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Effect of ambulatory blood pressure monitoring on the diagnosis and cost of treatment for mild hypertension
Effect of ambulatory blood pressure monitoring on the diagnosis and cost of treatment for mild hypertension Detection of mild hypertension by a small number of casual blood pressures may be inaccurate for the determination of average blood pressure. Nonetheless, casual pressures remain the basis for the diagnosis and treatment of hypertensive patients. We compared casual and noninvasive ambulatory blood pressure monitoring in a consecutive series of 60 subjects evaluated for possible mild hypertension on the basis of casual pressures. Ambulatory blood pressure monitoring was performed on days of usual activity. Correlations between casual systolic and average ambulatory systolic pressures or casual diastolic and average ambulatory diastolic pressures were not significant. Nearly half of the subjects had average ambulatory systolic pressures <130 mm Hg. Sixty percent had average ambulatory diastolic pressures <65 mm Hg. Nearly 40% had both systolic and diastolic pressures less than those limits. A preliminary analysis of the effects of these results on the short-term cost of antihypertensive treatment was made, assuming that treatment could be withheld from those with average ambulatory pressures <130/85 mm Hg. This approach suggests that ambulatory blood pressure monitoring need not increase overall cost, if the results of this evaluation are used in the decision to treat. (AM HEART J 1988;116:1152.)
Lawrence R. Krakoff, MD, Howard Eison, MD, Robert Sander J. Leiman, and Steven Lev. New Yorlz, N.Y.
Screening populations for high blood pressure classifies a large fraction as having mild hypertension on the basis of a few measurements.’ Statistically this group is at risk for future cardiovascular disease.2 However, clinical trials of therapy for mild hypertension indicate that only a small percentage of patients benefit from active treatment.3 In general they are 50 years old or greater, have diastolic pressures of 95 mm Hg or more before treatment, and have a reduction in pressure during therapy.* A substantial number of those receiving placebo also had a fall in pressure during observation and low cardiovascular morbidity.*s5 Such results indicate the need for increased precision in early identification of those persons whose blood pressure is likely to remain elevated after the initial screening period, thereby separating them from those with lower average pressures for whom drug treatment might be delayed or withheld. In addition to repeated office or clinic observaFrom School
the Hypertension of Medicine,
Division, CUNY.
Reprint requests: Lawrence 1085, Mount Sinai Hospital, 10029-6574.
1152
Department
R. Krakoff, 1 Gustave
of Medicine,
MD, Hypertension L. Levy Place,
Mount Division, New York,
Sinai Box NY
H. Phillips,
MD, PhD,
tion, two methods have been suggested for improvement in the diagnosis of mild hypertension, home self-determined blood pressures,6 and noninvasive ambulatory blood pressure monitoring.? The latter method has been used in a prospective surveillance study of more than 1000 patients. The results suggest that it may improve prediction of long-term cardiovascular risk in hypertensive patients.* In this article we describe the pattern of noninvasive ambulatory blood pressure monitoring observed in a series of adults referred for confirmation of the initial diagnosis of mild hypertension. In addition, estimates are provided for the impact of these results on short-term costs of health care, assuming that the results might be used in the decision to treat with antihypertensive medications. METHODS
Noninvasive ambulatory blood pressuremonitoring was used to evaluate a consecutive series of 60 adults (age range, 18 to 68 years old) referred for managementof mild hypertension detected on two or more occasionsby their initiai physician or screeningsite. All were originally given a diagnosisof hypertension and advised to begin antihypertensive medications. Ambulatory blood pressuremonitoring wasperformed either before treatment or at least 2 months after its withdrawal. None of the subjects had
Volume
116
Number
4
Benefit and cost EFFECT OF AMBULATORY
MONITORING
of
monitoring
1153
ON COST
500
100 1
2
0
TREAT
UL
4
3 YENS +
UONFTOR
AND
5
TEAT
Fig. 1. Comparison of cumulative cost for treatment of all subjects labeled as mild hypertensive to cost for initial ambulatory blood pressure monitoring and treatment of those persons whose blood pressure s-=130/85 mm Hg (60%). Results are expressed as percentage of cumulative costs at the end of each year of treatment.
evidence of secondary hypertension or cardiac, neurologic, renal, or peripheral vascular disease by usual clinical assessment. Ambulatory blood pressure recordings were performed on a day of typical activity for each subject. Either the Spacelabs 5200 device or Oxford/Suntek accutracker was used. Blood pressure measurements were made every 20 to 30 minutes from 600 AM to midnight and every 60 minutes from midnight to 690 AM. After transmittal to an IBM-
XT, data were processed with Lotus l-2-3 software. Device errors and blood pressure readings with a pulse pressureof <15 mm Hg were deleted automatically. An average of 38 + 14 (mean + SD) readings was available for analysis after error deletion. Average systolic and diastolic arterial pressures and standard deviations were
calculated. RESULTS
Comparison between average pressures and results of ambulatory blood pressure monitoring is shown in Table I. For the entire group, average ambulatory systolic and diatolic pressures were significantly lower than casual pressures. Forty-five percent of subjects had average ambulatory systolic pressures 430 mm Hg, 60% had average diastolic pressures 45 mm Hg, and 38% had average systolic and diastolic pressures <130/85. Correlations between casual and average ambulatory pressures were not significant (systolic, r = 0.136, and diastolic, r = 0.219). Effect on cost. Calculation of the cost for treatBlood
pressures.
casual blood
Table
I. Early
hypertension
study (60 subjects) Mean
Age (yr) Casual systolic pressure Casual diastolic pressure Ambulatory systolic pressure Ambulatory diastolic pressure
‘p <
0.01
compared
with
casual
pressures
36
by paired
k SD 11
155 100
18 9
131* 82*
11 9
t test.
ment of mild
hypertension after a two-stage clinic screening process has previously been made with a comprehensive economic model.$ Results of ambulatory blood pressure monitoring might have an impact on cost in several ways. If the information obtained was not used in the decision to treat patients, then cost would invariably increase by the price for the procedure. However, using the results
as the basis of whom to treat might eventually
lead We found that nearly two of five subjects (38 % ) initially labeled as hypertensive had average ambulatory pressures low enough to permit observation without drug treatment. In this case the cost of the test would be offset by the lack of cost for treatment of those subjects having lower blood pressures. If the cost of ambulatory blood pressure monitoring was equal to the yearly cost of treatment for hypertension, use of the procedure to reduce the fraction of to a substantial reduction in cost for treatment.
1154
Krakoff et al.
those treated from 100% to 60 % would increase overall cost to 160% for the first year. However, the cumulative cost for initial monitoring and then treating this fraction for the following years would diminish relative to the cumulative cost of treating all those labeled as hypertensive without monitoring. This pattern is shown in Fig. 1 and indicates that for a treatment period of 3 or more years, cumulative cost is lower for a group that is monitored initially and treated compared with a group not monitored.
American
October 1908 Heart Journal
of ambulatory blood pressure monitoring in the management of hypertensive patients cannot be made. However, these initial observations suggest that ambulatory blood pressure monitoring need not invariably increase the cost of care for mild hypertension. This new technique may direct antihypertensive therapy to those with higher average pressures. Aggressive treatment of this group might be more effective in achieving a reduction in long-term cardiovascular morbidity than has yet been demonstrated in clinical trials.
DISCUSSION
The large percentage of those persons initially labeled as having mild hypertension but with average pressures far below the usual lower limit of the hypertensive range that we have found by ambulatory monitoring, 38%) agrees with two prior reports.lo~ll We chose a dividing line of 130/85 mm Hg for ambulatory monitoring for two reasons. First, we have found that average systolic pressures <130 mm Hg and diastolic pressures <85 mm Hg are statistically (p CY< 0.01) below the usual clinic standard, 140/90 mm Hg.12 Second, Doppler/echocardiography studies suggest that left ventricular filling abnormalities and left ventricular hypertrophy are rare when average ambulatory pressures are below this level.13 Using information derived from ambulatory blood pressure monitoring of patients with mild hypertension, we have found that nearly 40% of subjects have pressures low enough for withholding antihypertensive treatment; a projection for the effect of this decision on relative cost over a short period has been made. This simplified approach omits many factors requiring investigation. Should patients who are found to be normotensive by ambulatory blood pressure monitoring initially be remonitored? If so, how often? How many will have increased blood pressure and require treatment? Should treated patients have ambulatory blood pressure monitoring as a guide to their therapy? Will this lead to improved control of their pressure and reduce future cardiovascular morbidity? Until information on these issues is available, calculation of overall costs and assessment of genuine benefit for long-term use
REFERENCES
1. Hypertension Detection and Follow-up Program Cooperative Group. Variability of blood pressure and the results of screening in the hypertension detection and follow-up program. J Chronic Dis 1978;31:651-68. 2. Rabkin SW, Matthewson AL, Tate RB. Predicting risk of ischemic heart disease and cerebrovascular disease from systolic and diastolic blood pressures. Ann Intern Med 1978;88:342-5. 3. MacMahon SW, Cutler JA, Furberg CD, Payne GH. The effects of drug treatment for hypertension on morbidity and mortality from cardiovascular disease: a review of randomized clinical trials. Prog Cardiovasc Dis 1986;24(suppl 1):99118. 4. Report by the Management Committee. The Australian therapeutic trial in mild hypertension. Lancet 198O;l: 1261-7. 5. Medical Research Council Working Party. MRC trial of treatment of mild hypertension: principal results. Br Med J 1985;291:97-104. 6. Rademacher M, Lindsay A, McLaren JA, Padfield PL. Home monitoring of blood pressure: usefulness as a predictor of nersistent hvnertension. Scot Med J 1987:32:16-g. 7. Pickering TG, Harshfield GA, Devereaux RB, Laragh JH. What is the role of ambulatory blood pressure monitoring in the management of hypertensive patients. Hypertension 1985;7:171-7. 8. Perloff D, Sokolow M, Cowan R. The prognostic value of ambulatory blood pressures. JAMA 1983;249:2792-8. 9. Stason W. Economics in hypertension management: cost and quality trade-offs. J Hype-rtens 1987;5:S55-9. 10. Horan MJ. Kennedv HL. Padeett NE. Do borderline hvnertensive patients ha;e labile b&d pressure? Ann 1ntern”Med 1981;94:466-8. 11. Drayer JI, Weber MA, Nakamura DK. Automated ambulatory blood pressure monitoring: a study in age matched normotensive and hypertensive men. AM HEART J 1985;109: 1334-8. 12. Phillips RA, Thornton J, Krakoff LR. Statistical considerations in ambulatory blood pressure recording. Clin Res 1987;35:358A. 13. Phillips RA, Eison HA, Buyun Y, Krakoff LR, Goldman ME. What level of blood pressure causes hypertensive heart disease? Clin Res 1987;35:447A.
Lawrence R. Krakoff, MD, Howard Eison, MD, Robert Sander J. Leiman, and Steven Lev. New Yorlz, N.Y.
Screening populations for high blood pressure classifies a large fraction as having mild hypertension on the basis of a few measurements.’ Statistically this group is at risk for future cardiovascular disease.2 However, clinical trials of therapy for mild hypertension indicate that only a small percentage of patients benefit from active treatment.3 In general they are 50 years old or greater, have diastolic pressures of 95 mm Hg or more before treatment, and have a reduction in pressure during therapy.* A substantial number of those receiving placebo also had a fall in pressure during observation and low cardiovascular morbidity.*s5 Such results indicate the need for increased precision in early identification of those persons whose blood pressure is likely to remain elevated after the initial screening period, thereby separating them from those with lower average pressures for whom drug treatment might be delayed or withheld. In addition to repeated office or clinic observaFrom School
the Hypertension of Medicine,
Division, CUNY.
Reprint requests: Lawrence 1085, Mount Sinai Hospital, 10029-6574.
1152
Department
R. Krakoff, 1 Gustave
of Medicine,
MD, Hypertension L. Levy Place,
Mount Division, New York,
Sinai Box NY
H. Phillips,
MD, PhD,
tion, two methods have been suggested for improvement in the diagnosis of mild hypertension, home self-determined blood pressures,6 and noninvasive ambulatory blood pressure monitoring.? The latter method has been used in a prospective surveillance study of more than 1000 patients. The results suggest that it may improve prediction of long-term cardiovascular risk in hypertensive patients.* In this article we describe the pattern of noninvasive ambulatory blood pressure monitoring observed in a series of adults referred for confirmation of the initial diagnosis of mild hypertension. In addition, estimates are provided for the impact of these results on short-term costs of health care, assuming that the results might be used in the decision to treat with antihypertensive medications. METHODS
Noninvasive ambulatory blood pressuremonitoring was used to evaluate a consecutive series of 60 adults (age range, 18 to 68 years old) referred for managementof mild hypertension detected on two or more occasionsby their initiai physician or screeningsite. All were originally given a diagnosisof hypertension and advised to begin antihypertensive medications. Ambulatory blood pressuremonitoring wasperformed either before treatment or at least 2 months after its withdrawal. None of the subjects had
Volume
116
Number
4
Benefit and cost EFFECT OF AMBULATORY
MONITORING
of
monitoring
1153
ON COST
500
100 1
2
0
TREAT
UL
4
3 YENS +
UONFTOR
AND
5
TEAT
Fig. 1. Comparison of cumulative cost for treatment of all subjects labeled as mild hypertensive to cost for initial ambulatory blood pressure monitoring and treatment of those persons whose blood pressure s-=130/85 mm Hg (60%). Results are expressed as percentage of cumulative costs at the end of each year of treatment.
evidence of secondary hypertension or cardiac, neurologic, renal, or peripheral vascular disease by usual clinical assessment. Ambulatory blood pressure recordings were performed on a day of typical activity for each subject. Either the Spacelabs 5200 device or Oxford/Suntek accutracker was used. Blood pressure measurements were made every 20 to 30 minutes from 600 AM to midnight and every 60 minutes from midnight to 690 AM. After transmittal to an IBM-
XT, data were processed with Lotus l-2-3 software. Device errors and blood pressure readings with a pulse pressureof <15 mm Hg were deleted automatically. An average of 38 + 14 (mean + SD) readings was available for analysis after error deletion. Average systolic and diastolic arterial pressures and standard deviations were
calculated. RESULTS
Comparison between average pressures and results of ambulatory blood pressure monitoring is shown in Table I. For the entire group, average ambulatory systolic and diatolic pressures were significantly lower than casual pressures. Forty-five percent of subjects had average ambulatory systolic pressures 430 mm Hg, 60% had average diastolic pressures 45 mm Hg, and 38% had average systolic and diastolic pressures <130/85. Correlations between casual and average ambulatory pressures were not significant (systolic, r = 0.136, and diastolic, r = 0.219). Effect on cost. Calculation of the cost for treatBlood
pressures.
casual blood
Table
I. Early
hypertension
study (60 subjects) Mean
Age (yr) Casual systolic pressure Casual diastolic pressure Ambulatory systolic pressure Ambulatory diastolic pressure
‘p <
0.01
compared
with
casual
pressures
36
by paired
k SD 11
155 100
18 9
131* 82*
11 9
t test.
ment of mild
hypertension after a two-stage clinic screening process has previously been made with a comprehensive economic model.$ Results of ambulatory blood pressure monitoring might have an impact on cost in several ways. If the information obtained was not used in the decision to treat patients, then cost would invariably increase by the price for the procedure. However, using the results
as the basis of whom to treat might eventually
lead We found that nearly two of five subjects (38 % ) initially labeled as hypertensive had average ambulatory pressures low enough to permit observation without drug treatment. In this case the cost of the test would be offset by the lack of cost for treatment of those subjects having lower blood pressures. If the cost of ambulatory blood pressure monitoring was equal to the yearly cost of treatment for hypertension, use of the procedure to reduce the fraction of to a substantial reduction in cost for treatment.
1154
Krakoff et al.
those treated from 100% to 60 % would increase overall cost to 160% for the first year. However, the cumulative cost for initial monitoring and then treating this fraction for the following years would diminish relative to the cumulative cost of treating all those labeled as hypertensive without monitoring. This pattern is shown in Fig. 1 and indicates that for a treatment period of 3 or more years, cumulative cost is lower for a group that is monitored initially and treated compared with a group not monitored.
American
October 1908 Heart Journal
of ambulatory blood pressure monitoring in the management of hypertensive patients cannot be made. However, these initial observations suggest that ambulatory blood pressure monitoring need not invariably increase the cost of care for mild hypertension. This new technique may direct antihypertensive therapy to those with higher average pressures. Aggressive treatment of this group might be more effective in achieving a reduction in long-term cardiovascular morbidity than has yet been demonstrated in clinical trials.
DISCUSSION
The large percentage of those persons initially labeled as having mild hypertension but with average pressures far below the usual lower limit of the hypertensive range that we have found by ambulatory monitoring, 38%) agrees with two prior reports.lo~ll We chose a dividing line of 130/85 mm Hg for ambulatory monitoring for two reasons. First, we have found that average systolic pressures <130 mm Hg and diastolic pressures <85 mm Hg are statistically (p CY< 0.01) below the usual clinic standard, 140/90 mm Hg.12 Second, Doppler/echocardiography studies suggest that left ventricular filling abnormalities and left ventricular hypertrophy are rare when average ambulatory pressures are below this level.13 Using information derived from ambulatory blood pressure monitoring of patients with mild hypertension, we have found that nearly 40% of subjects have pressures low enough for withholding antihypertensive treatment; a projection for the effect of this decision on relative cost over a short period has been made. This simplified approach omits many factors requiring investigation. Should patients who are found to be normotensive by ambulatory blood pressure monitoring initially be remonitored? If so, how often? How many will have increased blood pressure and require treatment? Should treated patients have ambulatory blood pressure monitoring as a guide to their therapy? Will this lead to improved control of their pressure and reduce future cardiovascular morbidity? Until information on these issues is available, calculation of overall costs and assessment of genuine benefit for long-term use
REFERENCES
1. Hypertension Detection and Follow-up Program Cooperative Group. Variability of blood pressure and the results of screening in the hypertension detection and follow-up program. J Chronic Dis 1978;31:651-68. 2. Rabkin SW, Matthewson AL, Tate RB. Predicting risk of ischemic heart disease and cerebrovascular disease from systolic and diastolic blood pressures. Ann Intern Med 1978;88:342-5. 3. MacMahon SW, Cutler JA, Furberg CD, Payne GH. The effects of drug treatment for hypertension on morbidity and mortality from cardiovascular disease: a review of randomized clinical trials. Prog Cardiovasc Dis 1986;24(suppl 1):99118. 4. Report by the Management Committee. The Australian therapeutic trial in mild hypertension. Lancet 198O;l: 1261-7. 5. Medical Research Council Working Party. MRC trial of treatment of mild hypertension: principal results. Br Med J 1985;291:97-104. 6. Rademacher M, Lindsay A, McLaren JA, Padfield PL. Home monitoring of blood pressure: usefulness as a predictor of nersistent hvnertension. Scot Med J 1987:32:16-g. 7. Pickering TG, Harshfield GA, Devereaux RB, Laragh JH. What is the role of ambulatory blood pressure monitoring in the management of hypertensive patients. Hypertension 1985;7:171-7. 8. Perloff D, Sokolow M, Cowan R. The prognostic value of ambulatory blood pressures. JAMA 1983;249:2792-8. 9. Stason W. Economics in hypertension management: cost and quality trade-offs. J Hype-rtens 1987;5:S55-9. 10. Horan MJ. Kennedv HL. Padeett NE. Do borderline hvnertensive patients ha;e labile b&d pressure? Ann 1ntern”Med 1981;94:466-8. 11. Drayer JI, Weber MA, Nakamura DK. Automated ambulatory blood pressure monitoring: a study in age matched normotensive and hypertensive men. AM HEART J 1985;109: 1334-8. 12. Phillips RA, Thornton J, Krakoff LR. Statistical considerations in ambulatory blood pressure recording. Clin Res 1987;35:358A. 13. Phillips RA, Eison HA, Buyun Y, Krakoff LR, Goldman ME. What level of blood pressure causes hypertensive heart disease? Clin Res 1987;35:447A.