the valve being connected to the right ventricle. ventricular septal defect (vsd) a hole between the two bottom chambers (ventricles) of the heart. the defect is centered around the most superior aspect of the ventricular septum (the outlet septum), and in the majority of cases is single and large. in some cases, thickening of the septum (septal hypertrophy) can narrow the margins of the defect. right ventricular hypertrophy the right ventricle is more muscular than normal, causing a characteristic boot-shaped (coeur-en-sabot) appearance as seen by chest x-ray. due to the misarrangement of the external ventricular septum, the right ventricular wall increases in size to deal with the increased obstruction to the right outflow tract. this feature is now generally agreed to be a secondary anomaly, as the level of hypertrophy tends to increase with age. fallot's tetralogy specimen, from the uct pathology learning centre there is anatomic variation between the hearts of individuals with tetralogy of fallot. primarily, the degree of right ventricular outflow tract obstruction varies between patients and generally determines clinical symptoms and disease progression. presumably, this arises from an unequal growth of the aorticopulmonary septum (aka pulmonary outflow septum).: 199 the aorta is too large, thus "overriding," and this "steals" from the pulmonary artery, which is therefore stenosed. this then prevents ventricular wall closure, therefore vsd, and this increases the pressures on the right side, and so the r ventricle becomes bigger to handle the work.: 199 additional anomalies in addition, tetralogy of fallot may present with other anatomical anomalies, including:: 66–8 stenosis of the left pulmonary artery, in 40% a bicuspid pulmonary valve, in 60% right-sided aortic arch, in 25% coronary artery anomalies, in 10% a patent foramen ovale or atrial septal defect, in which case the syndrome is sometimes called a pentalogy of fallot an atrioventricular septal defect partially or totally anomalous pulmonary venous return tetralogy of fallot with pulmonary atresia (pseudotruncus arteriosus) is a severe variant in which there is complete obstruction (atresia) of the right ventricular outflow tract, causing an absence of the pulmonary trunk during embryonic development.: 67–8 in these individuals, blood shunts completely from the right ventricle to the left where it is pumped only through the aorta. the lungs are perfused via extensive collaterals from the systemic arteries, and sometimes also via the ductus arteriosus.: 67–8 diagnosis a chest x-ray of a child with tetralogy of fallot there are three different useful diagnostic tests used for the diagnosis of tetralogy of fallot. these include a chest radiograph, electrocardiogram, and echocardiogram. the echocardiography determines the final diagnosis and typically offers enough information for surgical treatment planning. about half of all patients are now diagnosed before they are born. differential diagnosis is when physicians diagnose between two or more conditions for a person's symptoms and this can include primary pulmonary causes of cyanosis, cyanotic heart lesions, pulmonary stenosis and transposed arterial trunks. chest radiograph before more sophisticated techniques became available, chest x-ray was the definitive method of diagnosis. the abnormal "coeur-en-sabot" (boot-like) appearance of a heart with tetralogy of fallot is classically visible via chest x-ray, although most infants with tetralogy may not show this finding. the boot like shape is due to the right ventricular hypertrophy present in tof. lung fields are often dark (absence of interstitial lung markings) due to decreased pulmonary blood flow.: 171–72 electrocardiogram an electrocardiogram (ecg) is one of the most basic procedures for assessing the heart. tiny electrodes are applied to specific areas on the body, near the chest, arm, and neck. lead cables connect the electrodes to an ecg machine. the heart's electrical activity is then measured. natural electrical impulses help maintain blood flowing properly by coordinating contractions in different areas of the heart. these impulses are recorded by an ecg, which shows how fast, the rhythm, intensity and timing of the electrical impulses as they travel through the heart. electrocardiography shows right ventricular hypertrophy (rvh), along with right axis deviation. rvh is noted on ekg as tall r-waves in lead v1 and deep s-waves in lead v5-v6. echocardiogram congenital heart defects are now diagnosed with echocardiography, which is quick, involves no radiation, is very specific, and can be done prenatally. echocardiography establishes the presence of tof by demonstrating a vsd, rvh, and aortic override. many patients are diagnosed prenatally. color doppler (type of echocardiography) measures the degree of pulmonary stenosis. additionally, close monitoring of the ductus arteriosus is done in the neonatal period to ensure that there is adequate blood flow through the pulmonary valve.: 171–72 in certain cases, coronary artery anatomy cannot be clearly viewed using echocardiogram. in this case, cardiac catheterization can be done.: 37, 201 genetics from a genetics perspective, it is important to screen for digeorge in all babies with tof.: 37, 201 treatment tet spells tet spells are defined as cyanotic spells occurring due to the obstruction right ventricular outflow. tet spells can be triggered by various factors such as crying, progressive tachypnea, and deep breathing, with symptoms including but not limited to blue skin, nails and lips, profound crying and difficulty breathing. tet spells may be treated with beta-blockers such as propranolol, but acute episodes require rapid intervention with morphine or intranasal fentanyl to reduce ventilatory drive, a vasopressor such as phenylephrine, or norepinephrine to increase systemic vascular resistance, and iv fluids for volume expansion.: 18, 201 oxygen (100%) may be effective in treating spells because it is a potent pulmonary vasodilator and systemic vasoconstrictor. this allows more blood flow to the lungs by decreasing shunting of deoxygenated blood from the right to left ventricle through the vsd. there are also simple procedures such as squatting and the knee chest position which increase systemic vascular resistance and decrease right-to-left shunting of deoxygenated blood into the systemic circulation.: 18, 201 if the spells are refractory to the above treatments, people are usually intubated and sedated. the treatment of last resort for tet spells is extracorporeal membrane oxygenation (ecmo) along with consideration of blalock taussig shunt (bt shunt).: 18, 201 total surgical repair total surgical repair of tof is a curative surgery. different techniques can be used in performing tof repair. however, a transatrial, transpulmonary artery approach is used for most cases.: 153 the repair consists of two main steps: closure of the vsd with a patch and reconstruction of the right ventricular outflow tract. this open-heart surgery is designed to relieve the right ventricular outflow tract stenosis by careful resection of muscle and to repair the vsd.: 154 the right ventricle outflow tract can be reconstructed using mainly 2 procedures: a transannular patch (tap) or a pulmonary valve-sparing procedure (pvs). the decision on the type of the procedure depends on individual anatomy (especially the size of the pulmonary valve). pvs showed better overall survival, event-free survival and less pulmonary regurgitation at 10, 20 and 30 years after the operation. pvs can be performed with or without ventriculotomy. a study found similar overall and event-free survival and pulmonary regurgitation rate between patients who underwent pvs with ventriculotomy and the ones who did not. additional reparative or reconstructive surgery may be done on patients as required by their particular cardiac anatomy.: 153 timing of surgery in asymptomatic patients is usually between the ages of two months to one year.: 201–2 however, in symptomatic patients showing worsening blood oxygen levels, severe tet-spells (cyanotic spells), or dependence on prostaglandins from early neonatal period (to keep the ductus arteriosus open) need to be planned fairly urgently: 201–2 potential surgical repair complications include residual ventricular septal defect, residual outflow tract obstruction, complete atrioventricular block, arrhythmias, aneurysm of right ventricular outflow patch, and pulmonary valve insufficiency.: 59 long-term complications most commonly include pulmonary valve regurgitation, and arrhythmias. total repair of tetralogy of fallot initially carried a high mortality risk, but this risk has gone down steadily over the years. surgery is now often carried out in infants one year of age or younger with less than 5% perioperative mortality.: 205 post surgery, most patients enjoy an active life free of symptoms.: 205 currently, long-term survival is close to 90%.: 167 today the adult tof population continues to grow and is one of the most common congenital heart defects seen in adult outpatient clinics.: 100–101 palliative surgery initially surgery involved forming a side to end anastomosis between the subclavian artery and the pulmonary artery -i.e. a systemic to pulmonary arterial shunt.: 57 this redirected a large portion of the partially oxygenated blood leaving the heart for the body into the lungs, increasing flow through the pulmonary circuit, and relieving symptoms. the first blalock-thomas-taussig shunt surgery was performed on 15-month-old eileen saxon on november 29, 1944 with dramatic results. the potts shunt and the waterston-cooley shunt are other shunt procedures which were developed for the same purpose. these are no longer used. currently, palliative surgery is not normally performed on infants with tof except for extreme cases.: 173 for example, in symptomatic infants, a two-stage repair (initial systemic to arterial shunt placement followed by total surgical repair) may be done. potential complications include inadequate pulmonary blood flow, pulmonary artery distortion, inadequate growth of the pulmonary arteries, and acquired pulmonary atresia.: 59 approaches to surgical repair after years of tetralogy of fallot surgical repair expertise, the attention shifted to the emerging evidence that long-term pulmonary insufficiency is detrimental to right ventricular function and clinical prognosis. as a result, the hunt for surgical procedures to relieve right ventricular outflow tract obstruction while minimizing pulmonary regurgitation has intensified. a constrained right ventricular outflow tract reconstruction with a dacron patch matched to a nominal pulmonary annulus expansion or an annulus-sparing approach yielded primary complete repair outcomes in 94 tof infants. the pulmonary annulus size was larger in babies treated with the latter technique, as predicted. after an average follow-up of around eight years, the first group had a higher than moderate pr, yet there was no significant difference in independence from severe pr after ten years. furthermore, there was no significant difference in right ventricular dilation between the two techniques. finally, they found that reconstructing the pulmonary annulus in tof with only a tiny transannular incision and a stiff dacron patch to inhibit pulmonary annulus extension throughout the normal growing phase produces the same long-term benefits as preserving the full pulmonary annulus integrity. complications short-term residual ventricular septal defects and persistent right ventricular outflow blockage are common problems in the immediate postoperative period. arrhythmias such as ventricular tachycardia, atrial fibrillation/flutter, and intra-atrial re-entrant tachycardia can occur after tetralogy repair. with broad complex tachycardia, the ecg will likely show a right bundle branch block or left bundle branch block patterns. patients who have had their hearts repaired may experience sudden cardiac death. risk factors for abnormal heart rhythms include: age (at repair) male gender transient complete heart block beyond post operative day three qrs duration greater than 180 milliseconds long-term adult patients with congenital cardiac disease are on the rise at a rate of about 5% per year, outpacing the pediatric population. right ventricular volume overload form pulmonary insufficiency, right ventricular aneurysm from outflow patch or ventriculotomy, distal pulmonary artery obstruction, ventricular hypertrophy, chamber enlargement, biventricular dysfunction, and aortic root dilation and insufficient are all long-term complications seen in these patients. arrhythmia, heart failure, and complications from reoperations are the three primary causes of death in individuals with corrected tetralogy of fallot. qrs duration greater than 180 milliseconds, older age at repair (greater than three years), significant pulmonary valve or tricuspid valve regurgitation, history of syncope, multifocal premature ventricular contractions, and ventricular tachycardia are some of the factors associated with sudden death after 30 years of procedure. pulmonary insufficiency is the most common reason for reoperation, and pulmonary valve replacement criteria have traditionally been based on the severity of the regurgitant fraction on a magnetic resonance or ct scan. right and left ventricular end-systolic and end-diastolic volume indices, ejection fractions, and the existence of aneurysm generating obstructive outflow are all parameters seen in this research. exercise intolerance, heart failure signs and symptoms, syncope, and prolonged ventricular tachycardia are all possible symptoms. a transcatheter pulmonary valve method can also be used to replace a pulmonary valve. pregnancy in comparison to the general obstetric population, women who had their tetralogy of fallot repaired completely have similar outcomes. the degree of pulmonary regurgitation with