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Case 29
 | Tetralogy of Fallot without cyanosis at rest
(so-called "pink tet") |
| ECG: HR 220 beats/minute; normal sinus rhythm; wide, tall P waves
in lead II with a duration of
0.03-0.04s and an amplitude of 0.3mV; PR interval
= 0.06s; short, splintered QRS
complexes in lead II with a normal
duration of 0.03s and amplitude of 0.3mV; deep S wave
present in left chest
lead (V4); Mean electrical axis in the
frontal plane = 170degrees. |
| ECHO: Butorphanol was given IM for sedation
to facilitate cooperation for echocardiography. Marked
right ventricular concentric hypertrophy with a right
ventricular free wall thickness of 6mm
and a left ventricular free
wall thickness of 4mm. Large ventricular septal defect (VSD)
with laminar flow from the right ventricle and left
ventricle into the aorta; narrowed
right ventricular outflow tract with malpositioning
of pulmonic valve and pulmonic stenosis; highest
velocity recorded across pulmonic valve region = 5.4
m/s (pressure gradient of 117;
therefore approximate RV and LV pressure of 140 mmHg
assuming the systolic pulmonary artery pressure is 20 to 25 mmHg).
Overriding aorta visualized. |
| Thoracic radiographs: two view thorax:
enlarged heart (vertebral heart
score=10.25); right
heart enlargement; hypoperfusion of the pulmonary
vasculature with diminutive caudal lobar vessels and pulmonary arteries. |
| PCV:38%; total protein=7.4
|
| Arterial blood gas: pH 7.4,
PCO2 - 30 mmHg,
PO2 - 36
mmHg, K - 4.5 mEq/l, Na -
150 mEq/l,
Ca - 1.36 mmol/l, oxygen saturation 64%, acid base:
HCO3 - 17.1 mmol/L, tCO2 - 18 mmol/L, base deficit
- 6.8 mmol/L |
| Conclusions:
The ECG findings are consistent with right ventricular enlargement
although the limb lead axis could also be consistent with a so-called
posterior fascicular block. The deep S wave in V4
is consistent with right ventricular enlargement.
Echocardiographic
findings documented the presence of tetralogy of Fallot
with right ventricular outflow tract narrowing and/or
pulmonic stenosis, an overriding aorta,
a large ventricular septal defect, and
right ventricular concentric hypertrophy of
6mm. Right-to-left
shunting of blood flow was present with laminar flow evident from
both the right and left ventricles through
the large
VSD into the aorta.
An arterial blood gas sample obtained from
the femoral artery revealed a
PO2 of 36 mmHg. This documents
severe hypoxemia due to shunting of venous blood into
the arterial circulation. Clinically Nimbus
was not cyanotic at rest. When severely stressed by
restraint (as she was during femoral artery puncture for
blood gas analysis), she did progress to open-mouth breathing
with increased abdominal effort and cyanosis.
This resolved within minutes with rest.
The PCV of 38% is in the normal range for a cat of her age
(average normal is 41%);
normal PCV values are usually
attained by four months of age. The normal PCV verifies
that Nimbus does not have hypoxemia severe enough to cause polycythemia at
most times in her life. Clinically significant polycythemia does not occur
until the arterial oxygen tension decreases into the 30 to 50 mmHg range. With
stress the arterial oxygen tension did decrease into this range and Nimbus did
turn blue. However, when not stressed she was pink (see the picture of her
oral mucous membranes on the first page). |
| The diagnosis of tetralogy of Fallot is rare in cats and
the prognosis for
Nimbus will depend on whether or not her disease
progresses over time. At this time the
owner has been advised to monitor for development of signs of increased
respiratory rate or effort with play or stress, to have a PCV taken every 3
months by her referring veterinarian, and to return
for a progress check in 6-7 months. Client was also instructed to call Dr.
Wess if the PCV is greater than 50%, indicating worsening polycythemia.
|
| Thank you for bringing Nimbus to see us today. She is a darling kitty.
As we discussed with you, we found that she does have a congenital heart
defect called tetralogy of Fallot which consists of four lesions of the heart:
the narrowing of the outflow tract of the right ventricle (pulmonic
stenosis), the ventricular septal defect (the hole between the right and left
ventricles), the malpositioned aorta, and the thickening of the muscle of the
right ventricle. |
| What this means is that some of the venous blood from the right heart that is
supposed to go to the lungs is going out into the circulation to her body instead.
That means that her blood is not carrying as much oxygen as normal (she is at
about 35-40 mmHg when she is stressed instead of 100 mmHg oxygen in her blood).
|
| We would like you to observe her for any development of clinical signs,
which could include open-mouth breathing, panting, increased abdominal effort
of breathing, or purplish or bluish color to her gums or tongue. Exercise,
stress, or exuberant play may make these signs worse. If she appears to be
having difficulty breathing that does not get better with rest, please call
your veterinarian or us. |
| In order to monitor her condition we recommend that you have your
veterinarian check her PCV (packed cell volume) every 3 months. This is a
measure of how many red blood cells are in her blood. If the PCV is greater
than 50% please call us. Today her PCV is normal at 38%.
|
| We would like to see her back for a recheck cardiac ultrasound in 6 or
7 months. |
| Thank you for bringing her here; she is a cutie and we enjoyed meeting
her. |
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