International 0
1991
Journal of Cardiology,
445
33 (1991) 445-446
Elsevier Science Publishers B.V. All rights reserved 0167-5273/91/$03.50
CARD10 13618
Clinical validation of four solid state ambulatory monitoring devices in detecting shift of the ST segment Kishor Phadke, David Mulcahy and Kim Fox Royal Brompton
and National
Heart Hospital, London,
U.K.
(Received 19 April 1991; revision accepted 10 June 1991)
Continuous monitoring for detection of changes in the ST segment during daily life in patients with stable angina has received increasing attention in recent years. Various reports testify to its role in the detection of silent ischaemia, and its potential usefulness in stratification of risk [1,21. Frequency modulated recorders, using magnetic tape for recording with subsequent visual analysis, have been previously validated for the detection of such changes. Analysis, however, is time consuming, and is subject to technical faults due to the presence of moving parts. Several new solid state devices have become available in recent years which provide real-time automated analysis, and have theoretically ideal recording capabilities with frequency response down to 0.05 Hz and linear phase integrity which may be as good, or better than, tape based recorders. We compared each of four solid state devices with a previously validated frequency modulated recording device [31 in patients with angina in order to assess whether such devices correlate well in detecting changes in the ST segment.
Key words: Ambulatory
monitoring;
Solid state systems; Silent ischemia
Patients, Methods, and Results
39 patients with coronary arterial disease and stable angina were studied. All underwent 24 hour ambulatory monitoring of the ST segment using the Oxford Medilog MR-35 FM recorder, and simultaneous monitoring using one of four solid state devices, the Oxford Medilog 6000 FD (N = lo), Puritan Bennett PB-3000 (N = lo), Marquette Seer (N = 1 l), and Q-Med Monitor one (N = 8). Two leads, CM5 and a modified inferior lead were utilised. Split lead electrodes were
Correspondence to: D. Mulcahy, Royal Brompton and National Heart Hospital, Sydney Street, London SW3, U.K.
used in approximately half of the patients, with very closely applied electrodes in the remaining patients. Patients continued their routine activities during the monitoring period. Analysis of the tapes and the solid state recordings were performed independently by a technician (for frequency modulated recorder) and a physician (solid states). Standard definitions for ischaemic change were used [4]. For analysis of the solid state recordings, the 24-hour trend was incorporated, with confirmation of suspected ischaemic episodes by visual inspection of the full size electrocardiographic strips printed by the analyser if available. Table 1 summarises the results. The four solid state systems when their results were combined accurately detected 59 episodes of change in the ST segment which were detected on the frequency modulated‘ recordings. Ten episodes detected by the frequency modulated recorder were not detected by the particu-
446 TABLE 1 Solid state system
No. of patients
Episodes True positive
Marquette Seer Oxford 6000-FD Puritan Bennett (PB-3000) Q-Med (Monitor One) Total
False positive
False negative
li 10
16 16
4 3
3 2
10
18
5
4
8 39
9 59
1 13
1 10
True positive refers to episodes detected by the frequency modulated as well as the solid state device. False positive refers to episodes read positive by the solid state but not confirmed on the frequency modulated device. False negative refers to episodes detected by the frequency modulated but not by the solid state device.
lar solid state system uti&d, and the reverse was the case in a further 13 instances. Although there was some variation in the number of episodes recorded between the devices for individual patients, when the frequency modulated recording was positive for ischaemia, the solid state recorders were also positive in all bar one instance, suggesting that the solid state recorders had a very similar sensitivity for the detection of coronary arterial disease to that of the frequency modulated recording device. Of the negative recordings with the solid state devices, only one had ischaemia (1 episode) on the alternative device.
Comment
The major use of any system for monitoring the ST segment relates at this time to the detection of coronary arterial disease. There is little evidence that the precise quantification of ischaemia over a 24-hour period is of benefit. From this viewpoint it appears that solid state recording devices are as sensitive as the tried and trusted frequency modulated recorders in the detection of coronary arterial disease, although, as previously reported [4], the sensitivity is rather low. One of the major potential benefits of the solid state
devices from the clinical viewpoint is that it would be time saving for technical services. We found that for all devices, however, the accurate interpretation of results required careful analysis of trends and subsequent overviewing of the electrocardiographic print-outs. The concept of production of a full automated printout which simply requires signing may be flawed. When the solid state report is negative for change in the ST segment, however, (as it will be in the majority of patients with angina), further overview of the tracings appears unnecessary, and visual confirmation by trend appears adequate. Disadvantages of those solid state systems which we analysed relate to their inability to record for more than a defined period (24 hours) due to “memory limitation” [5]. This problem has been addressed in newer systems. Furthermore, systems that need to be “downloaded” within two to three days of recording may be impractical for use over weekends, and are unsuitable for return to the monitoring centre by post. Overall, solid state recording devices appear as sensitive as frequency modulated recording devices in the detection of coronary arterial disease. The benefit of saving time in use of technicians relates only to those cases where the solid state recording is negative for change in the ST segment.
References Quyyumi AA, Mockus L, Wright C, Fox KM. Morphology of ambulatory ST segment changes in patients with varying severity of coronary artery disease: investigation of the frequency of nocturnal ischaemia and coronary spasm. Br Heart J 1985;53:186-193. Deedwania PC, Carbajal EV. Silent ischemia during daily life is an independent predictor of mortality in stable angina. Circulation 1990;81:748-756. Balasubramanian V, Lahiri A, Green HL, Stott FD, Raftery EB. Ambulatory ST segment monitoring. Problems, pitfalls, solutions, and clinical application. Br Heart J 1980;44:419425. Mulcahy D, Keegan J, Sparrow J, Park A, Wright C, Fox KM. Ischemia in the ambulatory setting: the total ischemic burden: relation to exercise testing and investigative and therapeutic implications. J Am Coll Cardiol 1989;14:11661172. 5 Nabel EG, Barry J, Rocco MB et al. Variability of transient myocardial ischemia in ambulatory patients with coronary artery disease. Circulation 1988;78:60-67.
1991
Journal of Cardiology,
445
33 (1991) 445-446
Elsevier Science Publishers B.V. All rights reserved 0167-5273/91/$03.50
CARD10 13618
Clinical validation of four solid state ambulatory monitoring devices in detecting shift of the ST segment Kishor Phadke, David Mulcahy and Kim Fox Royal Brompton
and National
Heart Hospital, London,
U.K.
(Received 19 April 1991; revision accepted 10 June 1991)
Continuous monitoring for detection of changes in the ST segment during daily life in patients with stable angina has received increasing attention in recent years. Various reports testify to its role in the detection of silent ischaemia, and its potential usefulness in stratification of risk [1,21. Frequency modulated recorders, using magnetic tape for recording with subsequent visual analysis, have been previously validated for the detection of such changes. Analysis, however, is time consuming, and is subject to technical faults due to the presence of moving parts. Several new solid state devices have become available in recent years which provide real-time automated analysis, and have theoretically ideal recording capabilities with frequency response down to 0.05 Hz and linear phase integrity which may be as good, or better than, tape based recorders. We compared each of four solid state devices with a previously validated frequency modulated recording device [31 in patients with angina in order to assess whether such devices correlate well in detecting changes in the ST segment.
Key words: Ambulatory
monitoring;
Solid state systems; Silent ischemia
Patients, Methods, and Results
39 patients with coronary arterial disease and stable angina were studied. All underwent 24 hour ambulatory monitoring of the ST segment using the Oxford Medilog MR-35 FM recorder, and simultaneous monitoring using one of four solid state devices, the Oxford Medilog 6000 FD (N = lo), Puritan Bennett PB-3000 (N = lo), Marquette Seer (N = 1 l), and Q-Med Monitor one (N = 8). Two leads, CM5 and a modified inferior lead were utilised. Split lead electrodes were
Correspondence to: D. Mulcahy, Royal Brompton and National Heart Hospital, Sydney Street, London SW3, U.K.
used in approximately half of the patients, with very closely applied electrodes in the remaining patients. Patients continued their routine activities during the monitoring period. Analysis of the tapes and the solid state recordings were performed independently by a technician (for frequency modulated recorder) and a physician (solid states). Standard definitions for ischaemic change were used [4]. For analysis of the solid state recordings, the 24-hour trend was incorporated, with confirmation of suspected ischaemic episodes by visual inspection of the full size electrocardiographic strips printed by the analyser if available. Table 1 summarises the results. The four solid state systems when their results were combined accurately detected 59 episodes of change in the ST segment which were detected on the frequency modulated‘ recordings. Ten episodes detected by the frequency modulated recorder were not detected by the particu-
446 TABLE 1 Solid state system
No. of patients
Episodes True positive
Marquette Seer Oxford 6000-FD Puritan Bennett (PB-3000) Q-Med (Monitor One) Total
False positive
False negative
li 10
16 16
4 3
3 2
10
18
5
4
8 39
9 59
1 13
1 10
True positive refers to episodes detected by the frequency modulated as well as the solid state device. False positive refers to episodes read positive by the solid state but not confirmed on the frequency modulated device. False negative refers to episodes detected by the frequency modulated but not by the solid state device.
lar solid state system uti&d, and the reverse was the case in a further 13 instances. Although there was some variation in the number of episodes recorded between the devices for individual patients, when the frequency modulated recording was positive for ischaemia, the solid state recorders were also positive in all bar one instance, suggesting that the solid state recorders had a very similar sensitivity for the detection of coronary arterial disease to that of the frequency modulated recording device. Of the negative recordings with the solid state devices, only one had ischaemia (1 episode) on the alternative device.
Comment
The major use of any system for monitoring the ST segment relates at this time to the detection of coronary arterial disease. There is little evidence that the precise quantification of ischaemia over a 24-hour period is of benefit. From this viewpoint it appears that solid state recording devices are as sensitive as the tried and trusted frequency modulated recorders in the detection of coronary arterial disease, although, as previously reported [4], the sensitivity is rather low. One of the major potential benefits of the solid state
devices from the clinical viewpoint is that it would be time saving for technical services. We found that for all devices, however, the accurate interpretation of results required careful analysis of trends and subsequent overviewing of the electrocardiographic print-outs. The concept of production of a full automated printout which simply requires signing may be flawed. When the solid state report is negative for change in the ST segment, however, (as it will be in the majority of patients with angina), further overview of the tracings appears unnecessary, and visual confirmation by trend appears adequate. Disadvantages of those solid state systems which we analysed relate to their inability to record for more than a defined period (24 hours) due to “memory limitation” [5]. This problem has been addressed in newer systems. Furthermore, systems that need to be “downloaded” within two to three days of recording may be impractical for use over weekends, and are unsuitable for return to the monitoring centre by post. Overall, solid state recording devices appear as sensitive as frequency modulated recording devices in the detection of coronary arterial disease. The benefit of saving time in use of technicians relates only to those cases where the solid state recording is negative for change in the ST segment.
References Quyyumi AA, Mockus L, Wright C, Fox KM. Morphology of ambulatory ST segment changes in patients with varying severity of coronary artery disease: investigation of the frequency of nocturnal ischaemia and coronary spasm. Br Heart J 1985;53:186-193. Deedwania PC, Carbajal EV. Silent ischemia during daily life is an independent predictor of mortality in stable angina. Circulation 1990;81:748-756. Balasubramanian V, Lahiri A, Green HL, Stott FD, Raftery EB. Ambulatory ST segment monitoring. Problems, pitfalls, solutions, and clinical application. Br Heart J 1980;44:419425. Mulcahy D, Keegan J, Sparrow J, Park A, Wright C, Fox KM. Ischemia in the ambulatory setting: the total ischemic burden: relation to exercise testing and investigative and therapeutic implications. J Am Coll Cardiol 1989;14:11661172. 5 Nabel EG, Barry J, Rocco MB et al. Variability of transient myocardial ischemia in ambulatory patients with coronary artery disease. Circulation 1988;78:60-67.
