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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 6, November/December 2018
AFRICA
339
Methods
The study was conducted in accordance with the principles of the
Helsinki Declaration. It was approved by the local institutional
review board (17/08). Informed consent was obtained from all
patients with regard to serious aortic stenosis for AVR operation.
This cohort study was performed in the cardiovascular
surgery department of a tertiary care centre on 98 patients with
serious aortic stenosis. They underwent AVR surgery between
March 2001 and June 2008. The inclusion criterion was severe
symptomatic aortic stenosis.
Exclusion criteria were a previous history of coronary or
other cardiac valvular surgery, left ventricular ejection fraction
<
30%, contra-indication for the placement of a bioprosthetic
valve, and unwillingness to participate in the study. A total of
six patients were excluded since four died due to cardiac and
multiple organ failure in the postoperative period, and two cases
were lost to follow up.
Patients were operated on using Bileaflet (St Jude Medical,
St Paul, MN, USA) and Carbomedics (Sorin Group, Milan,
Italy) mechanical valvular prostheses and they were divided into
four groups according to the size of the valves. Demographic
and clinical data were recorded, and pre- and postoperative
functional capacities were determined with regard to New York
Heart Association (NYHA) functional class.
5
Pre-operative
evaluations consisting of echocardiography, electrocardiography
and telecardiography were performed to determine the
anatomical and functional condition of the left ventricle.
Left ventricular ejection fraction (LVEF), aortic valve area
(AVA), peak aortic valve gradient (PAG), mean aortic valve
gradient (MAG), left ventricular end-systolic and end-diastolic
diameters (LVESD, LVEDD), thickness of the posterior wall
(PWT) and interventricular septum (IVST), as well as left
ventricular mass (LVM) and mass index (LVMI) were measured.
Durations of aortic cross-clamp, cardiopulmonary bypass,
intensive care unit stay and hospitalisation were noted.
Patients were re-assessed postoperatively regarding clinical
and echocardiographic findings in the sixth month, and first,
third and fifth years. Four patient groups were created according
to the mechanical valve sizes used. Comparisons of pre- and
postoperative results, as well as postoperative changes, were
carried out both within and between groups.
Transthoracic echocardiography was performed using a
3-MHz transducer of the SyncMaster 550b Vivid 3 device
(Samsung Electronics Co Ltd, San Jose, CA, USA). Continuous-
wave, pulsed-wave and colour Doppler as well as M-mode
images were obtained from two-dimensional views, according to
the criteria defined by the American Echocardiography Society
guidelines.
6
Left parasternal, apical, subcostal and suprasternal images
were routinely taken pre-operatively. Anatomical variables were
measured and noted.
M-mode echocardiography was used to assess end-systolic
and end-diastolic diameters in addition to the thickness of the
interventricular septum. The average of three heart beats was
used for patients in sinus rhythm, while six beats were taken into
account for cases with atrial fibrillation. Aortic valve area was
calculated using the continuity equation.
7
Estimation of LVM was done using the modified Devereux
and Reichek formulae:
8
LVM (g)
=
0.8
×
1.04
×
[(LVEDD
+
IVS
+
PWT)
3
– LVEDD
3
]
+
0.6
where LVEDD
=
end-diastolic diameter of the left ventricle, IVS
=
interventricular septum, PWT
=
posterior wall thickness.
8
Then left ventricular mass index (LVMI, g/m
2
) was obtained
with the following formula: LVM/body surface area.
Trans-valvular pressure gradients were calculated via the
simplified Bernoulli equation using values obtained from
Doppler echocardiography measurements (continuous wave,
pulsed wave and colour modes). The average pressure gradient
was the average of all gradients during the whole flow period,
and it was calculated from the area below the flow curve.
9
Ejection fraction of the left ventricle was assessed by the
modified Simpson’s method.
10
Electrocardiography: the majority of patients with aortic
stenosis exhibit voltage changes due to left ventricular pressure
load. Patients operated on with different-sized mechanical valves
were compared with regard to ECG criteria.
11
Telecardiography: the size and shape of the heart, as well as
the position of the great vessels and pulmonary vascularisation
should be considered in the evaluation of congenital and acquired
cardiac diseases. Cardiothoracic ratio is the maximal cardiac
diameter divided by the maximal horizontal thoracic diameter
(inner edge of ribs/edge of pleura).
11
A normal measurement
should be less than 0.5. Cardiothoracic ratios were compared
pre- and postoperatively.
All patients were operated on under standard general
anaesthesia techniques. A central venous line was provided by
placing an 8.5-F percutaneous catheter into the right internal
jugular vein (Swan-Ganz catheter, 7-F Multiflex thermodilution
catheter, Abbott Critical Care Systems, North Chicago, IL,
USA). Monitoring of the central venous, right atrial, right
ventricular, pulmonary arterial and pulmonary artery wedge
pressures was done.
For anticoagulation, heparin was administered at a dose of
300 U/kg. After a median sternotomy, arterial cannulation was
performed via the ascending aorta, while venous cannulation was
accomplished with a ‘two-stage’ cannula through the right atrial
appendix. Moderate hypothermia (rectal temperature: 28–30°C)
was provided. Hypothermic blood cardioplegia, applied directly
antegradely or retrogradely through the coronary sinus, was used
for protection of the myocardium. An oblique aortotomy was
performed in all patients. Advanced calcification was observed
in 20 patients who underwent decalcification.
Bileaflet mechanical valves were implanted as the central
axes of the valves were parallel to the septum and separated 2/0
Ticron pledgeted sutures (Covidien Ltd, Dublin, Ireland) were
used for this purpose. Pledgets were placed in the sub-annular
plane in 24 patients who had a weak aortic annulus or who
underwent decalcification.
The Nicks procedure for aortic root enlargement was performed
in 10 patients with a narrow aortic root. Prosthetic valve no 19 was
used in four patients, while no 21 and 23 valves were preferred
in two and four patients, respectively. In three patients in whom
no 19 and 23 prosthetic valves were used, pledgets were placed
outside the aortic wall in the non-coronary annular region.
Composite graft replacement using the Buton–Bentall technique
was performed in three patients due to post-stenotic dilatation.
An aortotomy was repaired using two pledged 4/0 non-absorbable
monofilament continuous sutures. Numbers 19, 21, 23 and 25
prosthetic valves were therefore used in eight (8.6%), 38 (41.3%),
40 (43.4%) and six (6.5%) patients, respectively.