chocardiography and 6-minute walk test in left ventricular systolic dysfunction

Abstracts

FUNDAMENTO: Insuficiência cardíaca crônica é um grave distúrbio cardiovascular. OBJETIVO: O objetivo deste estudo foi avaliar prospectivamente se o resultado do teste de caminhada de 6 minutos (TC-6M) se correlaciona com as variáveis ecocardiográficas em pacientes portadores de disfunção sistólica do ventrículo esquerdo e insuficiência cardíaca crônica estável. MÉTODOS: Foram estudados prospectivamente 52 pacientes (65% homens; média de idade de 60±11 anos) portadores de insuficiência cardíaca crônica secundária à cardiopatia isquêmica ou miocardiopatia idiopática. Todos os pacientes apresentavam disfunção sistólica do ventrículo esquerdo (fração de ejeção <0.45) e encontravam-se em insuficiência cardíaca classe funcional II ou III da NYHA. Foram realizados um estudo de eco-Doppler e um TC-6M no mesmo dia. RESULTADOS: O TC-6M apresentou correlação moderada, mas estatisticamente significante, com o diâmetro sistólico final - DSF (r=-0,46; p=0,0006), com a fração de encurtamento - FEn (r=0,52; p=0,0001) e com a fração de ejeção (FE) (r=0,5; p=0,0001), e apresentou correlação fraca, mas estatisticamente significante, com o índice de desempenho miocárdico - IDM (r=-0,39; p=0,0046), a relação E/A (tricúspide) (r=-0,333; p=0,016), o tempo de aceleração do fluxo pulmonar (r=0,328; p=0,018), e com a amplitude do eixo longo lateral (r=0,283; p=0,04). O modelo de regressão linear demonstrou que a idade (χ2=-0,59, p=<0,001), o padrão de enchimento restritivo transmitral (χ2=-0,44, p=0,004) e a dimensão sistólica final do ventrículo esquerdo (χ2=-0,34, p=0,012) foram fatores independentes que influenciam o TC-6M. CONCLUSÃO: Em pacientes portadores de insuficiência cardíaca decorrente de disfunção sistólica do ventrículo esquerdo, o TC-6M como ferramenta de avaliação clínica da capacidade funcional apresenta uma correlação significante com os principais parâmetros da função sistólica global do VE e com o IDM do VE. Em pacientes com disfunção sistólica do VE, a idade, o padrão de enchimento restritivo transmitral e a dimensão sistólica do ventrículo esquerdo mostraram-se independentemente associados ao TC-6M.

Insuficiência cardíaca; ecocardiografia; caminhada; qualidade de vida

FUNDAMENTO: La insuficiencia cardiaca crónica es un grave disturbio cardiovascular. OBJETIVO: El objetivo de este estudio fue evaluar prospectivamente si el resultado de la prueba de caminata de 6 minutos (PC-6M) se correlaciona con las variables ecocardiográficas en pacientes portadores de disfunción sistólica del ventrículo izquierdo e insuficiencia cardiaca crónica estable. MÉTODOS: Se estudiaron prospectivamente a 52 pacientes (el 65% varones; promedio de edad de 60±11 años) portadores de insuficiencia cardiaca crónica secundaria a la cardiopatía isquémica o la miocardiopatía idiopática. Todos los pacientes presentaban disfunción sistólica del ventrículo izquierdo (fracción de eyección <0.45) y se encontraban en insuficiencia cardiaca clase funcional II ó III de la NYHA. Se realizaron un estudio de Ecocardiografía Doppler y una PC-6M en el mismo día. RESULTADOS: La PC-6M presentó correlación moderada, pero estadísticamente significante, con el diámetro sistólico final (DSF): r=-0,46; p=0,0006; con la fracción de acortamiento (FA): r=0,52; p=0,0001; y con la fracción de eyección (FE): r=0,5; p=0,0001. Presentó también correlación débil, pero estadísticamente significante, con el índice de desempeño miocárdico (IDM): r=-0,39; p=0,0046; la relación E/A (tricúspide): r=-0,333; p=0,016; el tiempo de aceleración del flujo pulmonar: r=0,328; p=0,018; y con la amplitud del eje largo lateral: r=0,283; p=0,04. El modelo de regresión lineal evidenció que la edad (χ2=-0,59, p=<0,001), el patrón de llenado restrictivo transmitral (χ2=-0,44, p=0,004) y la dimensión sistólica final del ventrículo izquierdo (χ2=-0,34, p=0,012) fueron factores independientes que influencian la PC-6M. CONCLUSIONES: En pacientes portadores de insuficiencia cardiaca resultante de disfunción sistólica del ventrículo izquierdo, la PC-6M como herramienta de evaluación clínica de la capacidad funcional presenta una correlación significante con los principales parámetros de la función sistólica global del VI y con el IDM del VI. En pacientes con disfunción sistólica del VI, la edad, el patrón de llenado restrictivo transmitral y la dimensión sistólica del ventrículo izquierdo se mostraron independientemente asociados a la PC-6M.

Insuficiencia cardiaca; ecocardiografía; caminata; calidad de vida

ORIGINAL ARTICLE

Echocardiography and 6-minute walk test in left ventricular systolic dysfunction

Venera Berisha^I; Gani Bajraktari^I; Dritero Dobra^II; Edmond Haliti^I; Reshat Bajrami^I; Shpend Elezi^II

^ISecond Division of Cardiology, Internal Medicine Clinic, University Clinical Center of Kosova, Prishtina - Kosovo

^IIMedical School, University of Prishtina, Prishtina - Kosovo

Mailing address

SUMMARY

BACKGROUND: Chronic heart failure is a major cardiovascular disorder.

OBJECTIVE: The aim of this study was to prospectively examine whether a 6-min walk test (6-MWT) result correlates with echocardiographic variables in patients with left ventricular systolic dysfunction and stable chronic heart failure.

METHODS: We prospectively studied 52 patients (65% male; mean age 60±11 years) who had chronic heart failure secondary to ischemic heart disease or idiopathic cardiomyopathy. All patients had left ventricular systolic dysfunction (ejection fraction <0.45), and were in stable NYHA class II or III heart failure. An echo-Doppler study and a 6-MWT were performed on the same day.

RESULTS: 6-MWT had moderate, but statistically significant correlation with end-systolic diameter (ESD) (r=-0.46; p=0.0006), with shortening fraction-SF (r=0.52; p=0.0001), and with ejection fraction-EF (r=0.5; p=0.0001), whereas it had poor, but statistically significant correlation with myocardial performance index-MPI (r=-0.39; p=0.0046), E/A(tricuspid) ratio (r=-0.333; p=0.016), pulmonary acceleration time (r=0.328; p=0.018), and lateral long axis amplitude (r=0.283; p=0.04). Linear regression model demonstrated that age (χ²=-0.59, p=<0.001), restrictive transmitral filling pattern (χ²=-0.44, p=0.004) and left ventricular end-systolic dimension (χ²=-0.34, p=0.012) were independent factors that influenced the 6-MWT.

CONCLUSION: In patients with heart failure due to left ventricular systolic dysfunction, the 6-MWT as a clinical assessment tool of the functional capacity has a significant correlation with the most important global LV systolic function parameters, as well as with LV MPI. In patients with LV systolic dysfunction, age, restrictive transmitral filling pattern, and left ventricular systolic dimension, were independently associated with the 6-MWT.

Key words: Heart failure; echocardiography; walking, quality of life.

Introduction

Chronic heart failure is a major cardiovascular disorder with increasing incidence and prevalence¹. Two-dimensional and Doppler echocardiography is a sensitive and noninvasive method of detecting cardiac abnormalities and systolic and/or diastolic dysfunction². Variables of diastolic filling allow further identification of subgroups with divergent long-term prognoses³. Recently, myocardial performance index (MPI) has been suggested for the evaluation of ventricular function⁴. MPI is calculated from the pulsed Doppler recordings of ventricular inflow and outflow velocities, and thus combines both systolic and diastolic ventricular performance. It reflects global ventricular function and is less affected by localized segmental wall motion abnormalities, in addition to playing an important prognostic role in the diagnosis of heart failure⁵ and in the prediction of cardiac events in patients with acute myocardial infarction⁶. The severity of congestive heart failure is usually graded according to patients' symptoms, in particular to the physical activity that induces dyspnea or fatigue. The NYHA functional heart failure classification meets only some of these criteria. However, the NYHA classification is based on the patient's self-assessment and its reliability is still a matter of debate⁷. The ideal instrument for risk stratification and optimal clinical management of congestive heart failure patients should be objective, as well as simple, inexpensive and safe. The peak oxygen uptake, measured during cardiopulmonary exercise testing is a more objective parameter to assess functional capacity and to predict survival in patients with heart failure^8-10. However, this method is limited only to specialized centers, because it requires sophisticated equipment and specially trained personnel.

The 6-min walk test (6-MWT) has been proposed as a simple and accurate alternative technique for measurement of submaximal exercise capacity in congestive heart failure patients¹¹. It is considered to be realistically related to daily physical activity. Consequently, it has been incorporated into studies of assessment of exercise capacity^12,13, of quality of life¹⁴, of efficacy of new therapeutic agents^15-17, including beta-blockers^18-22, of physical training programs²³ and of prognostic stratification^24-29.

The aim of the present study was to asses the relationship between 2-dimensional and Doppler echocardiographic parameters and 6-MWT in patients with heart failure and left ventricular systolic dysfunction. 6-MWT is used as a proxy measure of the quality of life; therefore, echocardiographic parameters that have independent association with 6-MWT would facilitate prediction of the quality of life.

Methods

Study population

The study group included 52 patients with stable chronic heart failure secondary to ischemic heart disease or idiopathic cardiomyopathy, referred to the Second Division of Cardiology at the Internal Medicine Clinic of the University Clinical Center of Kosova, in Prishtina, Kosovo, between December 2005 and April 2007.

The mean age was 60±11 years. The cause of heart failure was idiopathic dilated cardiomyopathy in 19 patients and ischemic cardiomyopathy in 33 patients. All patients had an enlarged left ventricle (left ventricular [LV] diastolic dimension >5.7cm) and global left ventricular systolic dysfunction (left ventricular ejection fraction [LVEF] <0.45), and all were in stable New York Heart Association (NYHA) functional class II or III heart failure. The functional capacity of 27 patients was class II and that of the remaining 25 was class III. Table 1 summarizes the patients' clinical and laboratory characteristics.

Patients with rhythm disturbances (atrial fibrillation, serious ventricular arrhythmias), patients who had decompensated heart failure, limitation of physical activity due to factors other than exertional dyspnea and fatigue (such as arthritis), and those with moderate to severe renal failure, with chronic obstructive pulmonary disease were excluded from the study. We also excluded patients who had experienced unstable angina, acute myocardial infarction or stroke, anemia, and any febrile condition or infectious disease.

The study was approved by the Institutional Ethics Committee and all patients gave their written informed consent. Standard medical therapy with e.g. ACE-inhibitors, beta-blockers, digoxin and diuretics was individually optimized based on symptoms and renal function at least 2 weeks prior to exercise testing. All patients continued to take their routine medication when the echocardiography and 6-MWT were performed.

Data collection

The history and physical examination was performed in all subjects. In all patients the routine biochemical measurements were performed: the measurements of erythrocytes, leucocytes, hemoglobin, hematocrit, erythrocyte sedimentation, BUN, creatinine, blood glucose, cholesterol, triglycerides and inflammatory blood analysis (fibrinogen, CRP). Measurements of weight, height, waist and hip were also performed.

Echocardiographic examinations

Echocardiographic examination was performed using a Philips Intelligent E-33 echocardiograph with a multi-frequency transducer, and harmonic imaging as appropriate. All echocardiographic studies were performed by the same investigator. The echocardiographic study was performed in the left lateral decubitus in the parasternal long-axis and 4-chamber views.

The cross-sectional, two-dimensionally guided M mode recordings of LV short axis were performed using the left parasternal long axis view with the cursor at the tips of the mitral valve leaflets. Fractional shortening was calculated as the percentage fall in LV cavity dimension during systole in relation to that at end-diastole. Left ventricular ejection fraction was estimated using Simpson's biplane method. Left atrial dimension was measured from M-mode recordings with the cursor crossing the aortic root at the level of the aortic valve leaflets. LV long axis M-mode recordings were obtained with the cursor positioned at the lateral and septal angles of the mitral ring and right ventricular long axis recording with the cursor positioned at the lateral angle of the tricuspid ring. All M-mode recordings were zoomed to obtain better images for accurate measurements.

Diastolic function of the left and right ventricles was assessed by pulsed Doppler. The pulsed Doppler sample volume was positioned at the tips of the mitral and tricuspid leaflets, respectively. We registered the E wave, A wave, from which the E/A ratio was calculated, and the deceleration time of E wave (DT-E). We also registered Er wave, Ar wave and Er/Ar ratio.

The MPI was measured from mitral inflow and LV outflow velocity-time intervals as described by Tei et al³⁰. The a interval measured from the cessation to the onset of mitral inflow is equal to the sum of isovolumetric contraction time (ICT), ejection time (ET), and isovolumetric relaxation time (IRT). Left ventricular ejection time b is the duration of left ventricular outflow velocity profile. Thus the sum of ICT and IRT was obtained by subtracting b from a. The index of combined LV systolic and diastolic function (the sum of ICT and IRT divided by ejection time) was calculated as (a - b) / b (Fig.1). The IRT can be measured by subtracting the d interval, between the R wave and the cessation of LV outflow, from the c interval, between the R wave and the onset of mitral inflow. ICT was calculated by subtracting the IRT from a-b.

Mitral regurgitation severity was assessed by color and continuous wave Doppler and was graded as mild, moderate, or severe according to the jet distance from the valve orifice and flow velocity profile, respectively, in line with the recommendations of the American Society of Echocardiography³¹. Likewise, tricuspid regurgitation was assessed by color flow and continuous-wave Doppler from the apical four-chamber view. Retrograde transtricuspid pressure drop > 35 mmHg was taken as a sign of pulmonary hypertension when the right atrium was not dilated.

6-min walk test

Within 24 h of echocardiographic examination, a 6-MWT was performed on a level hallway surface; the test was administered by a registered nurse blinded to the results of echocardiography. According to the method of Gyatt et al^11,12 all patients were informed of the purpose, methods and use of the 6-min walk test results. The 6-MWT was conducted following a standardized protocol, between 10 am and 4 pm after usual medication¹¹. A 15 m flat, obstacle-free corridor, with chairs placed at either end was used. Patients were instructed to walk as far as possible, turning 180º every 15 m in the allotted time of 6 minutes. Patients walked unaccompanied so as not to influence walking speed, and they were asked to walk as far as possible within 6-minutes. Patients were permitted to rest, if needed, then they were told of the remaining time at every two minutes. At the end of the 6 min, the physician measured the total distance walked by the patient.

Statistical analysis

Data are presented as mean ± SD or proportions (% of patients). Continuous data are compared with two-tailed unpaired Student's t test. Discrete data are compared with chi- square test. Correlation between variables was performed using Pearson's correlation test. A p value < 0.05 was considered to indicate statistical significance. Multivariate analysis was performed using linear regression model. Factors included in this model were age, restrictive transmitral filling pattern, left ventricular systolic dimension, myocardial performance index and diabetes mellitus.

Results

The clinical and laboratory characteristics of the 52 patients enrolled in the study are shown in Table 1, and the echocardiographic and Doppler measurements are shown in Table 2. There was a moderate, but statistically significant correlation of 6-MWT with LV posterior wall thickness ( r= 0.49; p<0.001), left ventricular end-systolic dimension (r=-0.46, p<0.001, Fig.2), LV fractional shortening (r = 0.517, p<0.001, Fig. 3), and LVEF (r = 0.50, p<0.001), whereas there was a poor, but statistically significant correlation with myocardial performance index-MPI (r=-0.39; p=0.0046, Fig. 4), E/A (tricuspid) ratio (r=-0.333; p=0.016), pulmonary acceleration time (r=0.328; p=0.018), and lateral long axis amplitude (r=0.283; p=0.04) (Table 3). The dimensions of aorta, left atrium, interventricular septal thickness, E wave, A wave, E/A ratio, deceleration time of E wave, E (tricuspid) wave, A (tricuspid) wave, E (tricuspid) /A (tricuspid) ratio, deceleration time of E (tricuspid) and LV septal long axis amplitude had no significant correlation with 6-MWT (Table 3).

Multivariate analysis was performed using linear regression model. Results of this model (Table 4) demonstrated that age, restrictive transmitral filling pattern and left ventricular end-systolic dimension were independent factors that influence the 6-MWT. All these parameters were inversely related to the 6-MWT. Age of the patients emerged as the strongest independent predictive factor, followed by restrictive filling pattern and left ventricular end- systolic dimension.

Discussion

To our knowledge, this is the first study to correlate 6-MWT performance in patients with chronic heart failure. The main finding of our study is that the 6-MWT has a moderate, but statistically significant correlation with LV systolic dimension, global LV systolic function parameters, LV MPI, as well as with long axis systolic function of left and right ventricles in patients with chronic stable heart failure due to LV systolic dysfunction.

Another finding of our study was that age, restrictive transmitral filling pattern, and left ventricular systolic dimension are independently related to the 6-MWT in stable chronic heart failure patients due to left ventricular systolic dysfunction, without rheumatic valvular heart disease.

Heart failure is an epidemiological entity that is increasing worldwide, and now represents a major health problem in most developed countries¹. The measurement of quality of life in heart failure patients has proved more elusive than what was anticipated. It is still unclear which one is better for the assessment of grading of heart failure: if the judgment of the physician, the use of the NYHA classification or the use of many sophisticated questionnaires.

The 6-MWT was originally used by physicians to assess patients with lung disease^32,33, and later was introduced as an alternative objective measure of submaximal exercise capacity of congestive heart failure patients¹¹. Previous studies show controversial results about the correlation of 6-MWT with functional exercise capacity in chronic heart failure patients. The 6-min walk test was shown to be correlated with peak oxygen uptake in dilated cardiomyopathy and to have a predictive value in these patients^34-36. The 6-MWT was also shown to be a useful prognostic marker in these patients^26,27,37. However, Opasich et al³⁸ demonstrated that in moderate to severe chronic heart failure patients, the 6-min walk test is not related to cardiac function and only moderately related to exercise capacity.

It was also proven that the 6-MWT distance was improved after a follow-up in patients with LV systolic dysfunction that received ACE-inhibitors^39,40, new-generation beta-blockers^18-22, and underwent exercise training²³.

There are several clinical implications that could be suggested from this study. Several important echocardiographic parameters are independently related to 6-MWT and therefore can be used to predict the quality of life of the patients. Age emerged as an independent factor inversely related to 6-MWT. Therefore, independently from echocardiographic results, the quality of life deteriorates with age probably due to complex factors associated with aging.

The small number of patients could be mentioned as a limitation of this study, especially for the comprehensive multivariate analysis.

In conclusion, in patients with heart failure due to left ventricular systolic dysfunction, the 6-MWT as a clinical assessment tool of the functional capacity has a significant correlation with the most important global LV systolic function parameters, as well as with LV MPI. In patients with LV systolic dysfunction, age, restrictive transmitral filling pattern, and left ventricular systolic dimension, were independently associated with the 6-MWT.

Potential Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Sources of Funding

There were no external funding sources for this study.

Study Association

This study is not associated with any post-graduation program.

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Publication Dates

• Publication in this collection
  06 Apr 2009
• Date of issue
  Feb 2009

History

• Received
  21 Jan 2008
• Reviewed
  18 Feb 2008
• Accepted
  29 Feb 2008