Surgical correction of DCRV often results in optimal outcomes with immediate relief of the RV pressure 6,21,22. When simple VSD is repaired without simultaneously correcting DCRV, tension could build up in the patched-up ventricle as hypertrophied muscular bundles continue to cause mid-cavity obstruction, but now without a defect to partially release the ventricular pressure 9. (Fig. 4) During surgery when the heart is flaccid, the job of spotting hypertrophied muscular bundles without prior notice or intraoperative transesophageal echocardiography may not be straightforward. Therefore, alerting surgeons of the possible presence of DCRV preoperatively becomes crucial.
Transthoracic echocardiography is considered the first-line screening examination for most cardiac diseases, including DCRV, although its accuracy may vary with different machines and operators 1,3,23. When the subinfundibulum is poorly visualized, and the diagnosis is inconclusive, CT might step in as a reliable alternative. Retrospective ECG-gated cardiac CT provides an animated, non-invasive demonstration of DCRV with objective measurements of chamber size changes.
The heart is a moving organ ever-changing its forms and shapes during a single cardiac cycle. Hypertrophic muscular bundles in DCRV are more easily spotted when contracted and thickened during systolic phases 1,11. (Supplementary video) While isolated DCRV is extremely rare, associated lesions are by contrast better demonstrated during diastolic phases 2,3,22. That is the reason why both systolic and diastolic images are essential for DCRV cases. In intricate details, retrospective ECG-gated cardiac CT shows the entire cardiac cycle, both systole and diastole. Identifying perplexity in congenital heart diseases has always been a strong suit for CT 1.
Since observing cardiac muscles is so crucial in DCRV, we created myocardial models tailored explicitly for the muscular portions of the cardiac chambers during CT post-processing. By rendering the muscles and not the chambers, you get this realist effect and it becomes so easy to spot unusual muscles. (Supplemental video) Our questionnaire results confirmed that myocardial models are effective image addendums that subjectively increase physicians’ confidence. It was also during this process that we discovered most hypertrophied muscular bundles in our DCRV cases (n = 21; 91.3%) occur just inferior to the level of the supraventricular crest in RV, not just anywhere randomly. This finding has seldomly been reported. Maron et. al first proposed the idea back in 1973 24 that DCRV might result from an acquired process in which the supraventricular crest slowly hypertrophied due to increased turbulent flow and shunting from VSD thus the high co-occurrence of DCRV and VSD. Our data surprisingly supported the hypothesis in that a markedly high degree of our cases had hypertrophied muscle bundles involving or just inferior to the supraventricular crest. Thus it was only reasonable that we chose to measure uniformly close to the level of supraventricular crest in RV. Other than that, as our myocardial model was able to directly demonstrate muscular thickness and morphology, it enables us to differentiate a normal supraventricular crest, which is supposed to be just an infolding of the RV wall 25, from a solid hypertrophied ridge in DCRV. Whereas with usual volume rendering, both show indentations in the luminal area and it wouldn’t be easy to tell if condensed muscles are present or the infolding is simply wider. (Fig. 5)
In recent decades, cardiac magnetic resonance has been gaining popularity for the evaluation of pediatric congenital heart diseases with no radiation exposure 26. However, cardiac magnetic resonance is often costly and time-consuming in Asia. For pediatric patients, this means heavy sedation or anesthesia in most cases, which is not always feasible due to tight schedules and shortage of anesthesia manpower. CT is often considered more cost-effective and accessible than cardiac magnetic resonance here, requiring only light sedation in the pediatric population at the cost of acceptable radiation exposure 16. We were thereby able to collect such a considerable amount of CT images in DCRV over the past 10 years. Of course, diagnosis of DCRV can always be made with cardiac catheterization, but it would be more invasive and costly than any of the image modalities 17
We were unable to recruit patients with isolated DCRV due to its rareness and therefore our data only applies to the majority who have concomitant simple VSDs. There is also the possibility of selection bias in that our patients might have exhibited more worrying clinical symptoms than average to warrant an operation, which explains the high DCRV occurrence rate. The presence of other cardiac lesions may also complicate the process of measurements. The results of this study, however, still prove CT to be a reliable modality in the diagnosis of DCRV.
Image post-processing, especially volume rendering, is a time-consuming process that can only be properly done manually, making it unrealistic to include myocardial models in every examination. Nevertheless, its potential to assist in surgical planning should not be underestimated.
In this study, we wish to raise awareness of DCRV in simple VSD cases among cardiologists, cardiothoracic surgeons, and radiologists. Right ventricular constrictive ratio showed promising diagnostic accuracy for the disease, with a cutoff value of less than 20.1%. We shared our observations regarding this disease on CT as an alternative to echocardiography. Our animated myocardial model brings about great potential in providing surgeons with a better perception of DCRV preoperatively.