Clinical classification Total scale score
3.4.3 Additional measures of executive function
The cognitive domain of executive function has been understudied in the HF population to date.
This is relevant to patients with HF, as “executive function” is an umbrella term used to describe various cognitive processes involved in the handling of novel situations. It is a faculty for recognising these situations, processing information and formulating plans accordingly.
This is obviously key to patients involved in symptom recognition and self-management.
Individual “bolt-on” assessments of executive function were therefore added to the other standard measures of global and domain-specific cognition.
3.4.3.1 Wechsler letter number sequencing
The Wechsler Adult Intelligence Scale (WAIS) intelligence quotient (IQ) tests are the primary instruments used to measure adult intelligence in clinical practice. The original WAIS (Form I) was published in 1955 by David Wechsler and has been updated over recent years.169
The current version of the test, the WAIS-IV, was released in 2008 and is composed of 10 core subtests one of which is the test of Wechsler Letter Number Sequencing (WLNS). This subtest assesses attention and executive function by asking examinees to repeat sequences of number and letters in both numerical and alphabetical order (see appendix VII). The WAIS-IV has been standardised on a sample of 2,200 people in the United States ranging from 16 to 90 years of age.170 In a normal distribution, the IQ range of one standard deviation above and below the mean is where approximately 68% of all adults would fall.171
3.4.3.2 Trail making test parts A and B
The Trail Making Test (TMT) is one of the most popular neuropsychological assessment tools used to assess speed of processing, mental flexibility and executive function. The TMT consists of 2 parts; A and B. TMT-A asks an individual to draw lines sequentially connecting 25 encircled numbers. The requirements are similar for TMT-B except the participant now has to alternate between numbers and letters. The score on each part represents the length of time required to complete the test (see appendix X).
Performance on the TMT varies with age and years of education but not gender.175 Based on a study of 911 community dwelling individuals normative values were therefore stratified into 11 age groups (18-89 years) and 2 education levels (0-12 and > 12 years) allowing more accurate interpretation of these scores and translation into clinical practice.172 These normative values are available in appendix XI.
3.4.3.3 Controlled oral word association test
Original time-limited, verbal fluency tests date back to the Thurstone’s Word Fluency Test, which formed part of the primary mental abilities test. This originally asked participants to write words beginning with a specific letter over a relatively long period of time e.g. 5 minutes.
This has gradually evolved and in the current version this test of phonemic verbal fluency and executive function records the number of words beginning with the same designated letter said by the participant in one minute (appendix VII). The name of the test was changed to controlled oral word association (COWA) test to avoid confusing the phrase “word fluency”.
The letters F, A and S have continued to be used as a measure of verbal fluency in the neurosensory centre comprehensive examination for aphasia.173
As education may play a role and because gender differences have been reported (with females performing at a superior rate to age-matched males) a normative sample stratified according to age, education and sex was examined in a study by Ruff et al in 1996.174 The total sample of 360 normal volunteers ranged in age between 16 and 70 years and in education from 7 to 22 years. Care was taken to ensure the population was heterogeneous with respect to age and education. To assess test-retest reliability, 30% of the sample was retested after a 6 month delay. A three-way analyses of variance (age x gender x education) was carried out on the mean number of words for all three letters. Age had no significant effect. However, gender moderated the effect of education on the number of words produced. The interaction of gender and education was ordinal, with the effect of years of education positively predicting COWA performance for both men and women. Therefore the effect of education was significant (p<0.0001), and differences due to education alone accounted for a greater proportion of total
variance (8%). The current accepted cut-off scores for COWA (F, A & S) are shown in table 3-5.
Table 3-5: Normative values for F, A, S stratified for age and years of education Age 16-59 years Age 60-79years Age 80-95years
3.4.3.4 Animal naming test
Semantic fluency is another method of assessing verbal fluency. Individuals are asked to generate names from a specified category in one minute and the category of animals is most frequently employed (see appendix VII). Tombaugh et al stratified normative values by age (16-59, 60-79 and 80-95 years) and years of education (0-8, 9-12 and 13-21) in 735 community dwelling volunteers.175 Unlike with the phonemic verbal fluency tests, age accounted for more variance than years of education in this assessment tool (education 13.6% vs. age 23.4%) and gender was found to account for less than 1% of the variance. Table 3-6 shows the accepted normative values for the animal naming test stratified by age and years of education.
Age 16-59 years Age 60-79years Age 80-95years
3.4.3.5 Frontal assessment battery
The frontal assessment battery (FAB) is a bedside tool that takes approximately 10 minutes to administer and is used in the assessment of executive function. It consists of six questions which explore both cognitive and behavioural domains under the control of the frontal lobes.
The FAB was initially designed in 2000 in a study of 42 normal subjects and 121 patients with various degrees of frontal lobe dysfunction.176 They found a cut-off score of 12 had a sensitivity of 77% and a specificity of 87% in differentiating between frontal lobe dementia and Alzheimer’s dementia. A copy of the FAB is shown in appendix XII.
3.4.4 Measure of pre-morbid intelligence quotient 3.4.4.1 Wechsler test of adult reading
The Wechsler test of adult (WTAR) reading provides a tool for estimating premorbid intellectual functioning. When assessing individuals for possible CI, it is necessary to know whether their current cognitive state represents a decline from their pre-morbid level. The inclusion of a marker of pre-morbid IQ is something which has been neglected in current HF and cognition literature to date.
The WTAR is based on a reading-recognition paradigm, requiring the reading and pronunciation of words that have irregular phonetic translation but not requiring knowledge of word meaning. Examinees are given a card with 50 words written on it. They are asked to read these words aloud and given one mark for each word pronounced correctly (see appendix XIII). The use of words with irregular pronunciation minimises the assessment of the examinee’s current ability to apply standard pronunciation rules and maximises the assessment of the examinee’s previous learning of the word. Pronunciation guidance is given