Left ventricular noncompaction

Background

Left ventricular noncompaction or 'spongy myocardium' is a rare congenital cardiomyopathy that can be diagnosed at any age. It is characterised by a thin, compacted epicardial layer and an extensive noncompacted endocardial layer with prominent trabeculation and deep recesses that communicate with the left ventricular cavity, but not with the coronary circulation (1), probably due to an arrest of compaction during intrauterine life. It can be isolated or associated with other congenital diseases. Based on echocardiographic studies, reported prevalence is between 0.014% and 1.3% in the general population. Eventually, this condition can potentially lead to chronic heart failure, life-threatening ventricular arrhythmias and systemic embolic events. (2)

Echocardiography

Although there is no consensus on diagnostic criteria, echocardiography is the main diagnostic tool. In 2001, Jenni et al. (3) proposed criteria based on an end systolic ratio of noncompacted to compacted layers above 2. 

Segments involved are midventricular (especially inferior and lateral ones) and apical (Fig. 1) with evidence of direct blood flow from the ventricular cavity into deep intertrabecular recesses by colour Doppler (Fig. 2).

Figure 1: A case of left ventricular noncompaction involves midventicular and apical segments.

Figure 2: Colour Doppler showing direct blood flow from the ventricular cavity into deep intertrabecular recesses in a case of left ventricular noncompaction. 

Here are some practical tips when using echo:

• When looking for left ventricular noncompaction, image resolution, contrast and positioning of the focus in the apical region are crucial. 
• Differential diagnosis with thrombi, false tendons, apical hypertrophic cardiomyopathy, fibroma, obliterative processes, intramyocardial hematoma, cardiac metastases and intramyocardial abscesses must be considered. (4)
• In patients with suboptimal acoustic windows, intravenous ultrasound contrast agents are useful to better depict trabecular spaces (Fig 3).
• Much attention must be paid in order to:

1. Discard the presence of thrombus within the deep recesses; 
2. Rule out involvement of the right ventricle because of the common presence of multiple trabecula in this location.  

Cardiac magnetic resonance imaging 

Cardiac magnetic resonance imaging has become the method of choice to confirm or rule out left ventricular noncompaction because echocardiography cannot allow proper visualisation of the apex in some cases (Fig. 4).

Figure 4: Cardiac magnetic resonance imaging of a case of left ventricular noncompaction. 

Number of segments visualised : Thuny et al. (5) demonstrated that CMR is superior to 2D echocardiography in regards to the number of segments that can be analysed (especially during assessment of anterior, anterolateral and inferolateral segments) and the evaluation of the extent of the two-layered structure.

Criteria for diagnosis by CMR: Petersen et al. (6) described the criteria for the diagnosis by CMR: the ratio of noncompacted myocardium to compacted myocardium must be greater than 2.3 during the diastole (sensitivity of 86% and specificity of 99%). Later, Jacquier et al. (7) described another method to diagnose this entity: a trabeculated left ventricular mass above 20% of total mass with a sensitivity of 91.6% and a specificity of 86.5% is predictive of LVNC.

Correlation with clinical severity: In terms of correlation with clinical severity, Dodd et al. (8) showed that the amount of delayed trabecular hyperenhancement correlates significantly with LV ejection fraction (LVEF) and is an independent predictor of LVEF.

Prognosis, treatment and evaluations

The classical triad of complications - heart failure, ventricular arrhythmias and systemic embolic events -  are common in patients with advanced disease, although overall they are less frequently observed in recent studies than they were in initial reports. Oechslin et al. (9) reported that in a group of 34 adults with left ventricular noncompaction, the presence of higher final diastolic diameter of left ventricle, low ejection fraction, functional class III-IV (New York Heart Association), persistent or permanent atrial fibrillation and bundle branch block were related with high risk and poor prognosis, calling to consider the possibility of implantation of an automated cardiac defibrillator and evaluation for transplant. Mortality was similar in left ventricular noncompaction as with patients with nonischemic dilated cardiomyopathy  (three-year survival of 85% to 83%). (10)

Diagnosis calls for the study of family members, and maybe genetic counseling. Due to the high prevalence of neuromuscular disorders reported in patients with left ventricular noncompacton, neurological and musculoskeletal evaluations are also recommended. (11,12)

Unresolved issues

• Prevalence, frequent overestimation/underestimation.
• Definitive echocardiographic and CMR criteria for diagnosis.
• Prevalence of RV involvement and diagnostic criteria.
• Whether prognosis can be improved by early diagnosis-treatment.
• Comprehension of the poor genotype-phenotype correlation. 

Conclusion:

Left ventricular noncompaction is a rare cardiomyopathy that should always be considered as a possible diagnosis because of its potential complications. Echocardiography is the standard tool for diagnosis, and CMR is very useful to confirm or rule out this disease, especially when the apex is difficult to visualise. Nevertheless, there are still many questions regarding this disease that require further investigation and follow-up.