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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 2, March/April 2019
114
AFRICA
treatment. The data also suggest that, alarmingly, as few as 50%
of patients succeed in maintaining target INR values over the
course of treatment, and as many as 22–33% of patients newly
prescribed preventative anticoagulants discontinue the treatment
within the first year.
5
Similar challenges exist in the treatment of heart failure (HF),
which affects 10–20% of the population over 60 years of age. One
in five patients hospitalised for HF is rehospitalised within the
first month after discharge, and one in three within the next two
months; 80% of HF hospitalisations are rehospitalisations due
to exacerbation of symptoms. Statistics on one- and five-year
mortality rates from HF reveal similar findings.
6
One significant
cause of rehospitalisation is non-adherence to treatment.
7
Adherence measurement methods
Adherence measurement methods can be broadly defined in
two categories: direct and indirect. Direct methods include
electronic monitoring systems, pill counting, and measurement
of medication use, drug concentrations in bodily fluids and
serum activity of selected biochemical markers present in the
medication.
8
Indirect methods include surveying and observation, with
discussions regarding the way in which the prescribed medication
is taken. Indirect observation methods commonly include
subjective measures, such as self-reported questionnaires and
scales. Apart from pharmaceutical adherence, many of these
methods also help identify difficulties in taking medication,
patients’ beliefs and attitudes towards the treatment, or
their knowledge of the disease and its treatment. Adherence
questionnaires can be generic, that is, suitable for the assessment
of adherence in a variety of chronic diseases, or they can be
disease-specific.
Self-reported questionnaires are an alternative to other
measures, although they have a number of potential limitations
related to, for example, the patients’ understanding of the
questions and willingness to provide answers, which may affect
the results. The choice of questionnaire is also dependent on the
availability of a version adapted to a given national setting. Some
questionnaires only measure pharmaceutical adherence, while
others allow researchers to evaluate the entire treatment process.
Despite the risk of overestimating patient adherence or
non-adherence, the use of questionnaires is the cheapest and
simplest method, which also provides additional information on
the causes of non-adherence. Most questionnaires capture data
on medication dosage from the start of treatment, throughout
the treatment period, and up to the end of treatment.
In 2014, 43 adherence scales were described, which can be
grouped into five categories, evaluating: (1) medication adherence
only, (2) medication adherence and barriers to adherence, (3)
barriers to adherence only, (4) patient beliefs about adherence
only, and (5) patient beliefs and barriers to adherence.
9
Despite
the relatively large number of questionnaires available, no gold
standard for adherence measurement has been established.
The purpose of this article was to review the validated
instruments available for measuring adherence to treatment in
selected cardiovascular diseases, identify the ones that are most
commonly used, and offer the best psychometric properties.
We chose to focus on hypertension, atrial fibrillation and heart
failure due to their increasing epidemiology and the fact that the
data from the literature show a high level of non-adherence.
At present, none of the available methods can be considered
a gold standard for adherence assessment. There are many
questionnaires available in the medical databases, but the
selection of a method to monitor adherence should be based on
the individual attributes and goals/resources of the study or the
clinical setting. We chose the ones that are most commonly used
in research.
Adherence measures applicable to hypertension
The Morisky Medication Adherence Scale is the most commonly
used questionnaire worldwide. Its original version, developed by
Morisky, Green and Levine (MGL) in 1986, comprised four items
and evaluated adherence to medication in hypertensive patients.
The original questionnaire had only satisfactory psychometric
properties (alpha reliability
=
0.61).
The scale was translated into Portuguese and tested on
hypertensive patients, showing satisfactory psychometric
properties as an instrument for adherence measurement (alpha
reliability
=
0.73). Another attempt to adapt it, for patients
at risk of atherosclerosis, showed the scale could be useful in
evaluating non-adherence and its causes, but not in elderly
patients (Cronbach’s
α
=
0.47, internal correlations 0.11–0.26).
The MGL questionnaire was used for adherence measurement
in a number of chronic diseases: asthma, chronic obstructive
pulmonary disease (COPD), diabetes, tuberculosis, leukaemias
and kidney failure; and with a number of treatments: immune
treatment for allergies and hay fever, and treatment with calcium,
vitamin D, acenocoumarol and others.
In 2008, the eight-item Morisky Medication Adherence
Scale (MMAS-8) was developed, adding four items related to
the circumstances of adherence to the previous four-item MGL
test.
10,11
The cultural adaptation of the questionnaire into Polish
and its validation showed that the adapted questionnaire had
good psychometric properties (Cronbach’s
α =
0.808), similar to
the original (Cronbach’s
α
=
0.83).
12
The questionnaire has also
been translated and adapted into French (Cronbach’s
α
=
0.54),
Thai (Cronbach’s
α
=
0.61), Farsi (Cronbach’s
α
=
0.697) and
Brazilian Portuguese (Cronbach’s
α =
0.682).
Based on the criteria used, the usefulness of the MMAS
as a source of information on BP control in clinical settings
was confirmed. There was a significant correlation between
the adherence scale and BP control (
χ
2
=
6.6;
p
<
0.05). High
adherence of the patients studied was expressed as a score of
8, medium adherence from 6 to
<
8 and low adherence
<
6. The
scale comprising eight items proved to be a reliable instrument
(
α
=
0.83), which significantly correlated with BP control (
p
<
0.05).
13
Another commonly used adherence measure is the Hill–
Bone Compliance to High Blood Pressure Therapy Scale,
which comprises items related to both medication adherence
in hypertension, and lifestyle modifications. Its purpose is to
assess behaviours centred around taking medication, dietary
sodium restriction, and regular follow ups among hypertensive
patients. In its Polish version, the Hill–Bone scale showed very
good psychometric properties with regard to reliability, validity
and acceptability. The Cronbach’s
α
for the Polish version
was 0.851, similar to the original (0.74), and to other adapted
versions: Turkish (0.72), South African (0.77), Malaysian (0.64)