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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 6, November/December 2018
342
AFRICA
Electrocardiographic criteria signifying left ventricular
hypertrophy and reduction of cardiothoracic index were most
notably seen in patients who received nos 21, 23 and 25
mechanical valves. By contrast, the least remarkable improvement
was observed in cases operated on with no 19 mechanical valves
(Table 3).
Discussion
This study was performed to compare the functional and
anatomical changes in patients who underwent AVR with
different-sized mechanical valves. Our results demonstrated
that improvements and anatomical changes were observed most
notably in patients that received nos 21, 23 and 25 valves.
Aortic stenosis causes left ventricular hypertrophy as an
adaptive response to increasing pressure. Persistence of this load
may impede myocardial contractility and pump function. Aortic
valve replacement may relieve the pressure overload and result
in reversal of anatomical and functional changes due to aortic
stenosis. These improvements can be linked to factors such as the
timing of surgery, type and size of the mechanical prosthesis, and
valvular pathology.
12
However, complete regression of myocardial
hypertrophy may not occur since the hypertrophic myocytes
may have undergone irreversible changes.
13
Our results indicate
that patients with higher residual gradients and increased left
ventricular end-diastolic pressures experienced a less remarkable
decrease in left ventricular mass.
Irreversible myocardial depression and fibrosis, which
develops as a consequence of long-term aortic stenosis must be
borne in mind before deciding on surgery. Symptomatic patients
who suffer from angina pectoris, dyspnoea or syncope benefit
more significantly from AVR and have prolonged survival after
surgery.
14
Even for asymptomatic patients, the risk of sudden
death and irreversible left ventricular dysfunction may be
prevented with surgery.
15
Type and size of the prosthetic valve as well as other peri-
operative factors may influence anatomical and functional
changes after AVR. De Paulis
et al
. reported a significant
reduction in LVM in patients operated on due to aortic stenosis.
16
Bioprostheses without stents and aortic allografts are expected
to provide a more remarkable reduction in LVH and left
ventricular function.
16
Maselli
et al
. suggested that residual gradient and
high pressure in the left ventricle were responsible for the
unsatisfactory reduction in left ventricular mass after AVR.
17
In the same study, homograft valves yielded more significant
reductions in LVMI.
17
In contrast to these reports, Christakis
et
al
. could not demonstrate any impact of the type of prosthesis
on regression of LVM.
18
Prosthetic valves without stents
provided optimal regression on LVM within one year of the
operation.
19
A better haemodynamic performance was achieved using
prostheses without stents than with bioprostheses and stents.
18
Gonzalez-Juanatey
et al
. reported that larger prostheses
resulted in a more apparent reduction in LVH.
20
Similar to
this study, our results indicate that most significant changes in
LVM occurred in the sixth month postoperatively. Variations
in the amount of regression in LVM in our patients receiving
nos 19, 21, 23 and 25 prostheses were 25, 26.7, 27.8 and 30.2%,
respectively.
Botzenhardt
et al
. demonstrated mean pressure gradients
of 11.5
±
3.8 mmHg for no 21 and 12.7
±
5.0 mmHg for no 25
valves.
21
However, they realised that haemodynamic performance
was not primarily influenced by valve size but more by sizing
strategy, and therefore the selection of a given valve size
according to the patient’s anatomy. Since the relationship would
be similar for all valve sizes, it was not surprising to observe
similar pressure gradients with different valve sizes.
A residual gradient after AVR may cause persistence of LVH
and lead to increased mortality rates in the late period.
22
Lund
et al
. postulated that LVMI was closely associated with survival
after AVR.
23
If the effective surface area of the prosthesis is less
than a normal valve, a mismatch between patient and prosthesis
occurs, and this may be an important determinant of residual
gradient and persistent LVH.
24
The role of the surgeon and the sizing strategy adopted
appear to be very important in exploiting or failing to exploit the
haemodynamic characteristics of the prosthesis.
25
For selection
of the appropriate valve size, most authors advocate the use
of valves larger than no 21.
26
Smaller valves may lead to a high
transvalvular gradient, even at rest. Selecting a larger valve
bears a greater risk of causing damage, specifically to the aorta
around the aortotomy. When selecting a larger prosthesis, it may
be necessary to take the valve off the holder and tilt it for proper
introduction into the root.
27,28
We determined that patients who received no 19 valves
experienced less regression of LVM, especially in the third
and fifth postoperative years. In all groups, changes were more
obvious in the sixth postoperative month, whereas these changes
became less notable after the first year.
Regression of LVMmostly happens in the early postoperative
period after AVR, and persistence of LVH and deterioration of
left ventricular diastolic function may be one of the underlying
causes of sudden death. Our findings revealed that all groups
displayed a significant improvement in ejection fraction in the
sixth postoperative month. However, changes were more obvious
in cases that received nos 23 and 25 prosthetic valves.
Cardiac hypertrophy on ECG displays a correlation between
voltage criteria and LVMI.
29,30
In parallel to our results mentioned
above, voltage criteria exhibited the most prominent changes
with valve nos 23 and 25, and the least change occurred in
patients receiving no 19 valves.
The amount of regression of LVM after AVR is related to
degenerative changes in the myocardium and decrease in left
ventricular reserve. These factors must be kept in mind before
deciding on surgical intervention for aortic stenosis. Moreover,
in addition to size and type of prosthesis, the aetiology of aortic
stenosis and timing of surgery must be considered.
The main limitation of our study was the distribution of
patients in the study groups. The four patient groups were
determined by the different valve sizes, and almost 80% of the
patients were in the two groups with valve sizes nos 21 and 23.
Conclusion
The results of this study indicate that mechanical valve replacement
should not be performed with small size valves because of the
higher residual gradient. Instead, mechanical valve replacement
with larger sized valves, together with aortic root enlargement
procedures appears to be a more appropriate option.