CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 1, January/February 2014
AFRICA
5
to cardiovascular disease.
13
Dipping, which can only be assessed
using ambulatory monitoring techniques, correlates better with
left ventricular mass index (LVMI) in end-stage renal disease
than office-based blood pressure measurement.
14,15
There have been calls for the routine use of ambulatory blood
pressure monitoring (ABPM) in clinical studies of CKD
13,16
and
indeed, for investigations into the utility of ambulatory CASP
in clinical practice.
17,18
Combining both ambulatory and central
pressure measurements is an attractive strategy, but until recently
has not been technically possible.
A non-invasive wrist watch-like device, BPro with A-Pulse
CASP software (HealthStats, Singapore) was recently approved
by the US Food and Drug Administration (FDA: K072593) for
the measurement of CASP as well as ambulatory blood pressure.
It is a small, wrist watch-like, cuffless monitor which obtains
radial pressure waveforms by applanation tonometry. BPro has
the ability to measure ambulatory CASP and although not yet
commercially available, the manufacturer is able to convert data
into ambulatory CASP using the same software.
As part of a recently published study on vascular calcification,
19
we sought to prospectively evaluate whether the presence of
vascular calcification had any relationship with ambulatory
CASP in our young CKD-5D cohort using the BPro
®
radial
pulse-wave acquisition device. We also sought to determine the
utility of inter-dialytic office brachial and central blood pressure
measurements in predicting ambulatory parameters.
Methods
The study was approved by the Research Ethics Committee of
the University of Cape Town, SouthAfrica. The full methodology
has been published elsewhere,
19
but briefly, cases were selected
if they were on maintenance dialysis of three months or longer
duration and were able to sign informed consent. Seventy-five
prevalent dialysis patients 18 years or older were enrolled from
Groote Schuur Hospital, Cape Town.
Patients were excluded if they were pregnant or planning a
pregnancy, had sustained arrhythmias or prior coronary stenting
or bypass. One patient was excluded due to loss to follow
up so the final case sample was 74 participants. Clinical and
demographic data were collected and ethnicity was self-reported.
Ambulatory and office blood pressure monitoring: the
BPro
®
radial pulse wave acquisition device and A-pulse CASP
®
software (HealthStats, Singapore) system uses an N-point
moving-average method to non-invasively derive CASP from the
radial arterial pressure waveform. It has been validated against a
generalised transfer function method using CAFE study data as
well as central aortic pressures recorded
in vivo
at the aortic root,
using a Millar’s SPC–454D tonometer (Millar’s instruments,
Texas USA).
20
The device also recently compared favourably
to the widely used non-invasive SphygmoCor system (AtCor
Medical, Sydney, New South Wales, Australia), with good
agreement compared to invasively determined CASP.
17
For blood pressure determination, the BPro™ has been
validated against the Association for the Advancement of
Medical Instrumentation and European Society of Hypertension
(ESH) protocols and passed both validations.
21
The BPro™
records pressure wave forms calibrated to the brachial blood
pressure and samples up to 96 × 10-second blocks of time over
24 hours. This provides a 24-hour profile and summary of an
individual’s systolic, diastolic and mean arterial pressures via the
use of BPro SOFT
®
software.
Practically, the device was applied on the non-dominant arm
or that which did not contain an AVF on the inter-dialytic day
for haemodialysis patients or at a routine visit for prevalent
dialysis patients. The device was then calibrated to office blood
pressure – brachial blood pressure obtained via use of the
MC3000 oscillometric device (HealthStats) according to the
recommended ESH protocol.
22
The manufacturer was able to
convert the ABPM data into ambulatory CASP readings since
the data are acquired in the same way for both.
Cardiac CT and coronary calcium score: images were
acquired using the Philips Brilliance 64-slice MDCT scanner.
A standard protocol was used as follows: tube voltage, 120 kV;
tube current, 55 mAs; detector collimation, 40
×
0.625 mm;
gantry rotation, 400 ms. CT data were transferred to the Philips
Extended Brilliance Workstation Version 4.0.2.145 for analysis
and coronary calcium score was calculated with the Agatston
algorithm.
23
All scans were evaluated by a single experienced
radiologist (SM) and the intra-reader variability was tested and
was below 10%.
Abdominal X-ray and abdominal aortic calcium score: a
standard technique of exposing the lateral lumbar spine in the
standing position (with 100-cm film distance, 94 KVP, and
33–200 mAs) was used. Calcific deposits in the abdominal aorta
were scored as described by Kaupilla,
24
by a single experienced
clinician (RF) blinded to clinical data and coronary calcium
score.
Echocardiography: assessment of the left ventricular mass
was done via use of M-mode echocardiography and this
was calculated using the Penn convention.
25
Left ventricular
hypertrophy was defined as
>
125 g/m
2
in males and
>
110 g/m
2
in females as per ESH guidelines.
26
All scans were obtained and
evaluated by a single experienced cardiologist (AL).
Statistical analysis
Normality was determined with the Shapiro–Wilk test.
Continuous variables are expressed as mean
±
SD or median
and inter-quartile range (IQR) and compared with the two-tailed
independent Student’s
t
-test and Mann–Whitney test as
appropriate. Dichotomous data are presented as percentages and
compared with chi-square tests. All analyses were conducted
using Stata 12.0 statistical software (College Station, TX, USA).
Results
Table 1 shows the baseline characteristics of all patients. Overall,
only 27 patients (38.6%) in the cohort had a coronary calcium
score
≥
1, and 26 (35.6%) had an abdominal aortic calcium
score
≥
1. The median coronary calcium score in those with
coronary calcification was 141 (IQR
=
55–619) and in those
with abdominal aortic calcification, the median abdominal aortic
calcium score was 6 (IQR
=
1–10). Table 2 shows the baseline
characteristics for all subjects with and without coronary and/or
abdominal aortic calcification.
Both coronary and aortic calcium presence failed to show
any association with CASP (
p
=
0.2 and 0.4, respectively).
There was no difference when the ratio was compared in those
with the highest versus lowest quartiles of coronary and aortic
