The radiographs were mostly unremarkable. There was a slight bulge in the region of the cranial
waist on the lateral view consistent with poststenotic dilatation of the proximal (ascending)
aorta.
The ECG had two criteria present for left ventricular hypertrophy. The R wave in lead II was
greater than 2.5 mV and the R wave in lead V2 (CV6LL) was greater than 3 mV. Many
dogs with severe subaortic stenosis have no evidence of left ventricular hypertrophy on an ECG.
This happens to be one that does.
Echocardiogram: Interventricular septal thickness (diastole) 1.5 cm, interventricular
septal thickness (systole) 1.6 cm, LV end-diastolic diameter 4.2 cm, LV end-systolic
diameter 2.8 cm, LV free wall thickness (d) 1.4 cm, LV free wall (s) 1.5 cm,
shortening fraction 34%, aortic root diameter : left atrial diameter 2:2.6 cm (normal).
There is a subaortic narrowing noted: the Ao area measures 3.5 cm² at the level of
the valve and the LVOT area measures 0.7 cm² at the area of the ring (these areas
should be comparable). Post-stenotic dilatation noted. Aortic velocity is turbulent with a
velocity of 5.5 m/s corresponding to a pressure gradient of 121 mmHg. Concentric LV
hypertrophy present with hyperechoic papillary muscles.
Dx: Severe subaortic stenosis. ECG findings and echocardiographic findings suggest myocardial
hypoxia, ischemia, and subendocardial fibrosis which is likely exacerbated by exercise.
Although no ventricular arrhythmias are noted, it is most likely that the syncopal episodes
are due to these (although inappropriate mechanoreceptor function and resulting bradycardia is
also a possible mechanism in these dogs.) This dog is at great risk of sudden death.
Rx: Atenolol 50 mg BID. If he continues to collapse on this dose, a Holter monitor is
recommended. Discontinue Lasix. Exercise restriction is recommended.
Discharge Instructions
Yankee had an echocardiogram, ECG, and chest x-rays today. He has severe subaortic stenosis
which is a narrowing below his aorta restricting blood flow out of the heart with each
contraction. This causes his heart to grow thicker and predisposes to arrhythmias. The
prognosis with this disease is very poor and he is at risk for sudden death. The atenolol
is an antiarrhythmic drug which can help decrease the potential for arrhythmias. Please give
him 50 mg (2 tablets) of atenolol twice daily. Please also discontinue the Lasix. If
Yankee collapses again we would recommend that he have a 24-hour ECG (Holter monitor)
performed.
Follow-Up
The referring veterinarian examined the dog again three weeks later. He had had two more
syncopal episodes — one when he became excited and one when he was resting. The referring
veterinarian increased the dose of atenolol to 50 mg every 8 hours and recommended that he
come back to UCD for a Holter monitor. This was not done. The last follow-up phone call to
the referring veterinarian (the owner could not be reached) indicated that Yankee had not had
any more syncopal events up until one week before the phone call, which was 3.5 months after
the initial visit. The referring veterinarian had urged the owner to make a follow-up
appointment. At the time this was last updated, this appointment had not been made.