Chapter 41
IDIOPATHIC HYPERTROPHIC SUBAORTIC STENOSIS (IHSS) Idopatic Hypertrophic Subaortic Stenosis involves a cardiomyopathy where thickening of the interventricular septum and left ventricular outflow tract determine obstructive condition during stystole.
The disease seems to be inherited in approximately 45% of these patients with an autosomal dominant pattern. There is, however, a large number of patients where no familial transmission can be demonstrated.
The disease is more prevalent in males and in particular, in those with good athletic physical development.
It is very rare in infants, being more prevalent in adolescents and young adults. Not unusually, the disease can be associated with other different congenital heart malformations.
The obstructive nature of this condition is a consequence of the aforementioned septal hypertrophy and the mitral valve leaflet opening which occurs in the mid systole. Significant mitral insufficiency is not uncommon. Left ventricular hypertrophy of different magnitude is the rule.
Hyperkinetic heart condition is present in the majority of these patients.
The obstructive nature of this complex typically increases with physical exertion.
The patient gives a first impression many times of being just a "common" mitral insufficiency or even VSD.
CLINICAL PICTURE AND PHYSICAL FINDINGS - Dyspnea on exertion, palpitations and paroxysmal nocturnal dyspnea (decreasing order of frequency).
- Chest pain and syncope are not unusual in severe cases and many times occur with physical exertion.
- Left ventricular hypertrophy. Left ventricular lift.
- Double systolic impulse in apex (bisferiens left ventricular impulse).
- Palpable "a" wave in many cases.
- Large number of patients present a low precordial systolic thrill.
- Mid and late systolic ejection "aortic" murmur along the left
external border (which is increased by exertion and amyl nitrate).
The murmur is poorly transmitted to the neck. - Bisferieus periphral arterial pulse (pulse rises in contrast to aortic stenosis).
- Murmur of mitral regurgitation if mitral insufficiency is present.
- Protodiostolic gallop is audible in 50% of patients.
Supraventricular arrhythmias may appear (junctional rhythm, atrial flutter and atrial fibrillation) as a consequence of left atrial failure (they imply a poor prognosis).
The typical carotid pulse is characterized by sharp rise, mid systolic notch and a secondary evaluation during systole.
Important "a" wave of atrial contraction in the jugular pulse recordings.
ELECTROCARDIOGRAM It varies from normal to significantly abnormal.
Left ventricular hypertrophy is common.
Often has left anterior hemiblock.
Q waves in anteriolateral leads which can simulate recent myocardial infarction is not unusual.
Many times deep Q in II, .111, AVF with ST segment elevation can be seen.
ROENTGENOGRAM Left ventricular hypertrophy.
Aortic dilatation is unusual. The finding of dilatation at that level correlates more oftenly with aortic valvular or subvalvular stenosis.
HEMODYNAMICS AND ANGIOGRAPHY Normal or moderate elevation of right pulmonary artery pressure.
Prominent "a" wave in right atrial pressure which sometimes may surpass 20 mm Hg.
Pull back pressure across the outflow tract of the left ventricle may demonstrate a subaortic gradient. Many times vasoactive products (Isuprel) need to be used to demonstrate this gradient.
Isometric exercise usually significantly increased subaortic gradient.
The arterial pulse pressure will not show the normal post extrasystolic pressure augmentation.
Digitalis, isoproterenol, amyl nitrate and nitroglycerin intensify the gradient of obstruction. Upright posture, Valsalva maneuver and pacer induced tachycardia will have the same action.
Propranolol, phenylepherine and methoxaine reduce the outflow tract obstruction.
The left ventricular ejection time is usually prolonged and proportional to the degree of gradient. Shorter upstroke time is seen in contrast in the aortic pressure recording.
LEFT VENTRICULAR ANGIOGRAM The left ventricular angiogram may usually show thickening of the ventricular wall with small left ventricular cavity.
The most prominent morphologic change is the indentation in the right inferior margin of the outflow tract, which results from the asymmetric hypertrophy of the intraventricular septum.
During the systole and in a lateral projection, approximation between the asymmetric septum and the anterior mitral valve leaflet will be seen.
Due probably to the distortion of the mitral subvalvular apparatus,mitral regurgitation of different magnitude is almost the rule in patients with significant IHSS. Most of the time, however, the incompetence tends to be mild and occurs in early systole.
ECHOCARDIOGRAPHY Echocardiography is useful in demonstrating the functional left ventricular outflow tract obstruction.
The sonogram, if done by an expert echocardiographer, will show the asymmetric hypertrophy of the septum, the thickening of the ventricular wall and the progressive systolic approximation of the intraventricular septum and the anterior mitral leaflet.
The hyperdynamic condition of the left ventricular contraction is rather characteristic.
Systolic bulging of the mitral valve, against a thickened intraventricular septum is the classical finding in this pathology.
Pseudo-IHSS motion can be observed, however, in echocardiograms of patients with aortic insufficiency and atrial septal defect.
MEDICAL AND SURGICAL TREATMENT Unless the patient presents with atrial flutter or atrial fibrillation, no digitalis should be administered. Nitroglycerin and strong diuretics can be troublesome.
Propranolol is the drug of choice for chronic therapy, diminishing the heart rate, hence the outflow obstruction, and reducing the frequency of syncope, angina pectoris and arrhythmias. If congestive heart failure occurs, Propranolol will not improve such decompensation.
In case of syncope, rapid administration of Phenylephrine or Methoxamine to relieve the obstruction is advised.
In case of congestive failure, surgical treatment is advisable as in any case with subvalvular gradient higher than 60 mm Hg.
The surgical procedure is done via the ascending aorta, right or left ventricle, and consists in a partial resection of the hypertrophied septal muscle in the left ventricular outflow tract.
The operative mortality should be lower than 5% and in a few cases the patient can be left with a permanent complete A-V block.
Electrocardiogram of a 17 year-old patient with Idiopatic Hypertrophy. Subaortic Stenosis discovered after having a syncopal attack during a football game.
Typical pressure recordings in case of idiopatic hypertrophyc subaortic stenosis (IHSS). Left ventricular gradient at outflow tract level can be noted. An initial rapid rise in aortic pressure is characteristic with a second systolic rise which is not clearly depicted in this particular pressure recording. The shaded area indicates a pressure chamber between the subaortic stenosis and the semilunar valves.
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