European Heart Journal Advance Access originally published online on June 28, 2007
European Heart Journal 2007 28(17):2064-2069; doi:10.1093/eurheartj/ehm223
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Electrocardiographic left ventricular hypertrophy in GUSTO IV ACS: an important risk marker of mortality in women
1 Canadian VIGOUR Centre Research Group, 214 Heritage Medical Research Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
2 Cleveland Clinic Foundation, Cleveland, OH, USA
3 Department of Medical Sciences, University of Uppsala, Uppsala, Sweden
4 Department of Cardiology, University of Uppsala, Uppsala, Sweden
Received 3 December 2006; revised 20 April 2007; accepted 10 May 2007; online publish-ahead-of-print 28 June 2007.
* Corresponding author. Tel: +1 780 492 9385; fax: +1 780 492 0613. E-mail address: cindy.westerhout{at}ualberta.ca
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Abstract |
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Aim: To examine the association of left ventricular hypertrophy (LVH) on admission electrocardiography with adverse outcomes in acute coronary syndrome (ACS) patients.
Methods and results: A total of 7443 non-ST-elevation ACS patients in Global Utilization of STrategies to Open occluded arteries (GUSTO) IV ACS trial had admission electrocardiograms analysed at a core laboratory. LVH [
20 mm Cornell voltage (LV voltage) (women) or 28 mm (men) plus strain patterns] was observed in 586 (7.9%) patients, and women accounted for 74%. LVH patients were also older and had more co-morbidities, ST-depression 0.5 mm, elevated C-reactive protein and N-terminal pro-brain naturetic peptide (NT-proBNP), and lower troponin T. Invasive procedures occurred less often in LVH patients (cardiac catheterization: 31 vs. 38%, P = 0.001; percutaneous coronary intervention: 12 vs. 20%, P < 0.001). Mortality was significantly higher in patients with LVH (30 day: 5 vs. 3%, P = 0.046; 1 year: 14 vs. 7%, P < 0.001), whereas 30 day myocardial infarction (MI) and death/MI did not differ. After baseline adjustment including NT-proBNP, LVH remained associated with increased hazard of 1 year mortality in women, but not in men [P-interaction = 0.033; women: adjusted hazard ratio (LVH vs. no LVH): 1.42 (1.04–1.94), P = 0.029].
Conclusion: Electrocardiographic-LVH identifies an important subset of ACS patients with a higher risk of long-term mortality, particularly among women. These novel findings highlight opportunities to improve treatment and outcome among similar ACS patients.
Key Words: Left ventricular hypertrophy • Mortality • Gender
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Introduction |
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Although increases in left ventricular (LV) mass can accommodate an increased afterload stress, it may ultimately prove harmful. At that point, left ventricular hypertrophy (LVH) can lead to deleterious cardiovascular effects such as ventricular dysfunction, impaired coronary perfusion, and disturbances in cardiac rhythm.1 LVH is also a strong precursor of adverse outcomes in a variety of populations ranging from the general population to those with cardiovascular diseases.2–4 Women with LVH, in particular, have a higher risk of mortality than their male equivalents.5,6
Despite recognized unfavourable influence of this condition across the spectrum of coronary artery disease (CAD), LVH is rarely discussed in the realm of acute coronary syndromes (ACS) or cited as a modulator of clinical outcomes in these patients. In a large cohort of non-ST-elevation (NSTE)-ACS patients enrolled in the Global Utilization of STrategies to Open occluded arteries (GUSTO) IV ACS trial, we examined the prevalence of LVH [as diagnosed on the admission electrocardiogram (ECG)] and hypothesised that LVH would play a role in the likelihood of adverse outcomes. The extent to which gender and/or N-terminal pro-brain naturetic peptide (NT-proBNP), a marker of haemodynamic stress, may modulate the relationship of LVH with outcomes was also explored.
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Methods |
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Patient population
Details of the design and primary results of the GUSTO IV ACS trial have been previously described.7,8 In brief, patients over the age of 21 years were eligible if they presented within 24 h after one or more episodes of ischaemic chest pain lasting at least 5 min. In addition, eligible patients had to have either elevated cardiac troponin T or I above the upper limit of normal according to the local quantitative or qualitative assays, or transient or persistent ST-segment depression (
0.5 mm) on the admission ECG not known to be pre-existing or not attributable to coexisting disorders (e.g. LVH). Patients were excluded if they had evidence of an acute ST-segment elevation myocardial infarction (MI) or new left bundle branch block, or if percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) was planned within 30 days after enrolment. Eligible patients were randomly assigned to abciximab (0.25 mg/kg bolus plus 0.125 µg/kg/min continuous infusion for 24 or 48 h) or placebo. All patients were to receive aspirin and either unfractionated or low-molecular-weight heparin. Other clinically indicated medications were used at the discretion of the treating physician.
The primary endpoint of the trial was all-cause death or MI at 30 days. All possible cases of MI were adjudicated by a clinical endpoint committee, which was unaware of the study treatment assignment. Secondary endpoints included 30 day and 1 year death.7
Electrocardiogram measurements
Admission ECGs were read independently at the core ECG laboratory at the Cleveland Clinic Foundation (Cleveland, OH, USA) by experienced readers blinded to clinical outcomes. ECG data were then managed and analysed at the University of Alberta (Edmonton, Alberta, Canada). Admission ECGs were available in 7443 (95.4%) of the 7800 patients enrolled in the trial. LVH was identified on the admission ECG defined according to two established criteria: (i) Cornell voltage criteria: the sum of the amplitude of the S-wave in V3 and R-wave in the aVL lead, 28 mm for men and 20 mm for women,9 and (ii) the presence of repolarization abnormalities (strain patterns) classified as 1 mm ST-segment depression in lead I and aVL or in v5 and v6, or T-wave inversion in lead I and aVL or in v5 and v6.10
Laboratory analyses
Details of the central laboratory analyses have been published.11 Briefly, venous blood samples were collected at the point of randomization, and centrifuged sera were stored at –20°C in aliquots and sent to a central laboratory at the University of Uppsala (Uppsala, Sweden) for the analysis of troponin T, C-reactive protein, and NT-proBNP. A third-generation assay on an Elecsys (Roche Diagnostics) analyser was used to measure the levels of troponin T with a detection limit of 0.01 µg/L. C-reactive protein levels were ascertained using a chemiluminescent enzyme-labelled immunometric assay (Immulite CRP, Diagnostic Product Corp.) with a detection level of 0.1 mg/L. NT-proBNP concentrations were measured with a sandwich immunoassay on an Elecsys 2010 (Roche Diagnostics) analyser with an analytical range of 20–35 000 ng/L and a coefficient of variation at 3.3% at a level of 209 ng/L and 3.0% at a level of 7431 ng/L. Serum creatinine was also measured, and creatinine clearance rate was calculated using the gender-specific Cockcroft and Gault equation.12
Statistical analysis
Baseline patient characteristics were presented as numbers and percentages for discrete variables, whereas medians and 25th and 75th percentiles were given for continuous variables. Differences within these baseline characteristics according to LVH were tested using the 
2 and Mann–Whitney U tests where appropriate.
We examined the association of LVH status and 30 day PCI and then adjusted for other baseline characteristics using multivariable logistic regression (using stepwise selection). Baseline characteristics were considered if its univariable association with 30 day PCI had a P-value < 0.25, and the final set of covariates included age, gender, histories of angina, MI, CHF, PCI and CABG, heart rate, troponin T (quartiles), and NT-proBNP (quartiles). Interactions among age, gender, and creatinine clearance were tested but did not achieve statistical significance.
The association between LVH and clinical outcomes was examined using Kaplan–Meier estimates and multivariable Cox proportional hazard regression (using stepwise selection). In addition to LVH, other covariates predicting 1 year mortality included age, diabetes, histories of CHF and MI, current smoker, heart rate, ST-depression (none, 0.5 mm, 1–1.5 mm, 2 mm), creatinine clearance (quartiles: 25th, 59.2; 50th, 77.8; 75th, 99.1 mL/min), NT-proBNP (quartiles: 25th, 230.5; 50th, 643.7; 75th, 1763 ng/L), and troponin T (quartiles: 25th, 0.01; 50th, 0.111; 75th, 0.452 ug/L).13 Interactions among age, gender, and creatinine clearance did not achieve statistical significance. The likelihood of PCI within 30 days (quintiles) and plausible interaction terms with LVH were also tested (i.e. gender and NT-proBNP). The resulting discriminatory power (adjusted for over-optimism via bootstrapping) was a c-index of 0.805 and an over-optimism factor of 0.01. All tests were two-tailed, and the conventional level of statistical significance (i.e. P < 0.05) was used.
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Patient characteristics
Of the 7443 patients with available baseline ECG data, LVH was diagnosed in 586 patients [7.9%, 95% confidence interval (CI): 7.3–8.5]. As shown in Table 1, patients with LVH were more often female and older than those without LVH. They were also more likely to have hypertension, diabetes mellitus, and a history of cardiovascular diseases including angina pectoris, MI, heart failure, and stroke, but less likely to be a current smoker. The use of medications such as ACE-inhibitors and calcium channel blockers within 1 week prior to randomization was higher in LVH patients, a pattern which continued during the index hospitalization.
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Although LVH patients were less likely to present with MI and to have positive quantitative or qualitative troponin I or T, they were more likely to have at least 0.5 mm of ST-segment depression, the second entry criterion of the GUSTO IV ACS trial, than those patients without LVH. This pattern was particularly evident in women with LVH (relative to those without LVH) (data not shown). Median heart rate was significantly higher in LVH patients, whereas renal function as indicated by creatinine clearance was significantly lower in LVH patients than in those without. Median values of C-reactive protein and NT-proBNP assessed in core laboratories were also significantly higher in LVH patients.
Invasive procedures
According to the trial protocol, cardiac catheterization was discouraged during or within 12 h following the completion of the study drug infusion, and patients with PCI or CABG planned within 30 days of randomization were excluded from the trial. Overall, cardiac catheterization occurred in 22.5% of patients within the first 7 days and in 37.0% by day 30. In both the short and long term, patients with LVH underwent fewer catheterizations than those without LVH [7 days: 23.0% (no LVH) vs. 16.4% (LVH), P < 0.001; 30 days: 37.6 vs. 30.9%, P = 0.001] (Figure 1). Similarly, LVH patients were less likely to undergo PCI [7 days: 11.3% (no LVH) vs. 4.8% (LVH), P < 0.001; 30 days: 20.1 vs. 11.9%, P < 0.001]. The likelihood of PCI within 30 days was associated with LVH [adjusted odds ratio (OR): 0.78, 95% CI 0.57–0.98, P = 0.035]. Rates of CABG, however, were not statistically different [7 days: 3.2% (no LVH) vs. 2.4% (LVH), P = 0.28; 30 days: 11.3 vs. 9.9%, P = 0.31].
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Clinical outcomes
Rates of 30 day MI and death/MI were similar regardless of LVH [30 day MI: 5.4% (no LVH) vs. 5.1% (LVH), P = 0.92; 30 day death/MI: 8.0% (no LVH) vs. 8.0% (LVH), P = 0.94]. Mortality, however, was significantly higher in LVH patients; 31% higher in LVH patients at 30 days and there was a two-fold increase at 1 year (Figure 2A). And higher rates of 1 year mortality were particularly evident in women with LVH (Figure 2B). After adjustment for various baseline characteristics and propensity for PCI, LVH did not remain a significant predictor of 30 day death or 1 year mortality [30 day mortality: adjusted hazard ratio (HR): 0.84 (0.56–1.26), P = 0.40; 1 year mortality: adjusted HR: 1.22 (0.95–1.56), P = 0.119]. However, a significant interaction between gender and LVH was observed such that LVH remained strongly associated with increased long-term mortality in women, but not in men (P-interaction = 0.033). Women with LVH had a more than 40% increase compared with those without LVH [adjusted HR: 1.42 (1.04–1.94), P = 0.029] (Figure 3). Notably, NT-proBNP was independently associated with 1 year mortality in both genders.
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Discussion |
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Traditionally, LVH has not been considered in the list of established risk factors in ACS patients.14–17 A unique opportunity to examine this was possible through the assessment of LVH on the admission ECG in the GUSTO IV ACS trial. In terms of invasive treatment, we found that patients with LVH were less likely to undergo invasive procedures such as cardiac catheterization and PCI within the first week and through to 30 days. LVH was also associated with an increased risk of 1 year mortality, particularly in women, and notably, was independent of NT-proBNP.
Comparisons with other studies
Treatment following an acute coronary event in LVH patients has not been well studied. Similar to our study, however, East et al.6 showed in a cohort of CAD patients undergoing catheterization that patients with LVH subsequently underwent fewer PCI and CABG procedures. Whether there are opportunities to enhance outcomes of such patients through the utilization of these procedures or other strategies such as more intensive secondary preventative pharmacotherapy is unclear. In our study, an increased likelihood for PCI within 30 days of the initial acute event translated into improved survival in the first year, independent of LVH, which would suggest that increased use of PCI in those with co-existent epicardial coronary disease may also improve their outcomes.
In contrast to its association with invasive therapy, the prognostic implications of LVH to the general population have received more attention. LVH was among the most significant predictors of cardiovascular morbidity and mortality in the general population, as demonstrated by the Framingham Heart Study.18 Not surprisingly, clinical trials of left ventricular dysfunction, hypertension, and heart failure patients also point to LVH as prominent contributor to adverse outcomes in long-term follow-up.5 To a lesser extent, the prognostic value of LVH has been recognized in CAD patients.6,19,20 For instance, East et al.'s study demonstrated that echocardiographic LVH was a significant predictor of long-term mortality after adjustment for other baseline characteristics. There is a dearth, however, in our understanding of the role of LVH in NSTE-ACS patients who do not undergo invasive study.
From the few studies conducted in ACS patients, the presence of LVH appears to confer significant risk of short- and long-term mortality. For instance, in angina patients presenting to the emergency department, a nearly seven-fold unadjusted relative risk of death within the first 48 h was observed in those with LVH.4 And in a cohort study of 4720 consecutive AMI patients treated in the coronary care unit in the early 1980s, the 1 year mortality rate was 19.7% in patients with LVH vs. 8.7% in those without (adjusted OR: 1.51, 95% CI 1.09–2.10).3
Elevation of brain natriuretic peptides, including NT-proBNP, is commonly observed in patients with heart failure, left ventricular dysfunction, and LVH.21,22 More recently, through our own work and others, the value of this biomarker has also been recognized in ACS patients.11,23,24 The novelty of the current study is the opportunity to examine the association between systematically collected NT-proBNP and ECG-diagnosed LVH in NSTE-ACS patients. It seems likely that neurohormonal elevation provides additional indication of left ventricular overload and/or stretch, thereby signalling worse future outcomes in both men and women.
Further interrogation of our findings, however, revealed a major and heretofore unreported difference in the role of gender, as it relates to the prognostic value of LVH in NSTE-ACS. Several studies of CAD-free populations have observed that women have a substantially higher prevalence of LVH and poorer prognosis than men.18,20,25 These findings were confirmed in our study of ACS patients, with women constituting 38% of the overall GUSTO IV ACS population, yet over 70% of LVH patients. These women had a 1 year mortality more than twice that of men with LVH [16.7% (women) vs. 7.7% (men), P = 0.006]. The underlying nature of their cardiac disease may help to explain, in part, this difference. Coronary perfusion and reserve are compromised in LVH patients, even in those with normal coronary arteries, owing to impaired dilation capacity as a result of structural changes and increased extrinsic coronary resistance.26,27 Women, in particular, tend to have greater increases in wall thickness and poorer dilation of the LV cavity, which compromises the ability to withstand wall stress and ischaemia.28 Conversely, the response to wall stress in men is not manifested in wall thickening or loss of dilation. The condition may be further exacerbated in women who have a higher likelihood for microvascular disease and normal coronary arteries, as previously suggested.7,29,30 Angiographic confirmation of microcirculatory disease in these female patients with LVH and elevated NT-proBNP in GUSTO IV ACS may have provided further insight into this issue.
The current study also highlights that LVH was more prevalent in older patients.
Data from the Framingham population and other studies have indicated that LV mass increased with age only in women,31 whereas more recent data from Olivetti et al.32 suggested that with ageing, LV mass was preserved in women, but not in men. In particular, their work showed that as men aged, the number of ventricular cardiac myocytes and the proportion of mononucleated and binucleated cells decreased and the size of myocytes increased.
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Limitations |
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Some limitations of our study should be noted. First, the ECG was used in the current study to diagnose LVH, a method that has some inherent weaknesses. While the ECG is often used in large-scale screening programmes, it has established lower sensitive than echocardiography, a higher standard of LV mass detection.33 Several validation studies have calculated the sensitivity of echocardiography to be in the range of 85–100%, whereas the sensitivity of ECG reached as high as 50% in high-risk cardiovascular disease patient populations and as low as 6–17% in population-based studies. The costs and feasibility associated with the performance of echocardiography, however, make it an impractical option compared with the ECG, which is a simple, universally available test at the point of patient entry. Although echocardiography might have further complemented our findings, we believe that the choice to use the gender-specific Cornell voltage criteria and strain patterns was well founded, as it has been shown to outperform other ECG criteria such as Sokolow–Lyon voltage and Romhilt–Estes point score.34
Additional refinement of our results may have been possible through patient attributes such as height (for body-surface area adjustment) and systolic blood pressure, which were not available in GUSTO IV ACS.
A final limitation relates to the usual issue of generalizability of these findings to the global ACS population. Although patients with ST-depression related to pre-existing disorders such as LVH were to be excluded from the GUSTO IV ACS trial, nearly 8% of enrolled patients were diagnosed with LVH on the admission ECG. Since the frequency of LVH in the overall general population is likely greater, our findings deserve exploration in broader patient groups.
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Conclusion |
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This study highlights the important association of LVH and long-term prognosis in the ACS patient population. These novel findings should encourage careful assessment of LVH in ACS patients, particularly in females. Investigators should also consider this issue when designing future trials and interrogating population-based registries.
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The GUSTO IV ACS trial was funded by Centocor (Malvern, PA, USA).
Conflict of interest: Research grant obtained from Centocor: L.W., S.J. Research grant from Eli Lilly and Centocor for P.W.A.
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