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Treating obstruction in hypertrophic cardiomyopathy

Dr Antonis Pantazis, consultant cardiologist at the Heart Hospital in London, discusses lifestyle, medication, devices and surgery

Hypertrophic cardiomyopathy is a disease of the heart muscle that is often complicated by obstruction in the outflow area of the main pumping chamber of the heart, the left ventricle. This generates a pressure difference between the heart and the aorta, the main artery that takes the blood to the circulatory system.

Mechanism and symptoms of obstruction

Obstruction occurs in one third of the total hypertrophic cardiomyopathy (HCM) population at rest and in an additional third due to factors such as exercise.

What causes it is the abnormal motion of the mitral valve towards the thickened wall of the heart in the area of the outflow.

Patients with obstruction often experience symptoms on exertion and are limited in their physical activities. The nature of the obstruction is changeable and typically affected by the strength of the contraction of the heart muscle.
The more vigorous the contraction, the more significant the obstruction. Therefore, circumstances and medication that affect the pumping function of the heart muscle are having an impact on the obstruction.

Furthermore, anything that reduces the size of the inner heart by reducing the circulating volume of blood or by increasing the capacity of the veins and arteries can increase the pressure difference in the outflow area. Examples of these conditions can be bleeding, dehydration, big meals, alcohol intake, hot weather or antihypertensive medication. 

Symptoms related to obstruction can be breathlessness, chest tightness or pain, fainting or near fainting.

Management of obstruction

Adaptation to the limitations                                                                                                             

Patients often learn to identify and avoid the circumstances that increase the pressure difference between the heart and the aorta. This adaption is occasionally subconscious and patients may not even be fully aware of the degree of limitations they have in their physical activities. 

Medication

Different types of medication are used to manage the obstruction in the exit flow of the heart. The medication group that is usually tried first, if there is not any cardiac or extracardiac contraindication, are betablockers such as bisoprolol, atenolol or metoprolol. Rarely in combination with the betablockers, but often as an alternative, drugs belonging to the calcium antagonists group, such as verapamil and diltiazem, are used.

Finally, disopyamide is another drug that can be used in combination with either a betablocker or a calcium antagonist. The response to drug treatment varies from a significant improvement to no benefit at all. It is interesting to note that all these medications reduce the strength of the heart’s contraction and slow down the heart rate.

Although the medication does not really suppress the heart function to such an extent that would cause dysfunction, a common side-effect can be fatigue and tiredness. These symptoms unfortunately overlap with limitations caused by the condition itself and it is often challenging to achieve the balance between side-effects and benefit. Each of the pharmaceutical agents that we use also has side-effects.

Interventions

When lifestyle changes and medication are not enough, the patient with HCM and outflow tract obstruction may be considered for an intervention. A number of cardiac and other factors are examined before the decision is made.

The cardiac factors include the precise heart anatomy, the extent of the hypertrophy, the condition of the valves and coronary arteries, and the heart rhythm. Other factors include the age of the patient, their weight and the coexisting condition of other organs, for example the lungs, kidneys and carotid arteries. This information affects the decision on what is the best treatment option and the risks associated with each option. So they seriously influence the decision made.

Pacemaker implantation

Back in the 1990s it was suggested that a pacemaker that would pace the heart at the right ventricular apex (the bottom of the chamber that is located next to the left ventricle) could be beneficial. It was thought that this would slightly change the way the heart contracts to relieve the left ventricular obstruction.  Initial reports were very encouraging but subsequent clinical studies demonstrated that the method was largely ineffective.

Nevertheless, some patients will still benefit from pacemaker implantation. However, it is very challenging to predict who would benefit from this method. Therefore, the implantation of a pacemaker mainly remains an option for those patients with obstruction who require a pacemaker for other reasons as well, such as those who develop bradycardia (slow heart rate), either spontaneously or as a result of administration of necessary medication. It may also be an option for those patients in whom all other interventions are contraindicated.

Alcohol septal ablation

                     Alcohol septal ablation


For those patients with a significant degree of outflow obstruction who have symptoms limiting their daily activities, further interventions are usually considered.
An attractive therapeutic option is a non-surgical reduction of the thickness of the ventricular muscle in the area of the outflow tract. What is practically done in this case is that the tip of a catheter is wedged in a small artery that supplies the thick muscle with blood. Then, the area of supply is carefully checked with imaging and an injection of a contrast agent.

If appropriate, a small controlled heart attack is caused in the upper interventricular septum by injecting a small amount of ethanol through the catheter. This results in scarring and shrinking of the wall thickness and is anticipated to reduce or even eliminate the intra-ventricular obstruction. Nevertheless, the improvement may not manifest itself immediately after the procedure.

The risk of complications is similar to the risks of surgery (overall mortality is about one per cent) but advantages are a shorter hospital stay and more rapid recovery. The medium term effect of the procedure on the pressure gradient and the improvement of exercise capacity is good but the long term effects are unknown and therefore the option is generally avoided in very young patients.

                                                                                                                                                                                                                                     

Surgical myectomy

                          Surgical myectomy

The surgical approach is to perform a myectomy. This is a technically demanding operation that requires surgical expertise. The surgeon reaches the inner surface of the thick wall of the heart through the main valve that allows the blood out (aortic valve) and removes some of the thickened muscle.

The amount of muscle that is taken out is approximately two to three per cent of the total weight of the heart and is usually enough to relieve the blockage. Because of the complexity of the anatomy in the area of obstruction, the procedure is guided by intra-operative echocardiogram but obviously it largely relies on the surgeon’s skill to take the muscle out from the right place.

Occasionally, the resection of the muscle is not sufficient and then the team may decide to proceed with a repair or replacement of the mitral valve which is responsible for the outflow tract obstruction. This is more likely to be the case when the valve is intrinsically abnormal.

The mortality rate is similar to a septal ablation. Another complication can be a complete electrical block which requires implantation of a permanent pacemaker. This is reported in around five per cent of cases. Rarely, an accidentally created small hole in the area of the resection can complicate the operation.

The resolution of obstructive symptoms is usually fast but the recovery from a big operation may take a while. Although usually performed for the relief of symptoms, there is some data suggesting that this operation can improve survival as well.

                                                                                                                                                                                                                                

Conclusion

The left ventricular outflow obstruction which often complicates hypertrophic cardiomyopathy can be managed with a variety of approaches. In the majority of patients a significant improvement in symptoms should be possible.









The Cardiomyopathy Association's Registered Charity Number is 803262.
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