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(Hypertension. 2004;44:459.)
© 2004 American Heart Association, Inc.
Scientific Contributions |
From the Hypertension and Cardiovascular Rehabilitation Unit (R.H.F., J.A.S., L.T., H.C.), University of Leuven, Leuven, Belgium; Erasmus University (W.H.B.), Rotterdam, the Netherlands; Imperial College, Hammersmith Hospital (C.J.B.), London, UK; University of Maastricht (P.W.d.L.), Maastricht, the Netherlands; Istituto Auxologico Italiano (G.L.), Ospedale San Luca, Milano, Italy; National Public Health Institute and the University of Helsinki (C.S., J.T.), Helsinki, Finland; Clinical Pharmacology Unit (J.W.), Aberdeen Royal Infirmary, Aberdeen, UK; Department of Family Medicine (Y.Y.), Hadassah Medical School, Hebrew University of Jerusalem, Jerusalem, Israel.
Correspondence to R. Fagard, MD, PhD, Professor of Medicine, Hypertension and Cardiovascular Rehabilitation Unit, U.Z.Gasthuisberg-Hypertensie, Herestraat 49, B-3000 Leuven, Belgium. E-mail robert.fagard{at}uz.kuleuven.ac.be
| Abstract |
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0.01 for all). A 1-mV decrease in electrocardiographic voltages during follow-up independently predicted a lower incidence of cardiac events (relative hazard rate: 0.86; P
0.05), but not of stroke or mortality. In conclusion, electrocardiographic voltages at baseline and their serial changes during follow-up predict subsequent events in older patients with systolic hypertension.
Key Words: antihypertensive therapy elderly electrocardiography hypertension, essential hypertrophy, cardiac prognosis
| Introduction |
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| Methods |
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At each follow-up visit,15,16 BP was the average of 2 BP measurements in the sitting position, by use of standard sphygmomanometry. Baseline BP was the average of 2 BP at each of 3 visits. A standard 12-lead ECG was performed at baseline and yearly thereafter. As predefined in the protocol, investigators at the coordinating office measured the voltages of SV1, RaVL, and RV5 (mV). ECG LVM was defined as the sum of RaVL+SV1+RV517,18 and ECG-LVH as RaVL+SV1+RV5>4.7 mV.
All events that occurred during follow-up were corroborated by the Syst-Eur End Point Committee.15,16 Outcome variables were: (1) Fatal and nonfatal strokes. Stroke was defined as a neurological deficit with symptoms continuing for >24 hours or leading to death with no apparent cause other than vascular. (2) Fatal and nonfatal coronary heart disease, comprising acute myocardial infarction and sudden death. Myocardial infarction was defined as 2 of the following 3 disorders: typical chest pain, electrocardiographic changes, and increased cardiac enzymes. Sudden death included any death of unknown origin occurring immediately or within 24 hours of the onset of acute symptoms, as well as unattended death for which no likely cause could be established by necropsy or medical history. Angina pectoris and arrhythmias were not included, unless fatal. (3) Fatal and nonfatal heart failure, irrespective of hospitalization. The diagnosis required the presence of the following 3 disorders or symptoms: (a) dyspnea; (b) clinical signs (such as ankle edema or pulmonary crepitations); and (c) the necessity of treatment with diuretics, vasodilators or antihypertensive drugs. (4) All cardiac events comprise coronary heart disease and heart failure as defined. (5) All cardiovascular events comprise all strokes and all cardiac events as defined. (6) Cardiovascular mortality, including all fatal cardiovascular events. (7) All-cause mortality.
Statistical Analysis
Database management and statistical analysis were performed using SAS software, version 6.12 (SAS Institute Inc). Data are reported as mean±SD or as proportions. Comparisons between groups were performed by Student unpaired t tests or by
2 tests. The prognostic significance of baseline ECG voltages and ECG LVH was assessed by Cox regression analysis on patients in whom a baseline ECG was available, with exclusion of patients with previous myocardial infarction, left bundle branch block, or implanted artificial pacemaker. The prognostic value of serial changes in ECG voltages during follow-up was analyzed in patients with a baseline ECG and at least 1 follow-up ECG. In a first analysis, the change of ECG voltages from baseline was entered as a time-dependent covariate in Cox regression models.19 In this analysis, the likelihood of an event that occurred at time "t" depends on the value of the last available ECG before time "t" for all subjects still in follow-up at time "t." In a second analysis, we used the changes in ECG voltages from baseline to the last available ECG, which is the last ECG before the event in case of an event. In the analysis of baseline ECG, we adjusted for age, gender, body mass index, smoking, systolic BP, pulse rate, diabetes, and previous antihypertensive treatment and cardiovascular complications at baseline.15 In the analysis of ECG changes during follow-up, we also adjusted for baseline ECG voltages and concomitant systolic BP changes. In the combined analysis of the 2 study groups, we also adjusted for study group. In patients with >1 cardiovascular event, the first relevant event was considered in each of the analyses. Relative hazard rates reflect the risk associated with a 1-mV higher value of RaVL+SV1+RV5 or the presence of LVH at baseline, or a 1-mV decrease in ECG voltages during follow-up. A 2-tailed P
0.05 was considered significant.
| Results |
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Prognostic Significance of Baseline ECG Voltages
Median follow-up of the 4507 patients after randomization was 6.1 years (range, 0.1 to 13 years); total follow-up time was 28 743 patient-years. Table 2 summarizes the number of events and the relative hazard rates reflecting the risk associated with a 1-mV greater sum of RaVL+SV1+RV5. In the combined analysis of the 2 treatment groups, ECG voltages significantly and independently predicted total and cardiovascular mortality, all strokes, all cardiac events, coronary heart disease, heart failure, and aggregate fatal and nonfatal cardiovascular events (P
0.01). The relative hazard rate for sudden death was significant before (1.24; 95% confidence interval [CI], 1.05 to 1.45; P
0.05) but not after adjustment (1.16; 95% CI, 0.98 to 1.37). The adjusted relative risk of ECG LVH at baseline was 1.51 (95% CI, 1.20 to 1.91) and 1.72 (95% CI, 1.26 to 2.35) for, respectively, total and cardiovascular mortality (P
0.001), 1.68 (95% CI, 1.33 to 2.13) (P
0.001) for all cardiovascular events, and, respectively, 1.72 (95% CI, 1.17 to 2.52) (P
0.01) and 1.72 (95% CI, 1.30 to 2.28) (P
0.001) for strokes and cardiac events.
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Prognostic Significance of Changes in ECG Voltages During Follow-Up
A total of 22 412 follow-up ECG were recorded in the 4159 patients during the trial. Median follow-up after the first follow-up ECG was 5.1 years (range, 0.003 to 11.8 years) in the active treatment group and 5.1 years (range, 0.003 to 12.0 years) in the control group; total follow-up times were, respectively, 11 863 and 11 316 patient-years. Placebo treatment was gradually replaced by active therapy in the control group as more patients entered phase 2 of the trial. The Figure illustrates the changes in ECG voltages and in BP during follow-up. In multiple regression analysis, after adjustment for baseline ECG voltages, reductions in ECG voltages were more pronounced in the presence of greater decreases in systolic BP (P<0.05).
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Table 3 summarizes the results on the prognostic significance of changes in ECG voltages during follow-up when entered as a time-dependent variable. In both groups taken together, changes in ECG voltages predicted cardiac events independently of baseline ECG voltages and other covariates, including changes in systolic BP. A 1-mV decrease in ECG voltages was associated with a 14% reduction in all cardiac events and a 16% reduction in coronary heart disease risk (P
0.05). ECG changes during follow-up did not predict total mortality, cardiovascular mortality, sudden death or the incidence of stroke. In the analysis in which the last available ECG was used, the risk reduction in cardiac events and coronary heart disease amounted to, respectively, 17% and 21% (P
0.01) (Table 4).
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| Discussion |
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There is little doubt that ECHO LVH and ECG LVH are associated with increased incidence of cardiovascular events.17 ECG studies have used a variety of criteria to define LVH, usually including voltage measurements, but it is well known that the ECG has relatively low sensitivity for the detection of LVH. Furthermore, this approach does not consider the full quantitative range of ECG voltages. In the current study, we measured voltages in 3 leads reflecting potentials from the left ventricle. The sum of RaVL+SV1+RV5 predicted all-cause and cardiovascular mortality, stroke, cardiac events, and all cardiovascular events combined. A 1-mV higher value was associated with a 19% greater risk of a cardiovascular event, independent of important confounders including age, gender, and BP.
Whereas the prognostic significance of LVH is well accepted, there is less certainty on the independent prognostic power of regression of LVH or reductions in LVM. Several studies have used echocardiography to examine associations between categorical changes in LVH and outcome in patients with hypertension.911,13 All but one study11 reported significant relationships between such changes and various aggregates of cardiovascular events. These echocardiographic studies were usually retrospective, with small numbers of participants or few events. Two studies have been published on the prognostic implications of regression of ECG LVH. Levy et al8 included 524 men and women from the Framingham Heart Study, with ECG evidence of LVH, irrespective of BP. Subjects with a serial decline in ECG voltage quartile (RaVL+SV3) were at lower risk for cardiovascular disease, a composite of coronary heart disease, congestive heart failure, stroke, transient ischemic attack, and peripheral arterial disease, than those with no serial change. The associations persisted after adjustment for age, traditional risk factors, baseline quartile voltage and BP, and the accompanying serial change in systolic BP. Mathew et al12 analyzed the impact of changes in ECG markers of LVH in the HOPE trial, which recruited patients at high cardiovascular risk. ECG LVH was considered to be present if the sum of the S wave in V1, and the R wave in V5/V6 exceeded 3.5 mV. During follow-up, the primary outcome, a composite of cardiovascular death, myocardial infarction, and stroke, occurred in 12.3% of the 7539 patients with regression or prevention of LVH and in 15.8% of the 742 patients with development or persistence of LVH (P=0.006).
With regard to cause-specific cardiovascular disease, we observed that the prognostic value of baseline ECG voltages and changes during follow-up were consistent for coronary heart disease but not for stroke. This could mean that ECG LVM is a marker of overall risk for cardiovascular disease including stroke, but that the favorable effects of LVM regression only pertain to cardiac complications, possibly related to improved cardiac function, coronary flow reserve, and/or less arrhythmias. Another explanation could be that stroke is more powerfully related to BP and changes in BP than are cardiac events. Among previous studies, only Mathew et al12 reported on specific cardiovascular events and found that regression or prevention of ECG LVH was associated with a lower incidence of cardiac events in comparison with development or persistence of LVH, whereas there was only a nonsignificant trend for stroke.
In the current study, the regression of ECG LVM was achieved with nitrendipine-based antihypertensive therapy to which enalapril and hydrochlorothiazide could be added. Regression of ECHO LVM has been observed with all 3 drug classes.20 Dihydropyridine calcium channel blockers have been shown to be as effective in reducing LVM as other first-line agents in directly comparative studies.21,22
Strengths of the current study are the prospective design, the large sample size, the large number of events allowing cause-specific analyses, the blinded evaluation of the events by an End Point Committee, and the yearly recorded ECG. However, several limitations have to be considered. Because of the 198 centers involved in Eastern and Western Europe and the older study population, echocardiography was not included in the protocol of the trial. The quantitative ECG analysis was limited to the simple measurement of 3 predefined voltages, reflecting the left ventricle, as in the EWPHE trial conducted by the same investigators.23,24 In the current study and in previous reports,17,24 the sum of RaVL+SV1+RV5 was significantly related to systolic BP. In a post hoc analysis of 74 patients from a previous study of our group,25 in which ECHO LVM was measured in well-standardized conditions, the correlation coefficient of RaVL+SV1+RV5 with ECHO LVM was 0.43, and amounted to 0.46 when LVM was indexed for body surface area (P<0.001). Finally, the analysis on the prognostic significance of the follow-up ECG was limited to patients who had at least 1 ECG after randomization.
Perspectives
The current study supports the suggestion that regression of LVH/LVM can be considered a surrogate end point for morbid events in hypertension treatment trials.26 The relationship of LVH/LVM and of the changes of LVH/LVM with subsequent morbid events appears to be consistent. In the current study, we found that ECG voltages can be used as a quantitative variable, which is an advantage over categorical analyses, in which patients may remain in the same LVH category despite a relevant change in ECG LVM. Furthermore, electrocardiography is possible in all patients and is less costly and time-consuming than echocardiography. Whereas there is currently no strong evidence from directly comparative studies, that first-line agents differ in their effects on LVH/LVM, except perhaps for angiotensin II antagonists,27 quantitative electrocardiography can probably contribute to the assessment of the effects of newer drugs on LVH/LVM in large study groups.
| Acknowledgments |
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Received April 27, 2004; first decision May 12, 2004; accepted August 3, 2004.
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