a systematic form, followed by some summaries of cases in patients during treatment of whom this system gradually evolved. Methods
1. Prefailure documentation of the pacemaker function. Analysis of pacemaker failure is greatly facilitated by comparing the postfailure clinical and electrical symptoms with records of the prefailure function. Pacemaker failure is frequent enough to warrant documentation of the prefailure status in every case. This applies both to the function of the pacemaker proper and to the patient-pacemaker combination. From the Department of Cardiology and Received for publication Jan. 18, 1965. *Address: Afdeling Cardiologie en Klinische
739
Clinical Fysiologie,
A.
DOCUMENTATION
OF
PACEMAKER
FUNC-
Before connection of a new pacemaker to a patient its behavior in vitro, by means of an oscilloscope and a series of load resistances, which can be selected by means of a multipolar switch, is tested. Rleasurement of the voltage over each resistor will at the same time allow calculation of the current through it. The pulse rate of the pacemaker at each of these resistances should be noted. In some types of pacemakers the rate is dependent on the external load. In case of wire breakage this change in rate may prove to be helpful in diagnosis. TION.
B.
DOCUMENTATION
OF
FUNCTION
OF
THE
In the postoperative period the course of the wires over their full length and the position of the electrodes are documented for future reference by means of x-ray films. Furthermore, a standard electrocardiogram is obtained for the documentation of the direction and amplitude of the pacemaker artifacts. Proper attention is given to pacemaker rate after implantation, since a subsequent change in rate is an important sign of altered and probably disturbed function. In patients with disconnectable wires and external pacemakers the threshold and resistance of each wire are measured at least once in the postoperative period, by the PACEMAKER-PATIENT
Physiology, Wilhelmina
University Gasthuis,
COMBINATION.
of Amsterdam.
Amsterdam.
Amsterdam,
Netherlands.
Netherlands.
740
Dekker,
Bailer,
and Schuilenburg
methods discussed below, before the patient is discharged from the hospital. It is a considerable advantage of external pacemakers with internal electrodes that electrode resistance and threshold can be regularly checked. 2. Postfailwe analysis. The clinician should decide whether the cause of failure is localized in the pacemaker proper, in the wire-electrode combination, or in the patient’s heart. This decision is facilitated by the following methods: A. ELECTROCARDIOGRAPHY. The ECC; gives four types of information. It will record the rate, direction, and amplitude of the pacemaker artifacts and the form and behavior of the ventricular complexes. The pacemaker rate is compared to the prefailure rate. Any changes in rate should be interpreted in the light of the predetermined dependence of pacemaker rate on load resistance. Wire breakage usually causes higher resistance in the patient circuit because of the smaller surface of the broken wire. The direction and magnitude of the pacemaker artifacts is carefully compared to the prefailure record. A change in amplitude and direction of the pacemaker artifact is very suggestive of failure in the electrode-wire combination. The mechanism underlying this change is indicated in Fig. 1. The electrodes constitute an electrical dipole the vector of which changes its direction when the wire breaks. A large displacement of an electrode has a similar influence. The electrocardiogram also pro-
Fig. 1. Schematic diagram the pacemaker stimulus breakage of a pacemaker
of the electrical before (A) and wire.
vector of after (B)
.4m. Heart J. llrrrmber, 1965
vides a record of the behavior of the ventricular complexes. Each pacemaker artifact which falls outside the refractory period of spontaneous ventricular activity should be followed by a ventricular complex. Even a single instance of failure of the ventricle to follow the pacemaker should be viewed with the greatest suspicion. Therefore, long strips of record should be obtained and the effect of deep respiration and change of body position noted. Shortly after wire breakage it is common for the broken ends of the wire to maintain mechanical contact, except during special body positions or respiratory maneuvers. The QRS complexes may change their outline because the ventricles change from bipolar to unipolar stimulation (Fig. 2,A and B). B. ROENTGENOLOGY. The x-ray film may show a displacement of the wires and electrodes. If superposition of wire shadows is avoided, it may also show the localization of wire breakage. However, it should be stressed that the x-ray films must be of an optimal quality, and that a site of breakage may easily be overlooked unless the entire course of the wires is very patiently scrutinized. C. CONSTRUCTION OF ISOPOTENTIAL LINES OF THE PACEMAKERARTIFAcTON THE TRUNK.
This procedure may give useful information about the site of wire breakage and the polarity of the broken wire. Exploration with a precordial electrode to find the locus of all points at which the pacemaker artifact is zero establishes the approximate “zero” voltage line. Then isopotential lines can be mapped out by using a bipolar lead, say Lead I. The “right arm” electrode is fixed at an arbitrary site on the trunk, and the “left arm” electrode is moved around until once more the locus of all the sites at which the pacemaker artifact shows zero potential with respect to the “right arm” electrode is found. The result of this mapping is a series of more or less concentric curves surrounding sites of maximal positivity and negativity (Fig. 3). Directwriting electrocardiographs have such a low-frequency response as to pass only a small proportion of the voltage of the pacemaker artifact. Therefore, mapping of the isopotential lines is preferably done with the aid of an oscilloscope. It follows
Aids to electrical diagnosis
of @acemaker failure
741
Fig. 2. Electrocardiograms Leads I, II, and III from Patient D in the early postoperative period (A), after breakage of a wire (B), and after grounding of this wire and breakage of the second wire (C). Direction and amplitude of the pacemaker artifacts are changed in B and C. The artifact-artifact (au) interva1 is shorter in B and C.
Fig. 3. Mapping of isopotential lines on the trunk of Patient D after the first wire breakage ping of the insulation from the positive wire near the pacemaker and breakage of the second through the diaphragm (B).
(A ), and after stripwire near its passage
742
Dekker,
from the concept of the voltage distribution of an electrical dipole in a conducting rnedium that the zero line should be approximately at right angles to the electrical dipole constituted by the electrodes or wire ends. Furthermore, some relationship exists between the site and polarity of the voltage maxima on the surface and the spatial site of the poles of the dipole. The sites of maximal positive and negative voltage, therefore, aid in the roentgenologic localization of the wire breakage. If the relative position of the two poles has been identified roentgenologically, it is often easy to tell from the combination with the pattern of the isopotential lines whether the positive or the negative wire is broken. This clinical application of the isopotential lines will be exemplified below. D. AND
DETERMINATION RESISTANCES
OF OF
Am. Heart 1. December. 1965
an.d Schuilenburg
Biiller,
THE
THE
THRESHOLL)
WIRE-ELECTRODES.
If no fault can be found by this exploration of the electrode-wire combination, a high stimulation threshold of the myocardium should be excluded as a cause of failure. This is done simultaneously with the determination of wire-electrode resistance. In patients with implanted pacemakers it is generally necessary to interrupt the continuity of the skin in some way in order to establish an electrical contact with the wire. If the pacemaker pocket is opened during this procedure, the wires can be separated from the pacemaker, and each wire is then individually tested against an indifferent electrode, for example, a subcutaneous needle. (Jnder aseptic precautions the electrodewire to be tested is connected to an external pacemaker with a continuously adjustable output current. This current is measured by means of the voltage appearing over a resistor of known magnitude placed in series with the wire to be tested. If this voltage is measured on a dual-trace oscilloscope screen simultaneously with the voltage appearing between the electrode-wire and the indifferent electrode, the total resistance of these electrodes and the patient can be calculated. The Medtronics implanted pacemaker384 has a special provision for this measurement. The stimulating current is varied in order to find the threshold level for each electrode. If during the same session the implanted pacemaker is con-
netted by sterile electrical wires to the same series of load resistors used in preoperative control, its response can be measured and compared with preoperative performance. 3. Therapeutic measures. These are determined by the outcome of this analysis. A failing pacemaker is exchanged. If the threshold is increased, the pacemaker can sometimes be replaced by another type, if necessary by an external pacemaker, with higher output current. In the case of wire breakage or electrode displacement of one of a pair of myocardial electrodes, stimulation can be re-established by unipolar stimulation using an indifferent electrode. For this purpose the broken wire can be used if it is stripped of its insulation. This may be done near the pacemaker.5 In those types of pacemakers in which the polarit) of the wire cannot be recognized from the outside, determination of the polarit) through the intact insulation may be accomplished by a pole analyzer using the principle outlined in Fig. 4, in which the pacemaker with its wires is schematically represented. Current through the lvires induces a circular magnetic field in the direction indicated. If the current increases
0
* -. r;
-L +
Fig. 4. Schematic diagram of the pole analyzer. The pacemaker with its positive and negative electrode wires is indicated. Arrows indicate the circular magnetic field surrounding the turns of the coil. Mounted left and right below are oscilloscope pictures from the output signal from the coil when applied to a negative and a positive wire, respectively. A 1 ,OOO-ohm damping resistor is used
l’ohme Nzcmber
70 6
Aids LOelectrical diagnosis of pacemaker failure
743
Fig. 5. Practical construction of the pole analyzer. It consists of 520 turns of 0.20~mm. enameled copper wire on a Perspex core. Franz left to right: Aluminum cap for shielding the signal from interference emitted by the pacemaker proper, the pole analyzer applied to an electrode wire, and a diagram of the core construction.
during the rise time of the pacemaker pulse, a voltage spike is induced at the output of a coil held in close approximation to the wire. During the fall time of the pacemaker pulse a second spike is induced with opposite polarity. The practical construction of this simple device is illustrated in Fig. 5. Confusion is avoided by making the connections in such a way that during the actual preoperative identification a simple rule of thumb can be followed, whereby the first output spike should be positive if the coil is put around the positive wire in such a way that a letter P written on the coil points toward the pacemaker. Finally, if all wires are broken, or if their threshold has risen beyond the reach of pacemaker power, application of new electrodes, if necessary by a second thoracotomy, may become a necessity. Case summaries In PatientA, a 74-year-old man with a history of recurrent Stokes-Adams attacks and complete atrioventricular block, a Medtronics double wireelectrode was inserted on Sept. 9, 1961, and connected to an external pacemaker. On Oct. 27, 1961, pacemaker failure occurred. Resistance measurement of the wires showed a normal value for the negative wire (100 ohms) and a high resistance of the positive wire (3,900 ohms). A subcutaneous
needle in the abdominal wall was used as an indifferent electrode, and unipolar pacing was resumed. On Nov. 20, 1961, it was found that the pacemaker artifacts disappeared from the electrocardiogram on deep inspiration. The resistance of the remaining myocardial electrode-wire was now found to be very high on deep inspiration. It was concluded that this second wire was also broken. A second thoracotomy was performed on Nov. 25, 1961, and four ElemaG electrodes were implanted and connected to an external pacemaker. This combination functioned well until the patient’s death from multiple myeloma on Nov. 25, 1963. woman, a Medtronics In PatientB, a 52-year-old internal pacemaker was implanted elsewhere on Oct. 21, 1962, because of complete atrioventricular block with repeated Stokes-Adams attacks. On March 29,1963, she was admitted to our department for evaluation of a complaint of vague trembling sensations in the abdominal wall at the pacemaker site. No special attention was paid at that time to the small amplitude of the pacemaker artifacts. On Aug. 2, 1963, the patient died suddenly at home. Postmortem examination revealed an intact wireelectrode system. Examination of the pacemaker, however, showed that the output current had dropped to very low values, and the conclusion was that failure of the pacemaker proper was responsible for the patient’s sudden death. Patient C, 50 years old, suffered from complete atrioventricular block with recurrent Stokes-Adams attacks. On March 23, 1962, four epicardial electrodes were implanted and connected to an Elema external pacemaker.6 The batteries were changed on July 4, 1962. In January, 1963, the pacemaker rate showed a gradual rise: this was corrected else-
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where by repeated readjustment of the rate controls. Unfortunately, too little attention was paid to this phenomenon. On Feb. 2, 1963, the patient died suddenly. At autopsy the wires were found to be intact, but two of the batteries were exhausted. Patient D, a male, had a history of repeated Stokes-Adams attacks caused by complete atrioventricular block. On July 5, 1963, an Electrodyne TII 14 internal pacemaker was implanted. On Jan. 10, 1964, the patient presented with the complaint that he had observed a rise in his pulse rate from 6.5 to 70 per minute. This observation was confirmed by comparison with the record made previously (Fig. 2,.1 and B). Besides, it was noted that the direction and amplitude of the pacemaker artifacts had changed. Although every pacemaker artifact was followed by a ventricular complex, a wire breakage was suspected. This could not be found on the initial x-ray films. Since the pacemaker had made a quarter turn under the influence of pressure from the waist belt, it was suspected that the breakage might be situated near the pacemaker. Mapping of the isopotential lines on the trunk (Fig. 3,.4) showed that the two voltage maxima were far from the pacemaker, thus making the assumption of breakage in its neighborhood very unlikely. The zero line and the isopotential lines surrounding the maxima were marked by copper wire, and on the x-ray frhn thus obtained (Fig. 6) the breakage
point was found to be near the positive maximum. It was clear from this x-ray film that the intact electrode was superior and to the left of the broken wire, and that, therefore, the broken wire must have a positive polarity. On Jan. 20, 1964, both wires were exposed near the pacemaker, and the positive wire was identified by means of the pole analyzer (Fig. 5). Continuity of the electrical circuit was re-established by “grounding” this wire in the surrounding tissues by removing the jnsulation over approximately 2 cm., after which the pacemaker performed satisfactorily. was renewed pacemaker On Jan. 27, 1964, there failure. The electrocardiogram showed a 2:l atrioventricular block and a renewed change in the direction and amplitude of the pacemaker artifacts (Fig. 2,C). The pattern of the isopotential lines was thoroughly changed. The center of maximal positivity was seen near the pacemaker, where the positive wire had been bared, and the maximal negativity was found near the heart (Fig. 3,B). The voltage maxima corresponded we!l with the location of these poles on the x-ray film (Fig. 7). On Feb. 5, 1964, another thoracotomy was performed and an internal Elema pacemaker \vas implanted with two functioning and two spare electrodes. Until now the patient is doing well. Patient E, a 75year-old man who had had several Stokes-Adams attacks, was given an Electrodyne TK 14 internal pacemaker on Oct. 18, 1963. On
Fig. 6. The zero line and some isopotential lines marked by copper wires ponc hng to Fig. 3,:1. Insert: The site of wire breakage (slightly retouched).
on the x-ray
film
of Patient
D, c:0*
l-es-
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become complete. An x-ray film made shortly before operative exploration showed that the intact wire electrode was displaced and had possibly slipped out of the myocardium. Indeed, after identification with the pole analyzer and grounding of the positive wire, the heart could no longer be stimulated from the negative electrode. Both wires were withdrawn. One proved to be broken near the electrode: the other was intact and must previously have lost contact with the myocardium. On March 2, 1964, a permanent intracavitary electrode? was introduced and connected to an implanted pacemaker. Patient F, a 74-year-old man, had also a history of repeated Stokes-Adams attacks and a complete atrioventricular block. On Dec. 18, 1963, an Electrodyne TR 14 pacemaker was implanted. On Jan. 17, 1964, the patient observed irregularity of his pulse beat. The pulse rate was 48 per minute. An electrocardiogram showed only occasional stimulation of the ventricles. The pacemaker rate was somewhat higher than shortly after the operation. The amplitude and direction of the pacemaker artifacts were changed. The x-ray films showed breakage of one of the two wires. Comparison of the x-ray findings with results of the mapping of the pacemaker isopotentials on the trunk led to the conclusion that the broken wire had a negative polarity. After exposure of the wires the negative wire was identified through the intact insulation by the method described above. Its grounding restored pacemaker function. Two days later the heart rate again fell to 40 per minute. The electrocardiogram showed that tota failure followed the pacemaker. The chest x-ray film showed that the second wire was also broken. An Elema pacemaker with two spare wires was implanted on Jan. 31, 1964. The patient is doing well up to the present time.
Discussion
Fig. 7. Zero lines and some isopotential lines marked by copper wires on the x-ray film (Jan. 27, 1964) of Patient D, corresponding to Fig. 3,B. Maximal positivity is found near the pacemaker, where the stripped positive wire is imbedded. The area of maximal negativity surrounds the end of the broken negative wire.
Feb. 11, 1964, a routine electrocardiogram showed intermittent failure of the pacemaker. Amplitude and direction of the pacemaker artifacts were changed and their frequency was slightly higher than that shortly after operation. A chest x-ray film showed that one of the wires was broken near the heart. Comparison of the radiologic findings with the pattern of the isopotential lines led to the conclusion that the polarity of the broken wire was positive. Preparations were made for the “grounding” of this broken wire. Meanwhile, pacemaker failure had
The ease of control of wire integrity in patients with internal electrodes attached to an external pacemaker is exemplified in Patient A, in whom measurement of resistances led to a diagnosis of wire breakage. In other similarly treated patients, not included in this series, high thresholds nornlal resistances, probwere found with ably pointing to the development of connective tissue around the electrodes. Connecting the pacemaker to a spare electrode forestalled failure. Failure to pay attention to the small voltage of the pacemaker artifacts and to the change in pacemaker rate, respectively, may have contributed substantially. to the death of our Patients B and C. The case summaries of Patients D, E, and F awareness of the reflect our increasing significance of changes in rate, in direction, and amplitude of the pacemaker artifacts
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and the use of the combined results of x-ray examination and mapping of the isopotential lines of the pacemaker artifact on the trunk of the patient. The broken wire was operatively exposed and correctly identified by the pole analyzer, and pacing was restored after “grounding” of the broken wire in Patients D and F. Therapeutic successwas of disappointingly short duration because of breakage of the second wire shortly after the first. No explanation is offered for the remarkable similarity in lifespan of a pair of implanted wires in these cases, but it is assumed that in other cases the second wire may remain intact for considerably longer periods. It is hoped that in such cases the methods outlined above may add to the lifespan both of the pacemaker system and the patient. Summary
Some aids to electrical diagnosis of pacemaker failure are described. These consist of careful preoperative appraisal of pacemaker function and immediate postoperative electrocardiographic recording of rate and form of the pacemaker artifacts, and of the postfailure comparison of these same features. Mapping the isopotential lines of the pacemaker artifacts on the patient’s trunk, in combination with x-ray analysis, aids in the localization of wire breakage and in the determination of the
polarity of the broken wire. Some therapeutic implications of this analysis are exemplified and discussed. We wishto expressour gratitude to Prof. Durrer for his helpand support,to Prof. Dr.
Dr. D. L. H. van der Tweel for his invaluable help in the early phases of our pacemaker troubles, and to Prof. Dr. B. G. Ziedses des Plantes and his staff for their contribution to Figs. 6 and 7. REFERENCES 1. Parsonnet, V., Gilbert, L., Zucker, I. R., and Asa, M. M.: Complications of the implanted pacemaker. A scheme for detection of the cause bf the defect and methods for correction, J. Thoracic & Cardiovas. Sure. 45:801. 1963. 2. Kantrowitz, A.: Implant~ble carhiac pacemakers, Ann. New York Acad. SC. 111:1049. 1964. 3. Chardack, W. M., Gage, A. A., and Greatbatch, W.: Correction of complete heart block by a self-contained and subcutaneously implanted pacemaker, 1. Thoracic & Cardiovas. Surg.._ &814, 1961.4. Chardack. W. M.. Frederico. A. 1.. Schimert. G., and kreatbaich, W.: Chnicil ‘experience with an implantable pacemaker, Ann. New York Acad. SC. 111:1075, 1964. 5. Zoll, P. M., Frank, H. A., and Linenthal, A. J.: Implantable cardiac pacemakers, Ann. New York Acad. SC. 111:1068, 1964. 6. Elmqvist, R., Landegren, J., Pettersson, S. O., Senning, A., and William-Olsson, G. : Artificial pacemaker for treatment of Adams-Stokes syndrome and slow heart rate, AM. HEART J. 65731, 1963. 7. Lagergren, H., and Johansson, L.: Intracardial stimulation for complete heart block, Acta Chir. Scandinav. 125562, 1963.