The Differences of Left Ventricular Geometry in Acute Myocardial Infarction and the Effects on Short Term Mortality

Kyung Jin Kim; In Sook Kang; Kihwan Kwon; Wook Bum Pyun; Gil Ja Shin

doi:10.12771/emj.2013.36.1.26

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Kim, Kang, Kwon, Pyun, and Shin: The Differences of Left Ventricular Geometry in Acute Myocardial Infarction and the Effects on Short Term Mortality

Original Article

The Ewha Medical Journal

The Ewha Medical Journal 2013; 36(1): 26-34.

Published online: 25 March 2013

DOI: https://doi.org/10.12771/emj.2013.36.1.26

The Differences of Left Ventricular Geometry in Acute Myocardial Infarction and the Effects on Short Term Mortality

Kyung Jin Kim, In Sook Kang, Kihwan Kwon, Wook Bum Pyun, Gil Ja Shin

Division of Cardiology, Department of Internal Medicine, Ewha Womans University School of Medicine, Seoul, Korea.

Corresponding author: Gil Ja Shin, Division of Cardiology, Department of Internal Medicine, Ewha Womans University School of Medicine, 1071 Anyangcheon-ro, Yangcheon-gu, Seoul 158-710, Korea. Tel: 82-2-2650-2843, Fax: 82-2-2655-2076, giljshin@ewha.ac.kr

Received 14 February 2013 Accepted 13 March 2013

(open-access):

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objectives

This study designed to find the differences of left ventricular (LV) geometry in acute myocardial infarction (AMI) between ST elevation myocardial infarction (STEMI) and non ST elevation myocardial infarction (NSTEMI) and the occurrences of adverse outcome according to the LV geometry.

Methods

Comprehensive echocardiographic analyses were performed in 256 patients with AMI. The left ventricular mass index (LVMI) and relative wall thickness (RWT) were calculated. LV geometry were classified into 4 groups based on RWT and LVMI: normal geometry (normal LVMI and normal RWT), concentric remodeling (normal LVMI and increased RWT), eccentric hypertrophy (increased LVMI and normal RWT), and concentric hypertrophy (increased LVMI and increased RWT). Cox proportional hazards models were used to evaluate the relationships among LV geometry and clinical outcomes.

Results

Patients with NSTEMI were more likely to have diabetes mellitus, hypertension, heart failure, stroke and previous myocardial infarction. By the geometric type, patients with NSTEMI were more likely to have eccentric hypertrophy (n=51, 34.7% vs. n=24, 22.0%, P=0.028). There was no significantly different adverse outcome between STEMI and NSTEMI patients. Fifteen patients (5.9%, 7 female [46.7%]) died and the median duration of survival was 10 days (range, 1 to 386 days). Concentric hypertrophy carried the greatest risk of all cause mortality (hazard ratios, 5.83; 95% confidence interval, 1.04 to 32.7).

Conclusion

NSTEMI patients had more likely to have eccentric hypertrophy but adverse outcome after AMI was not different between STEMI and NSTEMI patients. Concentric hypertrophy had the greatest risk of short term mortality.

Keywords: Acute myocardial infarction, NSTEMI, Remodeling, STEMI, Survival

Introduction

Left ventricular (LV) dysfunction begins with some injury or stress on the myocardium and is generally a progressive process [1,2]. The principal manifestation of such progression is a change in the geometry and structure of the LV, that the chamber dilates, hypertrophies and becomes more spherical. This process referred to as cardiac remodeling [1]. Such architectural remodeling can be classified as eccentric or concentric [3]. Concentric hypertrophy is a result of systolic pressure overload whereas eccentric hypertrophy is a consequence of volume overload [3].

The concepts of LV geometry were applied largely in clinical studies of patients with hypertension [4]. The adaptation of the LV to hypertension leads to the development of different geometric patterns and the differences of geometry are used as a risk stratification tool [5]. Hypertensive patients with concentric hypertrophy have the highest incidence of cardiovascular events including death [6]. Subsequently LV geometry was applied to the patients after acute myocardial infarction (AMI). In a high risk AMI, concentric hypertrophy carries the greatest risk of adverse cardiovascular events including death [7] but uncertainty still persists with the independent prognostic value of LV geometric patterns especially after AMI. To further characterize the various geometric patterns of the left ventricle and to determine the influence of those patterns on prognosis in patients with AMI, and to evaluate the difference of LV geometry by the type of ST change, we analyzed the patients who were diagnosed AMI with their echocardiographic data.

Methods

1. Study population

The 298 patients admitted to coronary care unit in Ewha Womans University Mokdong Hospital for AMI between January 2009 and October 2011 were included. The patients who were suitable for clinical and echocardiographic data were 256 and they were constituted for the final study group. Median duration of follow-up was 212.5 days (mean, 212±174 days). Fifteen patients (5.9%, 7 female [46.7%]) died during the duration of follow-up and the median duration of survival was 10 days (range, 1 to 386 days).

2. Echocardiographic evaluation

Comprehensive echocardiography performed within 3.0 days (3.0±18.3 days) after admission. LV septal wall thickness, posterior wall thickness and cavity size were measured from the LV short-axis view by two-dimensionally guided M-mode echocardiography, with images of the left ventricle at the papillary muscle tip level [8]. The LV mass was calculated according to the following formula: LV mass (g)=0.80×{1.04×[(septal wall thickness in diastole + LV internal diastolic diameter + posterior wall thickness in diastole)³ - (LV internal diastolic diameter)³]} + 0.6 g [7,9,10]. The LV mass was indexed to body surface area and LV hypertrophy was considered present when echocardiographically derived LV mass index (LVMI) was>115 g/m² for men and >95 g/m² for women [7,9]. The relative wall thickness (RWT) was calculated as 2×(posterior wall thickness in diastole)/( LV internal diastolic diameter). Increased RWT was present when this ratio was >0.42 [7,9]. The sample was divided into 4 mutually exclusive groups on the basis of LV geometry: concentric hypertrophy (LV hypertrophy and increased RWT), eccentric hypertrophy (LV hypertrophy and normal RWT), concentric remodeling (normal LVMI and increased RWT), and normal geometry (normal LVMI and normal RWT) [7,9].

3. Statistical analysis

Continuous data are presented as mean±standard deviation. Baseline data were compared by means of the χ²-test for categorical variables and unpaired t test for continuous variables. Comparison between the subgroups with different patterns of LV geometry was done using ANOVA with Scheffe post hoc correction. Multivariable cox proportional hazards models were used to determine the independent prognostic value of LV geometric patterns. Statistical analyses were performed using SPSS ver. 18.0 (SPSS Inc., Chicago, IL, USA). A probability value P<0.05 was considered statistically significant.

Results

1. Clinical and echocardiographic characteristics stratified by LV geometry

LV geometry was classified into 4 groups. Eccentric hypertrophy was present in 75 patients (29.2%), concentric remodeling in 15 patients (5.9%), concentric hypertrophy in 14 patients (5.5%), and normal in 152 patients (59.4%). In total population, the mean age was 63.3±13.0 years and eighty patients were female (31.3%). Patients with eccentric hypertrophy and concentric hypertrophy were older than normal group and patients with eccentric hypertrophy were the oldest (P<0.001 to normal group). There was no significant difference of sex proportion between 4 groups. Medical history of diabetes mellitus (DM), hypertension, heart failure (HF), stroke and myocardial infarction (MI) were included. Prevalence of DM and hypertension were higher in patients with concentric hypertrophy with no statistical significance. Prevalence of HF was significantly different between 4 groups (P=0.001) and the patients with eccentric hypertrophy showed the highest. In addition, patients with LV hypertrophy had lower estimated glomerular filtration rate and lower hemoglobin level (Table 1). The mean LVMI was 107.7±31.3 g/m² (range, 49.9 to 253.3 g/m²) and the mean RWT was 0.34±0.08 (range, 0.13 to 0.66). The patients with LV hypertrophy had significantly lower ejection fraction, higher left atrial volume index (LAVI), higher E/e' and severe mitral regurgitation (Table 2).

2. Clinical and echocardiographic characteristics stratified by type of ST change

Type of ST change divided the patients into 2 groups. Patients with non ST elevation myocardial infarction (NSTEMI) were 147 (57.4%) and the patients with ST elevation myocardial infarction (STEMI) were 109 (42.6%). The patients with NSTEMI were older than the patients with STEMI (P<0.001). The patients with NSTEMI had higher female proportion than the patients with STEMI (P=0.004). In addition, the patients with NSTEMI had higher prevalence of DM (P=0.010), hypertension (P=0.001), HF P<0.001), stroke (P=0.004) and previous MI (P<0.001) significantly than the patients with STEMI. Whereas the patients with STEMI were younger (P<0.001), more likely to be men (P=0.004) and smokers (P=0.04) than the patients with NSTEMI. Additionally the patients with NSTEMI showed more eccentric hypertrophy significantly than the patients with STEMI (P=0.028), but the other LV geometric types were not significantly different. Besides patients with NSTEMI had lower estimated glomerular filtration rate and lower hemoglobin level (Table 3). Echocardiographic characteristics showed that the patients with NSTEMI had significantly higher LVMI and LAVI than the patients with STEMI (Table 4).

3. Relationship between LV geometry and clinical outcomes

Of the 256 patients, 15 patients (5.9%, 7 female [46.7%]) died, and 11 patients of them (4.3%) experienced a cardiovascular death. After discharged, 7 patients (2.7%) had coronary artery bypass graft, 6 patients (2.3%) were readmitted with HF, 4 patients (1.6%) had recurrent MI, and 5 patients (2.0%) had stroke. The incidence of cardiovascular event including recurrent MI, admission due to heart failure, cardiac death and stroke were not significantly different between LV geometric types and between STEMI and NSTEMI (Table 5).

In an univariate analysis for all-cause mortality, age, history of HF and eccentric hypertrophy carried higher risk (Fig. 1) but in a multivariate analysis, only concentric hypertrophy carried the greatest risk of all cause mortality (hazard rations [HR], 5.83; 95% confidence interval [CI], 1.04 to 32.72) (Fig. 2).

In an univariate analysis for cardiovascular mortality, age, history of HF and eccentric hypertrophy carried higher risk (Fig. 3) but in a multivariate analysis, age carried higher risk and history of DM carried lower risk but no specific LV geometry had significantly higher risk for cardiovascular mortality (Fig. 4).

Discussion

Remodeling may be physiological and adaptive during normal growth or pathological due to myocardial infarction and hypertension [11]. After myocardial infarction, myocyte necrosis and the resultant increase in load initiates dilatation, hypertrophy, and the formation of a discrete collagen scar. Ventricular remodeling may continue until the distending forces are counterbalanced by the tensile strength of the collagen scar. This balance is determined by the size, location, and transmurality of the infarct and the patency of the infarct-related artery [12]. Many studies have tried to find the implication of LV geometry in AMI, but the differences in LV geometry between STEMI and NSTEMI have not been studied. Therefore this study tried to evaluate the differences of LV geometry between STEMI and NSTEMI and found that the patients with NSTEMI had higher co-morbidities and higher rate of eccentric hypertrophy than the patients with STEMI significantly, but adverse outcome was not different between STEMI and NSTEMI patients.

Changes in LV geometry and structure strongly associated with major cardiovascular events [1,13-17]. However, discerning the independent prognostic value afforded by alterations in LV shape has proved more controversial [17]. There have been many studies tried to perceive the prognostic implications of LV geometry. Initially, the concepts of LV geometry were applied largely in clinical studies of patients with hypertension [4,18]. Koren et al. [6] were among the first to use M-mode echocardiography to study the relationship of LV geometry to clinical outcomes and the study showed that hypertensive patients with concentric hypertrophy revealed the highest incidence of cardiovascular events including death [6,7]. Subsequently, LV morphologic changes in patients after AMI and the relationship of such findings to clinical course were studied [19-23]. LV end-systolic and end-diastolic volumes are effective metrics for the severity of post-MI remodeling, and their changes are closely associated with clinical outcomes [24]. Within broader populations, LV mass is a cardiovascular risk factor independent of blood pressure [13,16,23,24]. Recently, Verma et al. [7] related echocardiographic patterns of LV remodeling an average of 5 days after MI to the incidence of subsequent cardiovascular events. Patients with concentric hypertrophy are at greatest risk for the combined end point of cardiovascular death, recurrent MI, HF, stroke, or resuscitation after cardiac arrest [7,24].

In this study, the subdivided groups stratified by LV geometry showed significantly different outcome. Eccentric hypertrophy showed significantly higher risk for all cause mortality (HR, 3.70; 95% CI, 1.21 to 11.30) and cardiovascular mortality (HR, 5.24; 95% CI, 1.35 to 20.25) on univariate analysis. But after adjustment with age, sex, history of DM, hypertension and HF, the significance of mortality risk disappeared and only concentric hypertrophy showed the highest risk of all cause mortality (HR, 5.83; 95% CI, 1.04 to 32.72). Postinfarction remodeling is divided into two phases. The early phase involves expansion of the infarct zone and late remodeling involves time-dependent dilatation, the distortion of ventricular shape, and mural hypertrophy [11]. Therefore, by 5 days, the expected structural change after MI would be characterized by early dilation and eccentric hypertrophy [24]. However, in this study, the LV geometry with the greatest risk of mortality after MI was concentric hypertrophy [7,25]. Konstam [24] suspected that this could be explained by understanding the role of antecedent hypertension and its structural consequences on the clinical course after MI. The pathologic hypertrophy, particularly concentric hypertrophy represents a marker for the systemic consequences of hypertension, including vascular remodeling and results in both cerebral and myocardial ischemic events [24]. In this study [24] and the study by Verma et al. [7], the relative prevalence of hypertension follows the same patterns as the relative incidence of subsequent clinical outcomes: concentric hypertrophy had the greatest risk of hypertension and eccentric hypertrophy, concentric remodeling and normal pattern were followed. Conclusively we can hypothesize that at the time of MI, antecedent structural consequences of hypertension carry the LV geometric change and also higher risk of mortality rate.

The limitation of this study is followings. First, 2-dimensional echocardiography is limited in its accuracy for measuring LV mass because all methods assume a uniform LV thickness. Second, this result is based on the patients with AMI which limits generalization. Third, the already known predictors of cardiovascular mortality, e.g., initial Killip class and severity of coronary vascular disease were not analyzed in this study. Finally, this study did not assess for serial changes in LV mass and its geometrical patterns and potential influence on cardiovascular risk. Therefore prospective study with serial echocardiographic analysis should be followed.

In this report, patients with NSTEMI were more likely to have eccentric hypertrophy but adverse outcome after AMI was not different between STEMI and NSTEMI patients. The baseline LV geometry represents the prognostic predictors to the patients with AMI and the concentric hypertrophy carries the greatest risk of short term mortality. Therefore routine assessment of LV mass and RWT can help us to assess the prognosis of the patients with AMI.

Figures and Tables

Fig. 1

Unadjusted hazard ratios (95% confidence intervals) for all cause mortality. Cox proportional hazards models are used. CI, confidence interval; DM, diabetes mellitus; HTN, hypertension; HF, heart failure; CR, concentric remodeling; EH, ecoentric hypertrophy; CH, concentric hypertrophy; Ref, referent value.

Fig. 2

Adjusted hazard ratios (95% confidence intervals) for all cause mortality. Multivariable Cox proportional hazards models are used. CI, confidence interval; DM, diabetes mellitus; HTN, hypertencsion; HF, heart failure; CR, concentric remodeling; EH, ecoentric hypertrophy; CH, concentric hypertrophy; Ref, referent value.

Fig. 3

Unadjusted hazard ratios (95% confidence intervals) for cardiovascular mortality. Cox proportional hazards models are used. CI, confidence interval; DM, diabetes mellitus; HTN, hypertension; HF, heart failure; CR, concentric remodeling; EH, ecoentric hypertrophy; CH, concentric hypertrophy; Ref, referent value.

Fig. 4

Adjusted hazard ratios (95% confidence intervals) for cardiovascular mortality. Multivariable Cox proportional hazards models are used. CI, confidence interval; DM, diabetes mellitus; HTN, hypertencsion; HF, heart failure; CR, concentric remodeling; EH, ecoentric hypertrophy; CH, concentric hypertrophy; Ref, referent value.

Table 1

Clinical characteristics stratified by left ventricular geometric patterns

Values are presented as mean±standard deviation or number (%). ^*P<0.01 versus patients with normal LV geometry. STEMI, ST elevation myocardial infarction; NSTEMI, non ST elevation myocardial infarction; PCI, percutaneous coronary intervention CABG, coronary artery bypass graft; eGFR, estimated glomerular filtration rate; CRP, C-reactive protein.

Table 2

Echocardiographic characteristics stratified by left ventricular geometric patterns

Values are presented as mean±standard deviation. EDVI, end-diastolic volume index; ESVI, end-systolic volume index; LVEF, left ventricular ejection fraction; RWT, relative wall thickness; LVMI, left ventricular mass index; LAVI, left atrial volume index; DT, deceleration time; MR, mitral regurgitation. ^*P<0.01 vs. patients with normal left ventricular geometry.

Table 3

Clinical characteristics stratified by type of ST change

Values are presented as mean±standard deviation or number (%). NSTEMI, non ST elevation myocardial infarction; STEMI, ST elevation myocardial infarction; PCI, percutaneous coronary intervention; CABG, coronary artery bypass graft; eGFR, estimated glomerular filtration rate.

Table 4

Echocardiographic characteristics stratified by type of ST change

Values are presented as mean±standard deviation. NSTEMI, non ST elevation myocardial infarction; STEMI, ST elevation myocardial infarction; EDVI, end-diastolic volume index; ESVI, end-systolic volume index; LVEF, left ventricular ejection fraction; RWT, relative wall thickness; LVMI, left ventricular mass index; LAVI, left atrial volume index; DT, deceleration time; MR, mitral regurgitation.

Table 5

Clinical outcomes stratified by left ventricular geometric patterns and by type of ST change

Values are presented as number (%). NSTEMI, non ST elevation myocardial infarction; STEMI, ST elevation myocardial infarction; CABG, coronary artery bypass graft.

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