Non-coronary percutaneous intervention
Balloon mitral valvuloplasty
Acquired mitral stenosis is a consequence of rheumatic fever and is commonest in developing countries. Commissural fusion, thickening, and calcification of the mitral valve leaflets typically occur, as well as thickening and shortening of the chordae tendinae. The mitral valve stenosis leads to left atrial enlargement, which predisposes patients to atrial fibrillation and the formation of left atrial thrombus.In the 1980s percutaneous balloon valvuloplasty techniques were developed that could open the fused mitral commissures in a similar fashion to surgical commissurotomy. The resulting fall in pressure gradient and increase in mitral valve area led to symptomatic improvement. Today, this procedure is most often performed with the hourglass shaped Inoue balloon. This is introduced into the right atrium from the femoral vein, passed across the atrial septum by way of a septal puncture, and then positioned across the stenosed mitral valve before inflation.
Stenotic mitral valve showing distorted, fused, and calcified valve leaflets.septal ablation
(AMVL=anterior mitral valve leaflet, PMVL=posterior mitral valve leaflet,
LC=lateral commissure, MC=medial commissure)septal ablation
Fluoroscopic
image of the inflated Inoue balloon across the valve.septal ablation
Patient selection
In general, patients with moderate or severe mitral stenosis (valve area < 1.5 cm2) with symptomatic disease despite optimal medical treatment can be considered for this procedure. Further patient selection relies heavily on transthoracic and transoesophageal echocardiographic findings, which provide structural information about the mitral valve and subvalvar apparatus.A scoring system for predicting outcomes is commonly used to screen potential candidates. Four characteristics (valve mobility, leaflet thickening, subvalvar thickening, and calcification) are each graded 1 to 4. Patients with a score of <8 are more likely to have to have a good result than those with scores of > 8. Thus, patients with pliable, non-calcified valves and minimal fusion of the subvalvar apparatus achieve the best immediate and long term results.
Relative contraindications are the presence of pre-existing significant mitral regurgitation and left atrial thrombus. Successful balloon valvuloplasty increases valve area to > 1.5 cm2 without a substantial increase in mitral regurgitation, resulting in significant symptomatic improvement.
Complications—The major procedural complications are death (1%), haemopericardium (usually during transseptal catheterisation) (1%), cerebrovascular embolisation (1%), severe mitral regurgitation (due to a torn valve cusp) (2%), and atrial septal defect (although this closes or decreases in size in most patients) (10%). Immediate and long term results are similar to those with surgical valvotomy, and balloon valvuloplasty can be repeated if commissural restenosis (a gradual process with an incidence of 30-40% at 6-8 years) occurs.
In patients with suitable valvar anatomy, balloon valvuloplasty has become the treatment of choice for mitral stenosis, delaying the need for surgical intervention. It may also be of particular use in those patients who are at high risk of surgical intervention (because of pregnancy, age, or coexisting pulmonary or renal disease). In contrast, balloon valvuloplasty for adult aortic stenosis is associated with high complication rates and poor outcomes and is only rarely performed.
Ethanol septal ablation
Hypertrophic cardiomyopathyHypertrophic cardiomyopathy is a disease of the myocytes caused by mutations in any one of 10 genes encoding various components of the sarcomeres. It is the commonest genetic cardiovascular disease, being inherited as an autosomal dominant trait and affecting about 1 in 500 of the population. It has highly variable clinical and pathological presentations. It is usually diagnosed by echocardiography and is characterised by the presence of unexplained hypertrophy in a non-dilated left ventricle. In a quarter of cases septal enlargement may result in substantial obstruction of the left ventricular outflow tract. This is compounded by Venturi suction movement of the anterior mitral valve leaflet during ventricular systole, bringing it into contact with the hypertrophied septum. The systolic anterior motion of the anterior mitral valve leaflet also causes mitral regurgitation.
Postmortem appearance of a heart with hypertrophic cardiomyopathy showing massive ventricular and septal hypertrophy causing obstruction of the left
ventricular outflow tract(LVOT).septal ablation. This is compounded by the anterior mitral valve leaflet(AMVL), which presses
against the ventricular septum (VS).septal ablation. Note the coincidental right atrial(RAE) and right ventricular(RVE) pacing electrodes.septal ablation
Treatment
Although hypertrophic cardiomyopathy is often asymptomatic, common symptoms are dyspnoea, angina, and exertional syncope, which may be related to the gradient in the left ventricular outflow tract. The aim of treatment of symptomatic patients is to improve functional disability, reduce the extent of obstruction of the left ventricular outflow tract, and improve diastolic filling. Treatments include negatively inotropic drugs such as blockers, verapamil, and disopyramide. However, 10% of symptomatic patients fail to respond to drugs, and surgery— ventricular myectomy (which usually involves removal of a small amount of septal muscle) or ethanol septal ablation—can be considered.
The objective of ethanol septal ablation is to induce a localised septal myocardial infarction at the site of obstruction of the left ventricular outflow tract. The procedure involves threading a small balloon catheter into the septal artery supplying the culprit area of septum. Echocardiography with injection of an echocontrast agent down the septal artery allows the appropriate septal artery to be identified and reduces the number of unnecessary ethanol injections.
Once the appropriate artery is identified, the catheter balloon is inflated to completely occlude the vessel, and a small amount of dehydrated ethanol is injected through the central lumen of the catheter into the distal septal artery. This causes immediate vessel occlusion and localised myocardial infarction. The infarct reduces septal motion and thickness, enlarges the left ventricular outflow tract, and may decrease mitral valve systolic anterior motion, with consequent reduction in the gradient of the left ventricular outflow tract. Over the next few months the infarcted septum undergoes fibrosis and shrinkage, which may result in further symptomatic improvement.
The procedure is performed under local anaesthesia with sedation as required. Patients inevitably experience chest discomfort during ethanol injection, and treatment with intravenous opiate analgesics is essential. Patients are usually discharged after four or five days.
Complications
Heart block is a frequent acute complication, so a temporary pacing electrode is inserted via the femoral vein beforehand and is usually left in situ for 24 hours after the procedure, during which time the patient is monitored.
The main procedural complications are persistent heart block requiring a permanent pacemaker (10%), coronary artery dissection and infarction requiring immediate coronary artery bypass grafting (2%), and death (1-2%). The procedural mortality and morbidity is similar to that for surgical myectomy, as is the reduction in left ventricular outflow tract gradient. Surgery and ethanol septal ablation have not as yet been directly compared in randomised studies.
Characteristics of hypertrophic cardiomyopathy
Anatomical—Ventricular hypertrophy of unknown cause, usually with disproportionate involvement of the interventricular septum
Physiological—Well preserved systolic ventricular function, impaired diastolic relaxation
Pathological—Extensive disarray and disorganisation of cardiac myocytes and increased interstitial collagen
Echocardiogram showing anterior mitral valve
leaflet (AMVL) and septal contact (***) during
ventricular systole.septal ablation. Note marked left ventricular (LV)
free wall and ventricular septal (VS) hypertrophy.septal ablation
Injection of an echocontrast agent down the septal
artery results in an area of septal echo-brightness
(dotted line). (LA=left atrium, AoV=aortic valve)septal ablation
Angiograms showing ethanol septal ablation. The first septal artery (S1,left)
is occluded with a balloon catheter (center) before ethanol injection.septal ablation, This results in permanent septal artery occlusion (right)
and a localised septal myocardial infarction. (LAD=left anterior descending artery, TPW=temporary pacemaker wire)septal ablation
Micrograph of hypertrophied myocytes in haphazard
alignments characteristic of hypertrophic cardiomyopathy. Interstitial collagen is also increased
Septal defect closure
Atrial septal defectsAtrial septal defects are congenital abnormalities characterised by a structural deficiency of the atrial septum and account for about 10% of all congenital cardiac disease. The commonest atrial septal defects affect the ostium secundum (in the fossa ovalis), and most are suitable for transcatheter closure. Although atrial septal defects may be closed in childhood, they are the commonest form of congenital heart disease to become apparent in adulthood.
Diagnosis is usually confirmed by echocardiography, allowing visualisation of the anatomy of the defect and Doppler estimation of the shunt size. The physiological importance of the defect depends on the duration and size of the shunt, as well as the response of the pulmonary vascular bed. Patients with significant shunts (defined as a ratio of pulmonary blood flow to systemic blood flow > 1.5) should be considered for closure when the diagnosis is made in later life because the defect reduces survival in adults who develop progressive pulmonary hypertension. They may also develop atrial tachyarrhythmias, which commonly precipitate heart failure.
Patients within certain parameters can be selected for transcatheter closure with a septal occluder. In those who are unsuitable for the procedure, surgical closure may be considered.
Indications and contraindications for percutaneous closure of atrial septal defects
IndicationsClinical
Anatomical
Contraindications
Deployment sequence of the Amplatzer septal occluder for closing an atrial septal defect(septal ablation)
A patent foramen ovale is a persistent flap-like opening between the atrial septum primum and secundum which occurs in roughly 25% of adults.With microbubbles injected into a peripheral vein during echocardiography, a patent foramen ovale can be demonstrated by the patient performing and releasing a prolonged Valsalva manoeuvre. Visualisation of microbubbles crossing into the left atrium reveals a right-to-left shunt mediated by transient reversal of the interatrial pressure gradient.
Although a patent foramen ovale (or an atrial septal aneurysm) has no clinical importance in otherwise healthy adults, it may cause paradoxical embolism in patients with cryptogenic transient ischaemic attack or stroke (up to half of whom have a patent foramen ovale), decompression illness in divers, and right-to-left shunting in patients with right ventricular infarction or severe pulmonary hypertension. Patients with patent foramen ovale and paradoxical embolism have an approximate 3.5% yearly risk of recurrent cerebrovascular events.
Secondary preventive strategies are drug treatment (aspirin, clopidogrel, or warfarin), surgery, or percutaneous closure using a dedicated occluding device. A lack of randomised clinical trials directly comparing these options means optimal treatment remains uncertain. However, percutaneous closure offers a less invasive alternative to traditional surgery and allows patients to avoid potential side effects associated with anticoagulants and interactions with other drugs. In addition, divers taking anticoagulants may experience haemorrhage in the ear, sinus, or lung from barotrauma.
Amplatzer occluder devices for patent foramen ovale (left)
and muscular ventricular septal defects (right)septal ablation
Untreated congenital ventricular septal defects that require intervention are rare in adults. Recently, there has been interest in percutaneous device closure of ventricular septal defects acquired as a complication of acute myocardial infarction. However, more experience is necessary to assess the role of this procedure as a primary closure technique or as a bridge to subsequent surgery.
The picture of a stenotic mitral valve and micrograph of myocytes showing hypertrophic cardiomyopathy were provided by C Littman, consultant histopathologist at the Health Sciences Centre, Winnipeg, Manitoba, Canada. The postmortem picture of a heart with hypertrophic cardiomyopathy was provided by T Balachandra, chief medical examiner for the Province of Manitoba,Winnipeg. The pictures of Amplatzer occluder devices were provided by AGA Medical Corporation, Minnesota, USA.
Septal ablation
Septal ablation involves injecting an alcohol solution into the heart, purposely causing a strategically localized "heart attack" to treat the symptoms of hypertrophic obstructive cardiomyopathy (HOCM) by destroying a small area of the muscle. As a new procedure, developed over the past decade, septal ablation is considered experimental by the American Heart Association. Although this procedure is performed using heart catheterization as opposed to open-heart surgery, it is no safer than a myectomy. It's too soon to estimate the long-term benefits and safety issues of septal ablation therapy.Septal ablation is a heart catheterization procedure that usually lasts between one and two hours. Patients are awake and able to talk throughout the procedure, although they may be given sedatives to help them relax. Catheters are used to implant a temporary pacemaker, as a safety measure, and to perform an angiography to visualize the blood vessels and small arteries of the heart that carry blood to the overgrown muscle that is causing the obstruction. Once the blood vessels of the overgrown area have been identified, alcohol is injected into the catheter to destroy the tissue in the overgrown area of the heart muscle as shown in Figure 6. Over time, the tissue scars and shrinks, decreasing the obstruction to blood flow and improving the symptoms of HOCM.
While this procedure is relatively new, information from research studies suggests that septal ablation can, in appropriately chosen patients, relieve symptoms to a similar degree as septal myectomy. The success of the treatment largely depends on the ability of the cardiologist to correctly identify and isolate the area of the heart causing the obstruction. Approximately 5 percent to 10 percent of the patients undergoing a septal ablation will need a pacemaker due to damage of the conduction system of the heart resulting from the procedure. In addition, the procedure is too new for long-term outcomes to be understood. There may be unknown safety issues, such as long-term risks of abnormal and potentially lethal heart rhythms associated with scarring of the heart muscle.Although many centers are equipped with heart catheterization facilities, it can be very difficult to control the extent of the "heart attack" within the heart muscle. Septal ablation should be performed only by an experienced cardiologist specializing in this procedure.
Not all people with HOCM are candidates for septal ablation. The unique anatomy of each individual heart must be considered; the anatomies of some hearts are not conducive to septal ablation treatment. For some people, there may be other health concerns to consider that preclude the use of this treatment. On the other hand, septal ablation is a good alternative for people who are not candidates for surgery or do not want to undergo heart surgery. BACK HOME NEXT