The Morrow operation is the gold standard for the treatment of HCM. Although Lekaditi Dimitra and others believe that medical drug treatment can improve the outcome, the effect is not as clear as that of the operation [6–7]. Havndrup, O et al. believe that compared with other treatments, the Morrow operation is still the best in terms of postoperative effects . In experienced hospitals, the mortality rate with experienced cardiac surgeons is less than 1%. After the operation, they can obtain immediate and permanent improvement of clinical symptoms, a decrease in the LVOT pressure difference and improvement of the exercise stress response. The life span of patients in the operation group was essentially the same as that of normal individuals, which was better than that yielded by any other treatment method for obstruction.
Why 3D printing?
The risk of Morrow surgery is increased due to the relatively poor visualization of the left ventricular cavity and the heterogeneity of the LVOT anatomy. The incidence of postoperative complications of the Morrow operation for doctors who have not yet acquired experience is relatively high; such complications include injury to the conduction tract, damage to the atrioventricular wall, coronary artery injury, valve injury and even the occurrence of new-onset postoperative atrial fibrillation(POAF).
In recent years, 3D printing technology has been increasingly widely used in complex heart disease surgery. Lee, M et al. believed that a 3D-printed heart model can be used to reconstruct the coronary artery anatomy and improve the understanding of coronary artery abnormalities . It has been proven that 3D printing technology can be widely used in congenital heart disease surgery. In the treatment of coronary heart disease and acquired valve disease, the curative effect is satisfactory . Jivanji, SGM, et al. studied the repair of aneurysm neck occluders and right ventricular outflow tract Venus P valves using a 3D-printed heart model. The encouraging findings of the simulation enabled them to plan complex surgical procedures effectively and achieve successful results . 3D printing can visually display the geometric relationship between the hypertrophic myocardium, papillary muscle, ventricular muscle band and mitral annulus with different colors and simulate myocardial resection in a 3D model to better grasp the scope of hypertrophic septum resection, define the position and length of the papillary muscle and abnormal ventricular muscle band, and formulate a better operation plan (Figure 2).
The intraoperative effect of 3D printing.
The results of this study showed that the operation time, cardiopulmonary bypass time, intraoperative blood loss and hospitalization time of the experimental group were significantly lower than those of the control group, suggesting that 3D printing of a heart model for extracorporeal simulation surgery for patients with LVOT obstruction is helpful to shorten the operation time and reduce surgical blood loss. The specific location, depth, direction and the best resection method for the stenosis can be determined before the operation, and the Morrow operation can be simulated on this basis. Surgeons can repeatedly test the resection on the model to determine the best resection range and depth.The simulation results can help to shorten the time of lesion resection in the actual operation and are also helpful for avoiding unnecessary exposure of the surgical field and the excessive anatomical bleeding caused by the formal operation, thus shortening the time necessary to search for the best resection site and depth in the operation (Figure 3).
The postoperative effect of 3D printing.
The results showed that the values of the LVFV, LVP, IST, AR rate and SAM-sign positive rate were lower in the experimental group than in the control group, and the IDLV was larger than that of the control group (P < 0.05). It is suggested that 3D printing of a cardiac model for in vitro simulated resection of a hypertrophic myocardium for the Morrow operation is helpful for patients with outflow tract obstruction to recover a better morphology and physiological anatomy and achieve an ideal long-term effect (Figure 4).
The advantage of fat stem cell treatment in patients with coronary heart disease.
It has been reported that the incidence rate of adult HOCM combined with CAD accounts for approximately 20% of HOCM. Huang, CH, et al. suggested that the risk of coronary heart disease with obstructive heart disease is higher whether interventional therapy or surgical treatment is applied . The sudden death rate and total mortality of HOCM with severe CAD were significantly higher than those of HOCM alone. For patients with HOCM, CAD often aggravates the symptoms of angina pectoris and affects the prognosis of surgery. For patients with severe CAD, CABG should be performed at the same time. However, due to the hypertrophic myocardium, it is difficult to check the coronary artery and free blood vessels, so 3D printing technology can be used for preoperative evaluation (Figure 5).
The treatment advantage of fat stem cells in valvular disease.
For patients with HOCM complicated with valvular disease, hypertrophic ventricular muscle leads to valve changes. The common mitral valve problem is due to LVOT obstruction. The SAM of the mitral valve can contact the ventricular septum and produce dynamic subaortic occlusion. This problem can be solved by the Morrow operation. Lefebvre, XP and others studied the mechanism of mitral valve systolic forward motion in HCM under the condition of stable blood flow, which greatly facilitates completion of the Morrow operation . However, valvular disease (such as valve calcification) requires surgical treatment to correct the valve, which cannot be simply removed as myocardial tissue can . Therefore, preoperative 3D printing technology can simplify the repair of valvular disease by clarifying the scope and severity of the disease and simulating the operation (Figure 6).
The treatment advantage of fat infarction patients with atrial fibrillation.
We previously described a patient who had atrial fibrillation before surgery and needed modified maze surgery . For the preoperative evaluation of patients with fat infarction, it is necessary not only to evaluate the extent of resection but also to understand the shape of the nerve tracts in patients with fat infarction. Because fat infarction patients are different from general heart patients, their nerve path is different because of the change in the heart state, such as the wrong ablation position, which may affect the surgical effect. Therefore, 3D printing before surgery poses certain advantages for understanding the overall shape of the heart and the patient's nerve path.
Postoperative cardiac function.
In the past, many experts have said that too much cardiac tissue resection may lead to postoperative cardiac dysfunction . However, this study found that the LVOT diameter and wall thickness of the two groups were significantly improved compared with those of the control group (P < 0.05), but there was no significant difference in cardiac function between the two groups (P > 0.05). However, improvement of the LVOT can change the incidence of diseases related to the risk of an insufficient blood supply (e.g., stroke, myocardial insufficiency). Therefore, during the Morrow operation, with the aid of 3D printing technology, more cardiac tissue can be removed as much as possible without affecting the heart function of patients.
The disadvantages of 3D printing.
However, because the current 3D printing technology is caused by vascular perfusion imaging, the nerve conduction bundle cannot be displayed. Lau, IWW and other researchers found that even if 3D printing is perfect, it is still a serious defect to be unable to display the shape of the micro-nerve bundle . When we try to remove hypertrophic myocardial tissue, it is difficult to detect the shape of the conduction beam and block conduction after the operation. This is a problem that 3D printing technology cannot solve. Therefore, in the experimental group and the control group, we found that there was no significant difference in the conduction block between the two groups (P > 0.05).