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European Journal of Heart Failure 2000 2(3):273-280; doi:10.1016/S1388-9842(00)00091-X
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© 2000 European Society of Cardiology

Comparison of different methods of functional evaluation in patients with chronic heart failure

Carlo Rostagno*, Giorgio Galanti, Marco Comeglio, Vieri Boddi, Giuseppe Olivo and Gian Gastone Neri Serneri

Istituto di Clinica Medica e Cardiologia, Università di Firenze Viale GB Morgagni 85, 50134 Florence, Italy

* Corresponding author. Tel.: +39-055-436-0976; fax: +39-055-427-7608. E-mail address: g.gensini{at}dfc.unifi.it (C. Rostagno).


   Abstract
Top
 Abstract
1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 References
 
Background: Stratification of the severity of heart failure has major prognostic and therapeutic implications.

Aims: To prospectively compare different methods of assessment of functional capacity in patients with chronic heart failure (CHF).

Methods and results: We studied 143 patients (78 male and 65 female) with CHF aged less than 70 years (mean 57.3 years). Functional assessment was made clinically according to NYHA classification and according to the Goldman Activity Scale Classification (GASC). Cardiovascular performance was measured by peak O2 consumption (pVO2) and anaerobic threshold (AT) at cardiopulmonary exercise test and by the distance walked during a 6-min walk test (6-MWT). Clinical scales resulted significantly related. Peak VO2 and AT showed a mild relation with distance covered at 6-MWT (r = 0.56 and r = 0.46, respectively). Concordance between NYHA classification and levels of performance at cardiopulmonary exercise test or at 6-MWT was less than 50%.

Conclusion: Our results suggest that none of the usually employed methods give a definitive assessment of functional capacity of cardiovascular system and a high degree of discordance exists among the results of different tests in the same patient. Although NYHA classification maintains its value in clinical evaluation of patients with CHF, the 6-min walk test is recommended in patients with mild-to-moderate CHF (II–III NYHA classes) as a simple and useful screening test to select patients for further diagnostic evaluation.

Key Words: Chronic heart failure • Goldman Activity Scale Classification (GASC) • Cardiovascular performance

Received December 22, 1999; Revised April 10, 2000; Accepted May 23, 2000


   1. Introduction
Top
 Abstract
 1. Introduction
2. Material and methods
 3. Results
 4. Discussion
 References
 
Some of the greatest problems in chronic heart failure (CHF) are to categorize the degree of the impairment of cardiac performance and of cardiovascular disability in order to follow the clinical status of patients over time, to assess the effects of therapeutic interventions and to compare patients with each other [1]. A number of methods has been suggested to categorize CHF patients including methods based on the history, such as NYHA classification and Goldman Specific Activity Scale (GSAS) [2,3], or methods which can directly evaluate cardiovascular function such as the measurement of maximal oxygen consumption during an exercise stress test or the distance walked in 6 min [4,5]. NYHA classification is the more widespread method used to stratify CHF, however, like GSAS, is limited by a low reproducibility and by a large degree of subjectivity and is not sensitive enough to reflect small but sometimes important clinical changes [6,7]. The measurement of maximal or peak oxygen consumption during cardiopulmonary tests offers an objective evaluation of cardiovascular function, which is provided with high prognostic value in severe heart failure [8–11]. A peak O2 (pVO2) consumption <10 ml/kg per min is a fully accepted indication for the need for a heart transplant, while a pVO2<14 ml/kg per min combined with a major functional limitation is a probable indication for the need for a heart transplant [8,11–13]. Nevertheless, the cardiovascular exercise test is time consuming, requires relatively expensive instruments, an experienced team and several patients, in particular, the oldest are not able to perform a maximal cardiopulmonary test or wear the mask for the analysis of oxygen consumption. The 6-min walk test has been proposed as an easy, non-expensive alternative method to evaluate cardiopulmonary functional capacity [14]. The test showed reproducible results in patients with CHF [15] and has been demonstrated to be of prognostic value in different subsets of patients [16–18].

Despite the large number of investigations on the evaluation of cardiovascular function [8,10,19,20] only a few studies have been directly and prospectively addressed to compare the different methods used to stratify CHF patients and in particular limited information exists about the relation between pVO2 and 6-min walk test [21,22]. Moreover, most of the previous studies were performed in selected groups of patients with CHF, which included few, if any, women. Therefore, we planned the present study to prospectively compare clinical methods (NYHA classification, GSAS) with functional methods (cardiopulmonary exercise test and the 6-min walk corridor test) in an unselected group of patients of both gender who could better reflect the population observed in clinical practice.


   2. Material and methods
Top
 Abstract
 1. Introduction
 2. Material and methods
3. Results
 4. Discussion
 References
 
2.1. Characteristics of the patients
We studied 143 patients with symptomatic CHF (<70 years) who were consecutively admitted to our institution from 1 January 1995 to 30 June 1996. Of the patients, 78 were male and 65 female whose age ranged from 29 to 70 (mean age 57.3 years). Aetiology of heart failure is shown in Table 1. Patients with recent myocardial infarction (<3 months) or primary lung disease were excluded from the study. As control we studied 28 healthy subjects (mean age 59.7 years). Eighty two percent of patients were in treatment with ACE-inhibitors and 71% with digoxin at the moment of the study, while dosage of diuretics (57% were treated with furosemide) had not been changed in the 48 h preceding the functional evaluation.


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  		Table 1
 
2.1.1. Study design
On hospital admission patients underwent a careful physical examination and a detailed cardiovascular history was collected. Physicians (C.R. and G.G.N.S.) assessed the clinical status according to NYHA and Goldman classifications. Within 2 days of hospital stay all the patients underwent chest X-ray, echocardiographic evaluation and peak expiratory flow measurement. Cardiopulmonary stress testing and 6-min walk corridor tests were performed in 2 subsequent days at the same hour in the morning in a randomly assigned sequence. The ethical committee of our hospital approved the study.

2.2. Clinical methods of evaluation of functional capacity
During baseline evaluation the severity of symptoms was assessed using the New York Heart Association functional classification [2]. Moreover, patients were stratified according to the Specific Activity Scale proposed by Goldman et al. [3]. To reduce the degree of subjectivity of the NYHA classification these authors ideated a questionnaire in which the patient was asked for its ability to perform a variety of personal care, housework, occupational and recreational activities each with a different determined metabolic cost. A patient was assigned to a Specific Activity Scale functional class according to the metabolic consumption associated with the most intense activity that the patient could perform.

2.3. Cardiopulmonary exercise test
The cardiopulmonary exercise test was performed using an incremental treadmill stress testing according to the modified Bruce’s protocol [23]. During the test, arterial pressure and 12-leads electrocardiogram were monitored. Cardiopulmonary functional capacity was assessed by determining the anaerobic threshold and the peak of oxygen consumption by expired gas analysis (OXYCON ALFA-JAEGER, Wuerzburg, Germany). Anaerobic threshold was determined according to Wasserman et al. [24]. In relation to their cardiovascular capacity, patients were subdivided into four groups according to Weber’s classification [25]: class A included patients with a pVO2>20 ml/kg per min; class B were patients with a pVO2 between 16 and 20 ml/kg per min; class C between 10 and 16 ml/kg per min; and class D between 6 and 10 ml/kg per min.

2.4. The 6-min walk test
The 6-min walk test was performed in an indoor corridor, 25 m long, according to the suggestions of Guyatt et al. [14]. Patients were asked to walk the corridor at the higher rate from one end to the other, as many times as possible, in the established time. The test was performed under the control of a physician who encouraged the patients with phrases like: ‘you are doing well’ or ‘you are doing a good job’. At the end of the 6-min the physician measured the distance walked by the patient. On the basis of subdivision in quartiles of the distance walked, performance was grouped into four different levels (level I>420 m, level II 340–420 m, level III 260–340 m, level IV <260 m). The repeatability of the test was assessed in 50 patients by performing the test twice in the same day.

2.5. Other measurements
Echocardiographic examination was performed in the left side recumbent position using a SIM 5000 echocardiograph (Esaote Biomedica, Florence, Italy) with monoplane probes (2.50 and 3.75 MHz). Measurements were calculated according to the recommendations of the American Society of Echocardiography [26]. Mean pulmonary artery pressure was calculated by the acceleration time method [27], while the cardiac output was measured by the formula CSAxVTIxHR, where CSA is the aortic cross sectional area, VTI is the systolic velocity integral and HR is the heart rate [28].

The peak expiratory flow rate (PEFR) was measured by a flow-meter (Mini-Wright flow meter, Armstrong Industries Inc, Northbrook, IL, USA). The test was performed at the patient’s bed, in the sitting position. The highest of three attempts was recorded. The cardiothoracic index was measured on a standard chest X-ray performed in the postero-anterior projection.

2.6. Statistical analysis
Results were expressed as the mean±S.D. Differences among groups were evaluated using the Student’s t-test. Correlation among pVO2, AT and distance at 6-min walk test and other variables were evaluated using the standard regression coefficient analysis. For correlation between NYHA classification and continuos variables we used the Spearman rank correlation coefficient, which allows a valid measure of strength of association if the underlying variable is originally ranked and not measured. Baseline measurements of pVO2, AT and distance at 6-min walk test as the assessment of functional capacity according to NYHA and Goldman classification were stratified into four categorized variables. The Jonckheree–Tepstra was used to test the null hypothesis of equality of k populations against ordered alternatives. A value of P<0.05 was considered statistically significant.


   3. Results
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
4. Discussion
 References
 
The clinical characteristics of patients with heart failure, stratified according to NYHA classification, and of the control group are shown in Table 2. Table 3 represents the results of the cardiopulmonary test and the 6-min walk corridor test in relation to the NYHA class.


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  		Table 2 Characteristics of patients in relation to NYHA functional classa

 


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  		Table 3 Results of functional evaluation according to NYHA functional class

 
3.1. Relations among indexes of cardiac function and different methods of functional classification
At Spearman rank-correlation test functional capacity expressed according to NYHA classification was significantly related to commonly used indices of left ventricular function such as ejection fraction (r=–0.53, P<0.0000), left ventricular circumferential shortening (r=–0.63, P<0.0000) and left ventricular end diastolic diameter (r=0.58, P=0.000). Moreover, NYHA classification was significantly related to calculated mean pulmonary artery pressure (r=0.60, P<0.0000). We were not able to find any significant relation among pVO2, AT or distance walked during the 6-min walk test and any of the indexes of left ventricular function. Peak VO2 and anaerobic threshold (AT) were significantly related to calculated mean pulmonary artery pressure (r=0.59 and r=0.53, respectively), while pVO2 and the distance covered at walk test, and to a lesser extent AT, were related to peak expiratory flow rate (PEFR) (Table 4). Similar results were found at multivariate analysis (Table 5).


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  		Table 4 Relation among different methods of functional evaluation and cardiocirculatory parameters

 


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  		Table 5 Relation among different methods of functional evaluation and cardiocirculatory parameters at multivariate stepwise analysis

 
3.2. Relation among different methods
The two clinical classifications showed a good relation (NYHA, GSAS) while the relation between clinical classification and the results of objective functional evaluation (cardiopulmonary exercise test, 6-min walk corridor test) was remarkably weaker. A mild degree of relation was found between the different objective methods of functional evaluation themselves (AT and peak VO2 vs. 6-min walk corridor test) (r=0.46 and r=0.56, respectively).

The concordance between stratification according to NYHA criteria and the four level of performance for the 6-min walk test is shown in Table 6. The categorization according to NYHA classification correctly identified the level of functional capacity assessed by the 6-min walk corridor test in 47/141 patients (33%) (stand JT(x)=5.79 P<0.000). A normal performance (distance walked>420 m) was found in 66% of age-matched controls. In patients with higher functional capacity (distance covered at walk test>420 m=level I) the two methods agreed in 50% of the patients (13/26). The concordance was higher in patients with more severe CHF; in fact, eight out of nine patients in NYHA class IV covered <260 m during the walk test (level IV performance). Nevertheless, a level IV performance was found in 16 out of 39 patients in class III (41%) and in 11 out of 57 in class II (19%).


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  		Table 6 Relation between NYHA functional evaluation and level of performance at 6-min walk corridor testa

 
A concordance between peak VO2 categorized according to Weber classification and NYHA classification was found in 28/67 patients (41.7%) (stand JT(x)=2.79, P=0.0054). Fifty-two percent of patients classified in NYHA class I had a peak VO2>20 ml/kg per min (Weber class A), however, also 16/27 patients (60%) classified in NYHA class II and III had a pVO2>20 ml/kg per min (Table 7).


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  		Table 7 Relation between NYHA functional classification and measured pVO2 according to Weber classificationa

 
The comparison between NYHA classification and anaerobic threshold is shown in Table 8. Overall concordance between the two methods was low (35%) (stand JT(x)=2.35, P=0.0167). Although 19 patients were classified in NYHA classes III or IV, only one out of 64 patients was classified in Weber class C (AT between 8 and 11 ml/kg per min). Sixteen out of 20 patients in NYHA class I were in Weber class A (AT>14 ml/kg per min) but also 62% of patients in NYHA class II to IV had AT>14 ml/kg per min.


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  		Table 8 Relation between NYHA functional classification and measured AT according to Weber classificationa

 
A concordance between the level of performance at walk corridor test and peak VO2 consumption was found in 42% of patients (stand JT(x)=3.63, P=0.0001) (Table 9). Six out of 16 patients performing more than 420 m during the 6-min walk test were in Weber class B. On the contrary, 57% of patients in Weber class A performed less than 420 m during the 6-min walk test. A large overlap was found between patients in the other classes.


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  		Table 9 Relation between level of performance at 6-min walk corridor test and measured pVO2 according to Weber classa

 
Similar results were found when the performance for the 6-min walk tests were compared to AT (stand JT(x)=2.46, P=0.0143) (Table 10). Twelve out of 14 patients (85%) who walked more than 420 m during the 6-min walk test were in Weber class A, while only 38% of patients in class A performed more than 420 m during the 6-min walk test.


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  		Table 10 Relation between level of performance at 6-min walk corridor test and measured AT according to Weber classa

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
References
 
The results from the present investigation indicate that in patients with chronic heart failure exists a poor relation between clinical methods of functional evaluation such as NYHA classification or GSAS and the results of cardiovascular functional test (cardiopulmonary exercise test and 6-min walk test) or between functional test themselves. Moreover, as previously reported [29–31], we found a mild relation among indices of left ventricular systolic or diastolic function at rest and exercise capacity assessed both directly and clinically.

The methods to evaluate functional capacity in patients with CHF have been extensively investigated, however, few studies have been directly and prospectively addressed to compare the concordance among the methods usually employed [21,22]. Moreover, most of the previous investigations included selected populations with a large prevalence of males [15–22], at variance with our investigation in which women were 45% of the group under study.

As expected, we found a good concordance between the two clinical classifications under investigation. Our findings suggest that the Goldman Specificy Activity Scale does not offer significant advantages over the NYHA classification, which is easier to use. This is in contrast with the study of Varani et al. [32], which supports the superiority of the Goldman Scale in the evaluation of functional capacity in patients with CHF, because of a greater degree of objectivity. The different conclusions between the two studies may be related by the different population sample evaluated since the study by Varani et al. only included patients in NYHA class II and III.

A low degree of concordance (concordance, respectively, 41.7% for pVO2 and 35% for AT) existed between NYHA classification and the results of cardiopulmonary exercise categorized according to the Weber classification. In particular, it must be underlined, that AT has a limited discriminant value in patients with CHF. In fact, 43 out of 64 (67%) patients had a normal AT (>14 ml/kg per min) but only 16 were in NYHA class I, and nine were in NYHA class III–IV. Our results are similar to those by Van de Broeck et al. [21] and by Smith et al. [19]. In the last investigation, which included only male patients, however, the results of the cardiopulmonary exercise test were not stratified according to Weber classification and patients were arbitrarily subdivided into three groups (peak oxygen consumption>15ml/kg per min, between 10 and 15 ml/kg per min and <10 ml/kg per min) so that a direct comparison is not possible.

The concordance between NYHA classification and functional capacity evaluated by the 6-min walk corridor test was remarkably low (33%) in our patients, although the average distance walked was significantly different for each NYHA class group. Our results agree with those reported by SOLVD investigators [22] who found a large overlap among the distance walked in patients from all NYHA classes despite an overall significant difference in the distance walked by patients of different NYHA functional class. In particular, in the NYHA class II all the four levels of distance walked were represented by a similar percentage [22].

We found a statistically significant relation between pVO2 and the results of the 6-min walk corridor test (r=0.56). Our results are in agreement with those of other studies performed in patients with mild-to-moderate heart failure [15,33,34]. A statistically significant relation between the distance walked and pVO2 measured during maximal exercise test was reported also in patients with advanced CHF (mean pVO2 12.2 ml/kg per min) [16]. Roul et al. [17] found an overall poor relation between pVO2 and distance walked (r=0.24), however, the two variables showed a significantly closer relation (r=0.65) in patients walking less than 300 m. This observation suggests that in patients with more severe heart failure, the walk test more closely approaches the maximal exercise capacity of patients. The recent investigation by Lucas et al. [18], who reported an almost identical mean pVO2 during a sub-maximal bicycle ride at constant workload, that could be considered similar to that of walking, and during maximal exercise test in patients in Weber class D is in agreement with this hypothesis. In patients with less severe heart failure, the difference observed between mean pVO2 at constant workloads and pVO2 during maximal exercise test may be related to a different aerobic capacity needed to sustain low level exercise and that required for incremental workloads [35].

Results from the present study suggest that in patients with mild-to-moderate CHF none of the usually employed methods of functional evaluation give a definitive assessment of functional capacity of the cardiovascular system and a high degree of discordance exists among the results of different tests in the same patient.

As the NYHA classification (or Goldman’s Specificy Activity Scale) showed, at variance with pVO2 or the 6-min walk test, a significant relation with common indices of cardiac function ( LVEDD, LVFS, LVEF, cardiac output), it is likely that clinical classification and objective methods of evaluation explore different aspects of the functional limitation associated with CHF.

Results of the cardiopulmonary test and the 6-min walk test have a significant relation with mean pulmonary artery pressure and, noteworthy, with the peak expiratory flow rate thus, suggesting that actual cardiovascular performance is largely influenced by the impairment of pulmonary circulation and of pulmonary function. Previous investigations demonstrated an inverse relation between maximal oxygen consumption and pulmonary vascular resistance and right ventricular function [36,37] thus, suggesting that right ventricular function may be more important than left ventricular function in determining exercise capacity. Recently Butler et al. [38] clearly showed a significant inverse correlation between increasing values of pulmonary vascular resistance and VO2 and their respective cardiac output at peak exercise. Moreover, in patients with CHF, measures of pulmonary function were more closely related with peak exercise oxygen uptake than index of cardiac performance at rest [39,40]. Sustained improvement of functional capacity after veno-venous ultrafiltration associated with increased ventilation, tidal volume and dead space/tidal volume ratio [40], the parallel increase in distance walked during the 6-min walk test and in peak expiratory flow rate that we observed after administration of furosemide (data not published), the relation between and indexes of pulmonary function and the extravascular ‘lung water’ evaluated by a radiological scoring system [41] are consistent with this hypothesis.

The clinical and prognostic value of NYHA classification have been largely demonstrated, however, its usefulness is limited in patients with mild-to-moderate heart failure in which the discordance with methods of objective measurement of cardiovascular capacity is more evident as further demonstrated by our investigation. Moreover, NYHA classification does not allow accurate prognostic stratification in patients with advanced heart failure in order to select the patients candidate for heart transplantation. The 6-min walk test has been proposed as an objective method of evaluation of cardiovascular capacity and a potential substitute for pVO2 measurement. Several studies have demonstrated its prognostic value both in patients with mild-to-moderate [17] or severe CHF [16]. At present, however, the demonstration of interchangeability between the two methods are inconsistent [18] and the relatively weak concordance between the two methods shown in our investigation agree with this observation.

In conclusion, our results suggest that the 6-min walk test may be a useful screening test to evaluate functional capacity in symptomatic CHF that can be easily performed also in peripheral centers and in ambulatory patients. Patients in the lower performance class (distance walked at walk test<300 m) should be referred (age, absence of contraindications to heart transplantation) in this case for further diagnostic evaluation. Cardiopulmonary exercise test might be reserved to referral centers for evaluation of more compromised patients to be included in the list for heart transplantation.


   References
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 References
 

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