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USE OF A MAGNET WITH PROGRAMMABLE PACEMAKERS
405
CORRESPONDENCE USE OF A MAGNET WITH PROGRAMMABLE PACEMAKERS Sir,—I read with interest the case report of Drs Madsen and Andersen on pacemaker-induced tachycardia during transurethral resection of prostate, in which placing a magnet over programmable pacemakers was advised to reduce the pacing rate [1]. Unless the precise characteristics of the pacemaker are known, magnets should not be placed on programmable pacemakers when diathermy is being used, as electromagnetic interference from diathermy may cause random reprogramming of the pacemaker [2]. I am uncertain why a paced tachycardia was interpreted as a sign of inadequate anaesthesia. Care during manually assisted ventilation avoids hyperventilation as effectively as the use of a mechanical ventilator. Edinburgh REFERENCES 1. Madsen GM, Andersen C. Pacemaker-induced tachycardia during general anaesthesia: a case report. British Journal of Anaesthesia 1989; 63: 360-361. 2. Domino KB, Smith TC. Electrocautery-induced reprogramming of a pacemaker using a precordial magnet. Anesthesia and Analgesia 1983; 62: 609-612.
G. MADSEN C.ANDERSEN
Odense Sir,—We thank Dr David for his remarks on our case report. It is correct that magnets, placed over programmable pacemakers during periods of diathermy, may cause random reprogramming of the pacemaker [1]. The use of a magnet may be controversial. Both the actual circumstances and the
REFERENCES 1. Domino KB, Smith TC. Electrocautery-induced reprogramming of a pacemaker using a precordial magnet. Anesthesia and Analgesia 1983; 62: 609-612.
1s
I
I
FIG. 1. Recording of an "ECG" from apatient with Meta MV 1202 pacemaker (Diascope (S & W)). The thin arrows indicate pacemaker stimulations. Thick arrows indicate P-waves in normal sinus rhythm with broad QRS complexes.
Downloaded from http://bja.oxfordjournals.org/ at University of Winnipeg on August 27, 2015
D. A. DAVID
characteristics of the particular pacemaker must be taken into consideration. An example of a problem related to the use of magnets over pacemakers was described in a clinical report by Shapiro and colleagues [2]. A magnet was placed over a pacemaker, into which was programmed a threshold test "Vario". When this test programme was initiated by the magnet, the pacemaker produced 16 pulses at 100 beat min"1. However, during the second sequence the output was reduced successively to 0 V. If the threshold for stimulation is high, several beats may fall out. The pacemaker will repeat the test programme until the magnet is removed! The pacemaker (META MV 1202, Telectronics), which the patient in our case report had implanted, does not have the "Vario" function. This pacemaker, which registers the ventilatory minute volume, is supplied with a bipolar electrode for stimulation of the heart. Pacemakers with bipolar electrodes are less sensitive to interference compared with those with unipolar electrodes [3]. In this connection, it should be observed that the pacing stimulus derived from a bipolar electrode may be difficult to see on an ECG, because of its small size (fig. 1). On a diascope this may be even more difficult, because of either noise interference or varying location of the leads. In this way the registration of heart rate may claim greater interest compared with the configuration of the ECG—to those who are unfamiliar with this problem.
406 2. Shapiro WA, Roizen MF, Singleton MA, Morady F, Bainton CR, Gayner RL. Intraoperative pacemaker complications. Anesthesiology 1985; 63: 319-322. 3. Werner Irnich. Interference in pacemakers. Pace 1984; 7: 1021-1048.
Dr Brain is to be congratulated on his ingenious device; I anticipate a growing popularity for its use by anaesthetists and, no doubt, in emergency situations by medical technicians. R. BODMAN
Dartmouth, Nova Scotia REFERENCES 1. Brain AIJ. The laryngeal mask airway—A new concept in airway management. British Journal of Anaesthesia 1983; 55: 801-804. 2. Broderick PM, Webster NR, Nunn JF. The laryngeal mask airway. A study of 100 patients during spontaneous breathing. Anaesthesia 1989; 44: 238-241. 3. Leech BC. Pharyngeal bulb gasway: a new aid in cyclopropane anesthesia. Anesthesia and Analgesia 1937; 16: 22-25.
Sir—The Laryngeal Mask (LM) differs in important ways from the airway designed by Leech. First, the anatomical position is different. The Leech Pharyngeal Bulb Gasway formed a plug in the upper pharynx behind the back of the tongue, with its lower end just reaching the tip of the epiglottis. The LM lies much deeper, with its tip resting against the upper oesophageal sphincter, allowing sufficient room above it to permit tonsillectomy to be carried out. Second, there is a clear difference in function between the two devices. The Leech airway forms a seal around the perimeter of the pharynx, while the LM seal is made at right angles to this, around the perimeter of the larynx. The mask and glottic apertures are thus facing each other, permitting blind intubation of the trachea via the tube of the LM, or fibreopric inspection of the larynx or bronchial tree. Because the LM seals against the larynx, it is also possible to pass tubes orfibrcopticgastroscopes behind the LM without loss of seal or disturbing the airway. Regarding the materials which were available, rubber was the material used in the first LM prototypes I The commercial LM is made in silicone rubber because it withstands autoclaving. A. I. J. BRAIN
London
Downloaded from http://bja.oxfordjournals.org/ at University of Winnipeg on August 27, 2015
DEJA VU Sir,—Dr A. I. J. Brain has evidently caught the attention of anaesthetists in the U.K. with his description of the "Laryngeal Mask" [1]. Others have given it their blessing [2], and it appears likely to prove a useful addition to the anaesthetist's armamentarium. However, in common with many good ideas it is not altogether original. Dr B. C. Leech of Regina, Saskatchewan, described his "Pharyngeal Bulb Gasway" in 1937 [3]. The principle and purpose are the same as Dr Brain's, but Leech had to make do with the materials then available—metal and rubber—before the introduction of neuromuscular blocking drugs and plastics. He designed a round metal tube with a shape similar to the standard " Guedel" airway, with which we arc all familiar, but "the lower end expanded and guarded by two metal loops which prevent the epiglottis or other tissue from closing over the lower aperture; a large bulb of resilient soft rubber carefully shaped to the contours of the adult pharynx fits over the lower end of the tube." He described its use: "when good surgical anaesthesia has been induced and the jaw muscles fully relaxed, the face piece is discarded. With the tongue held gently forward by means of the tongue forceps, the gasway is introduced, tipfirst,and following the contour of the roof of the mouth, is placed gently in position back of the tongue. The tongue is then released, causing the gasway to fit snugly, but gently in place." Dr Harold Griffith, who was a contemporary and friend of Dr Leech's, commented "our attitude toward the use of an endotracheal tube for abdominal surgery is that an adequate and unobstructed airway must be obtained at all cost. If the patient breathes quietly and smoothly with the face mask, we use that method. If the mask will not fit properly we use the "Leech gasway ". If this method is not satisfactory we then use an endotracheal tube." Dr Deirdre Gillies, who has succeeded Dr Griffith at the Queen Elizabeth Hospital in Montreal, has two specimens of the " Leech gasway "; they are over 50 years old and the rubber is no longer "resilient and soft", but the purpose is clearly the same as Dr Brain's, to provide a gastight airway, without passing a tube through the cords.
BRITISH JOURNAL OF ANAESTHESIA
CORRESPONDENCE USE OF A MAGNET WITH PROGRAMMABLE PACEMAKERS Sir,—I read with interest the case report of Drs Madsen and Andersen on pacemaker-induced tachycardia during transurethral resection of prostate, in which placing a magnet over programmable pacemakers was advised to reduce the pacing rate [1]. Unless the precise characteristics of the pacemaker are known, magnets should not be placed on programmable pacemakers when diathermy is being used, as electromagnetic interference from diathermy may cause random reprogramming of the pacemaker [2]. I am uncertain why a paced tachycardia was interpreted as a sign of inadequate anaesthesia. Care during manually assisted ventilation avoids hyperventilation as effectively as the use of a mechanical ventilator. Edinburgh REFERENCES 1. Madsen GM, Andersen C. Pacemaker-induced tachycardia during general anaesthesia: a case report. British Journal of Anaesthesia 1989; 63: 360-361. 2. Domino KB, Smith TC. Electrocautery-induced reprogramming of a pacemaker using a precordial magnet. Anesthesia and Analgesia 1983; 62: 609-612.
G. MADSEN C.ANDERSEN
Odense Sir,—We thank Dr David for his remarks on our case report. It is correct that magnets, placed over programmable pacemakers during periods of diathermy, may cause random reprogramming of the pacemaker [1]. The use of a magnet may be controversial. Both the actual circumstances and the
REFERENCES 1. Domino KB, Smith TC. Electrocautery-induced reprogramming of a pacemaker using a precordial magnet. Anesthesia and Analgesia 1983; 62: 609-612.
1s
I
I
FIG. 1. Recording of an "ECG" from apatient with Meta MV 1202 pacemaker (Diascope (S & W)). The thin arrows indicate pacemaker stimulations. Thick arrows indicate P-waves in normal sinus rhythm with broad QRS complexes.
Downloaded from http://bja.oxfordjournals.org/ at University of Winnipeg on August 27, 2015
D. A. DAVID
characteristics of the particular pacemaker must be taken into consideration. An example of a problem related to the use of magnets over pacemakers was described in a clinical report by Shapiro and colleagues [2]. A magnet was placed over a pacemaker, into which was programmed a threshold test "Vario". When this test programme was initiated by the magnet, the pacemaker produced 16 pulses at 100 beat min"1. However, during the second sequence the output was reduced successively to 0 V. If the threshold for stimulation is high, several beats may fall out. The pacemaker will repeat the test programme until the magnet is removed! The pacemaker (META MV 1202, Telectronics), which the patient in our case report had implanted, does not have the "Vario" function. This pacemaker, which registers the ventilatory minute volume, is supplied with a bipolar electrode for stimulation of the heart. Pacemakers with bipolar electrodes are less sensitive to interference compared with those with unipolar electrodes [3]. In this connection, it should be observed that the pacing stimulus derived from a bipolar electrode may be difficult to see on an ECG, because of its small size (fig. 1). On a diascope this may be even more difficult, because of either noise interference or varying location of the leads. In this way the registration of heart rate may claim greater interest compared with the configuration of the ECG—to those who are unfamiliar with this problem.
406 2. Shapiro WA, Roizen MF, Singleton MA, Morady F, Bainton CR, Gayner RL. Intraoperative pacemaker complications. Anesthesiology 1985; 63: 319-322. 3. Werner Irnich. Interference in pacemakers. Pace 1984; 7: 1021-1048.
Dr Brain is to be congratulated on his ingenious device; I anticipate a growing popularity for its use by anaesthetists and, no doubt, in emergency situations by medical technicians. R. BODMAN
Dartmouth, Nova Scotia REFERENCES 1. Brain AIJ. The laryngeal mask airway—A new concept in airway management. British Journal of Anaesthesia 1983; 55: 801-804. 2. Broderick PM, Webster NR, Nunn JF. The laryngeal mask airway. A study of 100 patients during spontaneous breathing. Anaesthesia 1989; 44: 238-241. 3. Leech BC. Pharyngeal bulb gasway: a new aid in cyclopropane anesthesia. Anesthesia and Analgesia 1937; 16: 22-25.
Sir—The Laryngeal Mask (LM) differs in important ways from the airway designed by Leech. First, the anatomical position is different. The Leech Pharyngeal Bulb Gasway formed a plug in the upper pharynx behind the back of the tongue, with its lower end just reaching the tip of the epiglottis. The LM lies much deeper, with its tip resting against the upper oesophageal sphincter, allowing sufficient room above it to permit tonsillectomy to be carried out. Second, there is a clear difference in function between the two devices. The Leech airway forms a seal around the perimeter of the pharynx, while the LM seal is made at right angles to this, around the perimeter of the larynx. The mask and glottic apertures are thus facing each other, permitting blind intubation of the trachea via the tube of the LM, or fibreopric inspection of the larynx or bronchial tree. Because the LM seals against the larynx, it is also possible to pass tubes orfibrcopticgastroscopes behind the LM without loss of seal or disturbing the airway. Regarding the materials which were available, rubber was the material used in the first LM prototypes I The commercial LM is made in silicone rubber because it withstands autoclaving. A. I. J. BRAIN
London
Downloaded from http://bja.oxfordjournals.org/ at University of Winnipeg on August 27, 2015
DEJA VU Sir,—Dr A. I. J. Brain has evidently caught the attention of anaesthetists in the U.K. with his description of the "Laryngeal Mask" [1]. Others have given it their blessing [2], and it appears likely to prove a useful addition to the anaesthetist's armamentarium. However, in common with many good ideas it is not altogether original. Dr B. C. Leech of Regina, Saskatchewan, described his "Pharyngeal Bulb Gasway" in 1937 [3]. The principle and purpose are the same as Dr Brain's, but Leech had to make do with the materials then available—metal and rubber—before the introduction of neuromuscular blocking drugs and plastics. He designed a round metal tube with a shape similar to the standard " Guedel" airway, with which we arc all familiar, but "the lower end expanded and guarded by two metal loops which prevent the epiglottis or other tissue from closing over the lower aperture; a large bulb of resilient soft rubber carefully shaped to the contours of the adult pharynx fits over the lower end of the tube." He described its use: "when good surgical anaesthesia has been induced and the jaw muscles fully relaxed, the face piece is discarded. With the tongue held gently forward by means of the tongue forceps, the gasway is introduced, tipfirst,and following the contour of the roof of the mouth, is placed gently in position back of the tongue. The tongue is then released, causing the gasway to fit snugly, but gently in place." Dr Harold Griffith, who was a contemporary and friend of Dr Leech's, commented "our attitude toward the use of an endotracheal tube for abdominal surgery is that an adequate and unobstructed airway must be obtained at all cost. If the patient breathes quietly and smoothly with the face mask, we use that method. If the mask will not fit properly we use the "Leech gasway ". If this method is not satisfactory we then use an endotracheal tube." Dr Deirdre Gillies, who has succeeded Dr Griffith at the Queen Elizabeth Hospital in Montreal, has two specimens of the " Leech gasway "; they are over 50 years old and the rubber is no longer "resilient and soft", but the purpose is clearly the same as Dr Brain's, to provide a gastight airway, without passing a tube through the cords.
BRITISH JOURNAL OF ANAESTHESIA