The cardiovascular system is a host to a broad spectrum of anomalies which if left untreated or undetected can lead to premature loss of life. To manage these diseased and pathologic states one needs to undertake an equally effective medical and aesthetic management. This paper will focus on the diagnosis and implications of Idiopathic Hypertrophic Subaortic Stenosis (IHSS). As a rare clinical diagnosis, it lies in the more severe spectrum of cardiovascular disorders which are currently among the leading causes of mortality. Idiopathic Hypertrophic Subaortic Stenosis is the most common cardiac genetic disease that is autosomally dominant. It causes a mutation in the encoding of proteins in the cardiac sarcomere. Sarcomeres are the contractile elements of the cardiac myocytes and when these cells become hypertrophied they increase in size and can alter cardiac functioning. Under microscopic evaluation, the cellular matrix of the affected tissues display an altered arrangement separated by large clefts and contains fluorescent material that is presumably norepinephrine. The hypertrophied myocardium also causes a disruption of the electrical conduction pattern of the heart thereby increasing the likelihood of arrhythmias.Epidemiology:
IHSS is a relatively rare diagnosis that affects approximately 1 to 2 people in every 1,000 or less than 200,000 people in the US and affects all age groups. According to current statistics, the prevalence of IHSS is more like 1 in every 500 because many cases are undiagnosed. However, with the general population undergoing many surgical procedures per year, it is conceivable that many of these undiagnosed patients are likely to be countered at least before the conditions reach the terminal stage. Recently, IHSS has been classified under the more general diagnosis of hypertrophic cardiomyopathy or asymmetric septal hypertrophy due to the fact one may have hypertrophy with all the negative implications but not necessarily a stenotic area causing an outflow obstruction. Some populations are more susceptible to IHSS than others. These include athletes, and those who perform heavy manual labor. IHSS has been identified as one of the most common causes of "sudden death" in the pediatric and young adult populations (Anesthesia and co existing disease). It is the leading cause of death during athletic activities for those affected. Disregarding the age of the individual, if left untreated or undiagnosed these patients may develop lethal cardiac arrhythmias that can increase their propensity to experience "sudden death" (anesthesia and coexisting disease). Previous researches show that the progression of this disease may go largely undetected in the younger population and the onset of presenting symptoms is manifested in "sudden death." This may be due to the lack of presenting symptoms or misdiagnosis The American Heart Association has issued recommendations for athletes to have routine physical exams where IHSS may be detected.Pathophysiology:
IHSS is marked by enlargement and thickening of septal otherwise known as hypertrophy thus taking up the chamber cavity of the heart. This creates obstruction to the blood flow particularly from the left ventricle. Patients that suffer from IHSS usually have a certain degree of valvular insufficiency, and these patients initially experience dynamic outflow obstruction of the valves. This can be seen in the aortic or mitral valves, or both. Approximately two thirds of the patients with IHSS have some degree of mitral valve malformation. This has been displayed as either a primary cause such as the mitral valve being abnormally attached to the papillary muscles becoming thickened or causing a strong mid-cavity obstruction, or due to systolic anterior motion (SAM) of the mitral valve. The severity of SAM can be visualized via echocardiography and is thought to be secondary to the Venturi effect of blood flow through a narrowed opening thereby pulling the mitral valve into the outflow tract and further worsening the obstruction. This condition results in diastolic dysfunction or poor filling and relaxation, systolic dysfunction or end stage dilation and myocardial inchemia or increased demand for oxygen due to increased myocardial mass (Stead, Stead & Kaufman, 2006). The involvement of the aortic valve usually occurs when the hypertrophied intraventricular septum obstructs outflow tract of the aortic valve leading to a blockage and aortic insufficiency
The progression of IHSS has been closely linked to the following factors:
- Dynamic obstruction of left ventricular outflow caused by SAM and obstruction to the septal wall
- Impaired diastolic function
- Decreased coronary perfusion or reserve / ischemia
The obstruction of outward flow from the abnormally hypertrophied intraventricular septal wall can further potentiate the venturi effect of SAM thereby worsening the degree of mitral valve incompetence. The increased wall thickness of the myocardium leads to a much more narrowed chamber space further potentiating the diastolic dysfunction and increasing left ventricular end diastolic pressure. The coronary arteries become compromised primarily from the diastolic dysfunction, and increased myocardial demand. Presenting symptoms usually include angina pectoris, syncope, tachydysrhythmias, fatigue, orthopnea, arterial fibrillation, migration joint pain, edema, and abdominal pain, dyspnea on exertion and congestive heart failure as well as sudden death.Diagnosis:
Diagnosis of IHSS; ECG: PVCs, LVH, septal Q waves, atrial fibrillation, T wave abnormalities and non specific ST segment. Echocandiography is also used which includes small size of LVH, septal hypertrophy, nitral regurgitation using systolic anterior movement of mitral valve leaflets and atrial dilatation. The diagnosis is done by first conducting a heart exam where a loud S4 noise is revealed. There is also a murmur which aggravates with Valsalva's maneuver and also declines with squatting. After carrying out an examination using an electrocardiogram a ventricular hypertrophy is revealed. Delayed left ventricle filling and asymmetrical left ventricular hypertrophy is shown using echocardiogram. Lastly, the Doppler test reveals a dynamic gradient and turbulent flow across the aortic valve coupled with mitral regurgitation.Anesthesia management:
The prime objective of anesthesia management for IHSS patients is to check on the pressure gradient across the obstruction of the left ventricular. This calls for the use of volatile anesthetics to maintain anesthesia because they give moderate depression of myocardial contractility. Agents such as desflurane, isoflurane and sevoflurane are less ideal alternative than halothane because they serve to decrease systematic vascular resistance more than what halothane does (Stoelting & Miller, 2007). Notably, halothane is not widely used because it has a dysrhythmogenic potential and issues regarding halothane hepatitis. In this case volatile aesthetics are combined with opioids. Opioids are not used as the main anesthetic because they are incapable of producing myocardial depression. They also have the potential to reduce systematic vascular resistance. Intra-operative hypotension is countered with alpha-agonist like phenylephrine or intravenous fluids. Beta-agonist activity drugs are not recommended because they increase cardiac contractility. They can also cause heart rate increase. In event of systematic hypertension, a concentration of volatile drugs (sevoflurane, isoflurane) should be increased. Use of vasodilators like nitroglycerin should be done cautiously when the need to lower systematic blood pressure arises. This is because decline in systematic vascular resistance can lead to an increase in obstruction of left ventricular outflow (Stoelting & Miller, 2007).Pre-operative:
During the preoperative period there are several anesthetic considerations which must be made. One of them is pre-medication where agents which cause anxiety like tachycardia should be avoided. Patients who have a history of abusing intravenous drugs have the potential to have bacterial endocarditis which could result to lesions. In this case, antibiotic prophylaxis and preoperative anticoagulations should be used before surgery. Patients with sinus tachycardia should be assessed for hypovolemia, hyperthermia, autonomic dysfunction and thyrotoxicosis. Stabilization in this case will be a good solution to the problem but surgery may be called for if emergent. Patients with a permanent or temporary complete atrioventricular block should be given a preoperative placement of a pacemaker. On the other hand, patients with functioning pacemakers should be taken through a thorough scrutiny to establish the type of pacemaker in place. This is where questions regarding the chamber in place, its sensing pattern and the rhythm. It's also imperative to pre-plan the possible course of action if the pacemaker in place malfunctions due to variations in radio frequency. Preoperative procedures should also be carried out on the patients' respiratory system to identify the consequences and characteristics of the diseases. Just before surgery aggressive arrhythmia should be avoided including all meds related to arrhythmia. Cardioversion should also be avoided too. It's also important to maintain enough intravascular volume and preload. Beta adrenergic blockers and ca channel blockers which decrease contractility and prevent increases in Subaortic pressure gradients should be administered.Intra-operative:
During surgery, a high level of monitoring should be ensured especially on HR and contractility to avoid reflex or direct increase. Hypotension should also be avoided and CVP should be elevated to high normal level. This should also be the case with other deliverables like CVP, PAC, PCWP and CPP. Other areas of basic monitoring are oxygenation where pulse rate, skin color and inspired oxygen concentration is monitored. The other area of monitoring is ventilation, circulation and temperature. Circulation monitors blood pressure, heart rate, peripheral perfusion and electrocardiogram. There is also the monitoring of the body system like respiratory system, cardiovascular system, renal function, central nervous system, metabolic system, coagulation and circulating volume (Lawrence, Bell & Dayton, 2007). This is where crucial decisions regarding the type of anesthetic to use are made because they predict the intra-operative process. The recommended ones should have no difference in the rates of infarcation, no hypotension and tachycardia. The other important predictor of this stage is the site of surgery. This is because different parts of the body are affected different depending on the extremes of the procedure to be conducted. For example the upper abdominal and thoracic are exposed to a higher risk if extreme procedures are carried. There is also the duration taken by anesthetic to clear the effect where aesthetics taking more that three hours posing a risk of mortality and morbidity. The nature of the surgery also determines the outcome of this stage with emergency surgery posing greater risks. This process may involve several activities depending on the actual problem. For example a cardiopulmonary bypass may be made or ventriculomyotomy. The intra-operative procedure is provided to ensure that everything runs as expected.Post-operative:
Immediately after the surgery, analgesia should be maintained. There should also be a balance of supply and demand as well as an ample supply of supplemental oxygen. A pain therapy should also be conducted to keep away extreme sympathetic stimulation. Success in controlling post-operative pain improves the outcome of the patient by facilitating therapy, preventing complication as well as hastening recovery and discharge (Lawrence, Bell & Dayton, 2007). Surveillance for ischemia is also advocated for after surgery. ECG abnormalities should be assessed by comparing preoperative ECG with postoperative ECG (Twersky & Philip, 2008). In managing ischemia after the operation agents such as beta blockers, aspirin, nitrates including cardiology consultation. , There should also be continuous monitoring to establish the patients progress into the postoperative period. Early transfusion may be carried out later.Medical management:
The prime objectives of treating IHSS are to make sure that the ventricles are relaxed as wella s to relieve the obstruction of the outflow tract. Drugs are first used in managing this condition medically while surgery may be employed as the last resort when everything else has failed to deliver the required results. However, surgery is rarely used. The most commonly used drugs are metoprolol or propranolol which acts as beta-adrexnergic blocking agents. They serve to slow down the heart rate and encourage filling of the ventricle. This is achieved by relaxing the obstructing muscle thus reducing syncope, angina and arrhythmias. The other drug which is used is calcium channel blockers which acts to reduce high diastolic pressures. They also decrease the seriousness of the outflow tract gradient and increasing exercise tolerance too. Left ventricular hypercontractibility and gradient of the outflow are reduced by using disopyramide. During episodes atrial fibrillation, heparin is administered. These episodes are medical emergency which requires cardioversion due to the embedded risk of systemic embolism and that is why heparin should be administered till fibrillation reduces. In extreme cases of heart failure, amiodarone is administered through its application should be avoided in situations where atri-oventricular block exists. Amiodarone is also very effective in enhancing left ventricular pressure gradients and reduction of supraventricular and ventricular arrhythmias.
However, there are other drugs which should be avoided in the course of managing IHSS medically. These are vasodilators like diuretic and nitroglycerin. This is because they reduce return of the venous by allowing blood pooling in the periphery. This has the adverse effect of decreasing volume of the ventricular and size of the chamber causing further obstruction. The other drugs which should be avoided are the inotropic and sympathetic stimulators because they increase4 cardiac contractibility. Enlargement of the septum asymmetrically has the potential effect of obstructing left ventricular outflow thus causing decreased cardiac output. Basically, any medical initiative which increases contractibility is bound to increase obstruction (LWW medical Books Collection, 2008)
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- LWW medical book collection. (2008). Pathophysiology Made Incredibly Easy! Lippincott Williams & Wilkins.
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- Twersky, R. S. & Philip, B. K. (2008). Handbook of Ambulatory Anesthesia. New York: Springer