Left ventricular noncompaction cardiomyopathy is a heart muscle condition in which the muscular wall of the main pumping chamber of the heart (the left ventricle) appears to be spongy and “non-compacted”, consisting of a meshwork of numerous muscle bands called trabeculations (see picture left).
This type of cardiomyopathy has not been fully understood so far and remains unclassified by the World Health Organisation, although it is thought to have some individual features. Its cause, development, clinical course and treatment are fields of ongoing research.
The development of the heart
The foetal heart muscle has a non-compacted appearance between the 4th and 18th week of development and this is important for the nutrition of its cells. The spongy-like heart muscle is supplied predominately by diffusion of blood in the heart that flows into the spaces between the muscle bands. Later and simultaneously with the development of the coronary arteries, which will eventually take over carrying blood to the heart muscle, development of the muscle bands appears to go backwards.
The thickness of the compacted wall and the mass of the heart muscle is then increasing and hence the pumping function is increasing too. The final appearance is that of a compacted muscular wall of the heart with minor muscle bands close to its inner surface. Non-compaction cardiomyopathy is thought to result from a halt in this development.
Some limited data suggests that similar cardiac features can be acquired but these observations are of dubious clinical value. In some cases non-compaction can be associated with other congenital cardiac malformations. Experimental studies have shown that the non-compacted appearance of the heart muscle, at least at its extreme, may cause problems with the heart muscle function with impaired pumping strength, and also thin and dilated muscle walls.
The initial clinical observations were made on people who had severe symptoms and it was therefore presumed that this unusual structure of the heart was closely associated with heart failure. More recent studies, though, have demonstrated wider differences in severity and outcome in patients with this disorder.
Prevalence and diagnosis
The number of people with this condition is thought to be very low and it has been found in one in 2,000 echocardiographic studies. The diagnosis is essentially based on purely structural features. The best way to evaluate and diagnose this condition, as accepted by most of the researchers and clinicians, is by quantifying the size and extent of the muscle bands and comparing them against the thickness of the compacted heart muscle.
The ECG may reveal abnormalities but these are usually non-specific, whereas imaging of the heart, such as echocardiography and cardiac MRI, are the most commonly used diagnostic methods. The quantification and diagnosis of the disorder may be neither easy nor objective in many cases and has recently been a topic of significant debate. The diagnosis is further complicated by the fact that overlap of the features of this condition with other heart muscle disorders has been reported. Apparently, the difficulties in the diagnosis may account for the difference in the prevalence reported by various studies.
The currently increased awareness of the condition has recently led to frequent reports in the medical literature of people having the features of noncompaction but the clinical significance of these has to be evaluated with caution.
The symptoms caused by this condition are not specific and are mainly determined by how much the heart function is affected. Individuals who have the described structural features but normal performance of the heart may be entirely free of symptoms. And recent studies and reports have demonstrated a more mild outcome and clinical course of this condition than shown in the initial observations. The whole spectrum of the outcome of this condition, therefore, is still not fully defined.
Presuming that a halt in cardiac development is the cause of this condition, these features should be present in the heart from birth. It is not entirely clear how, when and to what degree the heart function is becoming affected. As soon as the pumping performance of the heart is reduced, symptoms typically related to heart insufficiency may appear. These are usually:
This condition is also thought to be associated with increased risk of blood clots in the meshwork of the prominent heart muscle bands. This is explained by the fact that the blood flow in this region of the heart is relatively slow. Most recent studies have shown that the risk of clot formation has previously been overestimated and is mainly associated with the pumping function of the heart.
Another risk possibly associated with this condition is that of a fast cardiac rhythm which may result in a drop in blood pressure, loss of consciousness and, if not treated, death in rare cases. These arrhythmias have also been observed in individuals with cardiac problems of other causes. So it is not certain that they are exclusively associated with non-compacted heart muscle.
A number of genes are thought to be associated with this condition. These are mainly genes that encode information important for the construction of the skeleton of the muscular cell. The identification of these genes became possible after it was noticed that a number of patients with non-compacted myocardium belonged to families where more members were affected to various extents.
There is no specific treatment for this condition at the moment. Key in the management of patients with features of the condition is the early recognition of the signs of cardiac dysfunction and prevention of complications. All medications and devices that have been used in heart failure have been used with good results in noncompaction cardiomyopathy too. In this sense the screening of family members of affected individuals is important and may alter the outcome of this condition.
The prognosis of people affected by this condition is difficult to predict and has to be individualised. In general it is associated with the degree of cardiac impairment. In severe cases it seems to be no different than the prognosis of any other heart failure. But increased awareness, the early detection of progression and the prevention of complications can really make the difference in the management of patients.
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Gene test developed for left ventricular noncompaction