Late color duplex scanning diagnosis of the areas of endovascular intervention into arteries and lower extremity shunts

The purpose of the study was to assess the areas of balloon angioplasty (BAP) and stenting of lower extremity arteries and femoral, popliteal, mainly, in situ autovenous shunts, by using color duplex scanning (CDS) in the late period of a follow-up. Materials and methods. The CDS technique could diagnose 344 (64%) areas of BAP and stenting of lower extremity arteries and shunts. The echosemiotics of complications typical of a late period was determined. Based on the specified echosemiotics of late complications, the author detected 99 (28.8%) cases of hemodynamically significant complications: BAP and stenting area stenosis (n=25 (7.3%)); BAP area restenosis (reocciusion) (n=33 (9.6%)); stent restenosis (n=19 (5.5%), arterial stenosis proximal and distal to a stent (n=17 4.9%)), and stent breakage (n=5 (1.5%)). Hemodynamically insignificant complications were revealed in 90 (26.2%) cases: intimal dissection in 16 (4.7%) cases, BAP area restenosis in 35 (10%), stent restenosis in 15 (4.4%), and arterial stenosis proximal or distal to the stent and between the stents. In the late period following BAP and stenting aortoiliac patency was 87.50 + 3.18% during a mean follow-up o 27.58 + 1.50 months. In the late period, the patency of the superficial femoral artery (SFR) was 55.41 + 14.43% during a mean follow-up of 22.60 + 2.73 months, that of the popliteal artery (PA) was 67.34 + 15.98% during a mean follow-up of 43.08 + 5.81 months, that of shin arteries was 44.96 + 19.77% during a mean follow-up of 18.76 + 2.58 months, and that of shunts, was 40.89 + 18.47% during a mean follow-up of 23.32 + 2.29 months. Thus, changes caused by the progression of the underlying disease--atherosclerosis were found in the areas of BAP and stenting of lower extremity arteries and shunts. Stent breakage may be due to "metal deterioration" and the presence of a stent in the superficial femoral artery with greatest functional load on extremity movement and flexion. The blood flow spectrum mode recording a local hemodynamic shift with > 2.0-2.5-fold linear blood flow velocity increase in the complication area was leading in the operation of an ultrasound apparatuses in the differential diagnosis of hemodynamically significant and insignificant complications. The results of good late patency of the areas of BAP and stentming of SFR and PA may be accounted for by strict criteria for selecting patients for endovascular surgery, by taking into account the indications for and contraindications to TASC (2001). In our study, 20 endovascular reinterventions (repeated balloon angioplasty, additional stenting stent balloon angioplasty) in complicated areas were performed, which maintained and prolonged the function of segments. The detection of hemodynamically insignificant complications revealed patients who need further meticulous follow-up ultrasound studies.     

Endovascular operations on leg arteries

The paper presents the results color duplex scanning (CDS) diagnosis during 42 endovascular operations (40 balloon angioplasties and 2 stentings) on leg arteries with stenoocclusive changes. The operations were successful in 95.5% of cases, as evidenced by angiography and in 83.3% as shown by CDS; there were 7 (16.7%) cases of hemodynamic events, such as angioplastic site thrombosis, intimal dissection, and residual stenosis. Late follow-ups revealed 6 (16%) cases of hemodynamic events, such as angioplastic area thrombosis and reocclusion. CDS permitted evaluation of the patency of leg arterial endovascular intervention areas, which was 44.96+/-19.77% at a follow-up of up to 60 months (mean follow-up period 18.76+/-2.58). Two stents were patent within 24 months.     

X-ray morphology of coronary arteries in patients with arterial hypertension in late periods after endovascular treatment

An association of arterial hypertension (AH) and late angiographic outcomes of endovascular interventions was studied in coronary heart disease. Forty two patients with or without AH underwent repeated coronary angiography within 2 months after the procedure. The total number of restenoses was found to be significantly greater in patients with AH than in those without it. The diameter of restenoses was significantly smaller (70.2 +/- 24.7 vs 48.2 +/- 29.2%) and their area is significantly larger (82.6 +/- 19.6 vs 66.9 +/- 28.8). Absence probability of restenosis was significantly smaller in patients with AH (7 vs 27%); at the same time there was the greatest reduction in this probability in the first 8 months following the intervention.     

Ultrasound diagnosis in endoprosthesis of lower extremity arterial aneurysms with "Hemobahn"- and "Viabahn"-eluted stents

The paper presents the results of color duplex scanning (CDS) in 7 patients treated at the Unit of Vascular Surgery, Clinical Hospital No. 83, from 2002 to 2006, in whom 5 Hemobahn grafting stents and 2 Viabahm ones were implanted into the lower limb arterial aneurysms and the proximal anastomoses of the iliofemoral alloshunts "Gore-tex". A grafting stent was individually selected for each specific case. All the examinees were males. The patients' age was 60 to 70 years. The results of endovascular interventions were assessed, by analyzing color duplex scanning (CDS) of a grafting stent implantation area in early postoperative periods (days 1-3), further by the scheme following 1, 3, 6, and 12 months and then twice a year. Endovascular intervention areas were studied by the standard procedure on Logic-500 and Vivid-700 ultrasound apparatuses (USA) with a 7.5-MHz linear transducer and a 3.5-MHz convection transducer. In the postoperative period, multiprojection scanning was used to detect stent configuration impairments. According to the data of examination using the CDS technique, a surgical success was noted in 100% of cases. In all cases, stage, adequate aneurysmal stenting along with the restoration of the geometry of proximal anastomoses of iliofemoral alloshunts, iliac and superficial femoral arteries with exclusion of aneurysms from blood flow was diagnosed at a hospital stage. Follow-up ultrasonography revealed no changes in the area of endovascular intervention. Thus, as a highly informative, noninvasive technique, CDS can assess the results of implantation of grafting stents into the arteries and shunts of the lower extremities in both early and late postoperative periods.     

Cerebrospinal Fluid Shunts

Cerebrospinal fluid (CSF) shunt technology has undergone rapid advances in the past two decades. As a result, pediatricians and other primary care physicians are being asked with increasing frequency to provide care for persons with CSF shunts. Familiarity with the more common shunts is a prerequisite to intelligent management of shunt related problems. Physicians providing daily care must have carefully documented hospital records and operative notes available to them as well as information detailing the safe evaluation of shunt patency and function if they are to manage patients with CSF shunts properly. In addition, parents and guardians must be alerted to signs and symptoms related to shunt malfunction.     

Advanced Age and Disease Predict Lack of Symptomatic Improvement after Endovascular Iliac Treatment in Male Veterans

Background: Endovascular angioplasty and stent placement is currently the most frequent treatment for iliac artery occlusive disease. However, despite a successful endovascular procedure, some patients do not experience symptomatic improvement and satisfaction with their care. This study seeks to identify patient-related factors associated with lack of symptomatic improvement after endovascular iliac artery treatment in male veterans.Methods: Retrospective review of patients treated with endovascular methods for iliac artery occlusive disease between January 2008 and July 2012 at VA Connecticut Healthcare System. Symptomatic improvement on the first post-operative visit was evaluated, with bilateral treatments counted separately.Results: Sixty-two patients had 91 iliac arteries treated with angioplasty and stent placement. Forty-seven (52 percent) legs had critical limb ischemia, and 77 (85 percent) had at least two-vessel distal runoff. Angiographic success was 100 percent. Patient-reported symptomatic improvement at the first post-operative visit was 55 percent (50/91). Lack of symptomatic improvement correlated with older age (OR 1.09 [1.03-1.17], p = 0.008), presence of critical limb ischemia (OR 3.03 [1.09-8.65], p = 0.034), and need for additional surgical intervention (OR 5.61 [1.65-17.36], p = 0.006). Survival, primary and secondary patency, and freedom from restenosis were comparable between patients who reported symptomatic improvement and those who did not.Conclusions: Despite angiographically successful revascularization, patients who are older or have critical limb ischemia who are treated with isolated endovascular iliac artery intervention are more likely to require additional interventions and less likely to experience symptomatic improvement. These patients may need more extensive infra-inguinal revascularization than isolated iliac angioplasty and stent placement, despite a preserved ankle-brachial index. Quality of life needs to be measured with formal instruments after iliac artery endovascular treatment, especially to determine long term outcomes.     

Surgical management of portal hypertension.

Portal hypertension is frequently complicated by upper gastrointestinal tract bleeding and ascites. Hemorrhage from esophageal varices is the most common cause of death from portal hypertension. Medical treatment, including resuscitation, vasoactive drugs, and endoscopic sclerosis, is the preferred initial therapy. Patients with refractory hemorrhage frequently are referred for immediate surgical intervention (usually emergency portacaval shunt). An additional cohort of patients with a history of at least 1 episode of variceal hemorrhage is likely to benefit from elective shunt operations. Shunt operations are classified as total, partial, or selective shunts based on their hemodynamic characteristics. Angiographically created shunts have been introduced recently as an alternative to operative shunts in certain circumstances. Devascularization of the esophagus or splenectomy is done for specific indications. Medically intractable ascites is a separate indication for surgical intervention. Liver transplantation has been advocated for patients whose portal hypertension is a consequence of end-stage liver disease. In the context of an increasingly complex set of treatment options, we present an overview of surgical therapy for complications of portal hypertension.     

Endovascular brachytherapy in the prevention of vascular restenosis

Purpose: To evaluate the technical feasibility and efficacy of endovascular brachytherapy for prophylaxis of restenosis after femoropopliteal percutaneous transluminal angioplasty (PTA). Materials and methods: Ten patients with recurrence of stenosis in the femoropopliteal region underwent PTA followed by endovascular irradiation with Iridium-192 a high-dose rate after-loading technique. We used a single fraction of dose 12 Gy given in 3 mm from the source axis in the stenotic vessel segment. Results: During follow-up of 59–580 days restenosis occurred in four patients 111, 460, 472 and 580 days after irradiation. All other patients are without restenosis. No radiation-associated side effects were observed. Conclusions: Endovascular brachytherapy of restenosis in the femoropopliteal region is technically feasible, and may be done as a part of the PTA. These encouraging results open the possibility of reduction of restenosis by the present method.     

Arterial Surgery in Intermittent Claudication

The results of a survey of 302 operations in 277 patients during 1959-70 are presented, and an additional 69 operations during 1971 are included in the mortality figures. Operative mortality (1968-71) was 0·9% in 113 aortoiliac operations and nil in 96 femoropopliteal operations.Immediate patency rates on dismissal from hospital exceeded 95%, and the five-year patency rate for aortoiliac operations was just over 70% and for femoropopliteal operations 60%.     

Lactate kinetics at rest and during exercise in lambs with aortopulmonary shunts.

In a previous study [G. C. M. Beaufort-Krol, J. Takens, M. C. Molenkamp, G. B. Smid, J. J. Meuzelaar, W. G. Zijlstra, and J. R. G. Kuipers. Am. J. Physiol. 275 (Heart Circ. Physiol. 44): H1503-H1512, 1998], a lower systemic O2 supply was found in lambs with aortopulmonary left-to-right shunts. To determine whether the lower systemic O2 supply results in increased anaerobic metabolism, we used [1-13C]lactate to investigate lactate kinetics in eight 7-wk-old lambs with shunts and eight control lambs, at rest and during moderate exercise [treadmill; 50% of peak O2 consumption (VO2)]. The mean left-to-right shunt fraction in the shunt lambs was 55 +/- 3% of pulmonary blood flow. Arterial lactate concentrations and the rate of appearance (Ra) and disappearance (Rd) of lactate were similar in shunt and control lambs, both at rest (lactate: 1, 201 +/- 76 vs. 1,214 +/- 151 micromol/l; Ra = Rd: 12.97 +/- 1.71 vs. 12.55 +/- 1.25 micromol. min-1. kg-1) and during a similar relative workload. We found a positive correlation between Ra and systemic blood flow, O2 supply, and VO2 in both groups of lambs. In conclusion, shunt lambs have similar lactate kinetics as do control lambs, both at rest and during moderate exercise at a similar fraction of their peak VO2, despite a lower systemic O2 supply.     

Hemodynamics of patient-specific aorta-pulmonary shunt configurations

Optimal hemodynamics in aorta-pulmonary shunt reconstruction is essential for improved post-operative recovery of the newborn congenital heart disease patient. However, prior to in vivo execution, the prediction of post-operative hemodynamics is extremely challenging due to the interplay of multiple confounding physiological factors. It is hypothesized that the post-operative performance of the surgical shunt can be predicted through computational blood flow simulations that consider patient size, shunt configuration, cardiac output and the complex three-dimensional disease anatomy. Utilizing only the routine patient-specific pre-surgery clinical data sets, we demonstrated an intelligent decision-making process for a real patient having pulmonary artery atresia and ventricular septal defect. For this patient, a total of 12 customized candidate shunt configurations are contemplated and reconstructed virtually using a sketch-based computer-aided anatomical editing tool. Candidate shunt configurations are evaluated based on the parameters that are computed from the flow simulations, which include 3D flow complexity, outlet flow splits, shunt patency, coronary perfusion and energy loss. Our results showed that the modified Blalock-Taussig (mBT) shunt has 12% higher right pulmonary artery (RPA) and 40% lower left pulmonary artery (LPA) flow compared to the central shunt configuration. Also, the RPA flow regime is distinct from the LPA, creating an uneven flow split at the pulmonary arteries. For all three shunt sizes, right mBT innominate and central configurations cause higher pulmonary artery (PA) flow and lower coronary artery pressure than right and left mBT subclavian configurations. While there is a trade-off between energy loss, flow split and coronary artery pressure, overall, the mBT shunts provide sufficient PA perfusion with higher coronary artery pressures and could be preferred for similar patients having PA overflow risk. Central shunts would be preferred otherwise particularly for cases with very low PA overflow risk.     

Early results of endovascular treatment of chronic coronary occlusion in patients with ischemic heart disease

The early results of endovascular treatment of chronic coronary occlusion were studied. Immediate success rates were 67%. The factors that promote successful endovascular treatment in patients with this condition were as follows: less than 2-month disease duration, well-developed intersystemic collaterals, no "bridge" collaterals. Successful recanalization for chronic coronary occlusion improves the quality of life and bicycle ergometer test finding in patients, which reduces their needs of nitrates and beta-blockers. Coronary occlusion stenting yields better immediate angiographic results than does balloon angioplasty: residual stenosis and the minimum diameter of stenosis after stenting were 13.61 +/- 6.3% and 2.69 +/- 0.4 mm, respectively; those after balloon angioplasty were 23.1 +/- 8.1% and 2.31 +/- 0.37 mm, respectively.     

Can sites prone to flow induced vascular complications in a-v fistulas be assessed using computational fluid dynamics?

Arterio-venous fistulas (shunts between arteries and veins) are the preferred vascular access for hemodialysis. Despite their superior patency, compared with synthetic tubes and grafts, functional problems and inadequate flow rates are the common complications. Local flow conditions, in particular low and oscillating wall shear stresses (WSS), are central to vascular problems and a robust framework for analyzing flow conditions in vascular structures could provide an understanding of the mechanisms leading to vascular complications, such as stenoses, aneurisms, and thromboses.We hypothesize that a validated computational fluid dynamics (CFD) framework can be used to identify critical fistula configurations with elevated risk of complications. Therefore, the aim of the present study was to develop a CFD framework for analyzing fluid flow in complex vascular structures, such as arterio-venous fistulas validated by comparisons of in vitro volume flows with CFD results and flow fields from ultrasound scans with CFD simulations.Volume flows measured in vitro and CFD data differed quantitatively. However, good relative correlations exist between the data using logarithmic scales. Qualitatively, visual comparisons between ultrasound and CFD images showed good agreement between the two methods. In addition, WSS levels and the oscillatory shear index (OSI) were calculated and visualized on the model surface. The method was successfully validated and the method is deemed suitable for more thorough investigations into the field of vascular complications in a-v fistulas.     

The effects of dobutamine and dopamine on intrapulmonary shunt and gas exchange in healthy humans

The development of intrapulmonary shunts with increased cardiac output during exercise in healthy humans has been reported in several recent studies, but mechanisms governing their recruitment remain unclear. Dobutamine and dopamine are inotropes commonly used to augment cardiac output; however, both can increase venous admixture/shunt fraction (Qs/Qt). It is possible that, as with exercise, intrapulmonary shunts are recruited with increased cardiac output during dobutamine and/or dopamine infusion that may contribute to the observed increase in Qs/Qt. The purpose of this study was to examine how dobutamine and dopamine affect intrapulmonary shunt and gas exchange. Nine resting healthy subjects received serial infusions of dobutamine and dopamine at incremental doses under normoxic and hyperoxic (inspired O(2) fraction = 1.0) conditions. At each step, alveolar-to-arterial Po(2) difference (A-aDo(2)) and Qs/Qt were calculated from arterial blood gas samples, intrapulmonary shunt was evaluated using contrast echocardiography, and cardiac output was calculated by Doppler echocardiography. Both dobutamine and dopamine increased cardiac output and Qs/Qt. Intrapulmonary shunt developed in most subjects with both drugs and paralleled the increase in Qs/Qt. A-aDo(2) was unchanged due to a concurrent rise in mixed venous oxygen content. Hyperoxia consistently eliminated intrapulmonary shunt. These findings contribute to our present understanding of the mechanisms governing recruitment of these intrapulmonary shunts as well as their impact on gas exchange. In addition, given the deleterious effect on Qs/Qt and the risk of neurological complications with intrapulmonary shunts, these findings could have important implications for use of dobutamine and dopamine in the clinical setting.     

Does indomethacin affect shunt and its response to PEEP in oleic acid pulmonary edema?

We assessed hemodynamics, lobar perfusion, and shunts at base line 1.5 h after unilobar oleic acid edema, 15 min after indomethacin (10 mg/kg iv), and 15 min after positive end-expiratory pressure (PEEP) (10 cm) in 10 dogs. In 10 additional dogs (control) the same measurements were made but no indomethacin was administered. Shunts of the edematous lobe were: 10.6 +/- 6.3, 54.1 +/- 22.8, 30.8 +/- 16.6, and 12.4 +/- 6.3% for dogs administered indomethacin and 10.9 +/- 4.2, 53.8 +/- 13.1, 72.3 +/- 14.6, and 11.5 +/- 4.1% for the controls. Perfusions (% cardiac output) to the edematous lobe were 27.6 +/- 3.6, 14.6 +/- 2.0, 9.9 +/- 1.5, and 27.9 +/- 2.9% in the dogs administered indomethacin and 27.3 +/- 3.1, 14.0 +/- 1.7, 13.2 +/- 1.3, and 26.9 +/- 2.8% in controls. The decrease in lobar perfusion was similar before indomethacin with a further decrease in lobar perfusion and an increase in lobar vascular resistance 15 min after indomethacin. The increase in vascular resistance of the edematous lobe was three times that of nonedematous lobes after indomethacin (149.6 +/- 76% vs. 58.0 +/- 43%). Indomethacin, therefore, decreases shunt possibly by enhancing alveolar hypoxic vasoconstriction and does not block the improvement in shunt with PEEP.     

The effect of pancreatic and intestinal venous blood on hepatic atrophy and compensatory hyperplasia in the rat

Hepatotrophic effect of pancreatic and intestinal venous blood was studied in rats with mesocaval or distal splenocaval shunt following ligation of a branch of the portal vein supplying 70% of liver mass. Because 2/3 of liver mass was deprived of portal flow the nonligated liver lobes were not hypoperfused due to shunt procedure. During the first three postoperative days the DNA synthesis, mitotic index, and changes in relative weights were measured in both ligated (atrophied) and nonligated (compensatory hyperplasia) parts of the liver. It was found, that the restorative capacity of the liver existed in rats with selective portasystemic shunts. The stimulus to growth was greater in lobes supplied by intestinal venous blood compared to those perfused by pancreatic effluent. The increase in DNA synthesis occurred in lobes undergoing atrophy and the intensity of this response was also dependent on type of shunt since recirculation of intestinal blood by way of the hepatic artery inhibited atrophy to a greater extent than pancreatic venous effluent. Although the patency of arterial branches was confirmed the ligated lobes showed necrotic lesions. Systemic recirculation of intestinal venous blood far more inhibited necrosis than pancreatic venous blood.     

Factors affecting perfusion distribution in canine oleic acid pulmonary edema

Factors affecting perfusion distribution in oleic acid pulmonary edema were examined in 28 anesthetized open-chest dogs. Sixteen had unilobar oleic acid edema produced by left lower lobe pulmonary artery infusion of 0.03 ml/kg of oleic acid, and 12 had the same amount of edema produced by left lower lobe endobronchial instillation of hypotonic plasma. Lobar perfusion (determined from flow probes) and lobar shunt (determined from mixed venous and lobar venous blood) were measured at base line, 1.5 h after edema, and 10 min after 10 cmH2O positive end-expiratory pressure (PEEP). Fourteen dogs (8 oleic acid, 6 plasma) received sodium nitroprusside (11.72 +/- 7.10 micrograms X kg-1 X min-1). Total and lobar shunts increased to the same extent in all animals. Lobar perfusion decreased by 49.8 +/- 4.8% without nitroprusside and 34.0 +/- 3.6% with nitroprusside in the oleic acid group, corresponding values being 40.3 +/- 0.8% and 26.4 +/- 1.7% in the hypotonic plasma group. PEEP returned perfusion and shunt to base line. In oleic acid edema, most of the decreased perfusion results from mechanical effects of the edema, a smaller fraction results from other vascular effects of the oleic acid, and approximately 30% is reversible by nitroprusside. PEEP normalizes the perfusion distribution.     

蛛网膜下腔出血合并脑积水的治疗方法探讨

目的:探讨蛛网膜下腔出血(SAH)合并脑积水的治疗方法。方法:回顾性分析31例SAH合并脑积水患者的临床资料,除常规脱水、防治血管痉挛、营养神经等治疗方法外,其中10例给予行脑室-腹腔分流术,21例行侧脑室外引流术,对比分析两种治疗方案的利弊。结果:10例脑室-腹腔分流术患者9例手术效果良好,术后复查颅脑CT显示脑室明显减小,间质水肿消失,1例患者术后1月内再次出现脑积水,给予行同侧分流管探查再通、对侧脑室-腹腔分流术,术后效果良好,颅脑CT示脑室减小。21例行侧脑室外引流术患者,术后感染2例,全部患者均术后7天内拔除引流管,术后1月9例复发脑积水,给予再次行脑室-腹腔分流术,术后效果良好。结论:在手术指征明确的情况下,早期给予SAH合并脑积水患者行脑室腹腔分流术,分流管堵塞可能性小,术后感染发生率低,临床效果令人满意。     

脑室—腹腔分流术后感染26例诊治分析

目的探讨脑室—腹腔分流术后感染的早期诊断和治疗原则。方法回顾性分析26例脑室—腹腔分流术后感染病例的诊断和治疗办法,所有病例均进行血液和脑脊液的培养及影像学检查。结果 2例死于感染并发症,2例感染复发,21例患者重新安装分流装置,3例病情较轻的患者经分流泵及鞘内给药后痊愈。结论脑室—腹腔分流术后的早期诊断非常重要,一些非特异性的症状和体征需引起重视。对于感染的病例,及时移除分流装置,同时行脑室外引流冲洗和脑室内注药,当脑脊液达到无菌状态后重新植入分流装置是行之有效的办法。结果表明抗感染应首选万古霉素、第三代头孢菌素或改为美罗培南,待获得培养结果后根据药敏试验针对性用药。脑脊液培养以金黄色葡萄球菌和表皮葡萄球菌多见,经治疗再次培养结果均为阴性。     

Distribution of extrahepatic congenital portosystemic shunt morphology in predisposed dog breeds

ABSTRACT: BACKGROUND: An inherited basis for congenital extrahepatic portosystemic shunts (EHPSS) has been demonstrated in several small dog breeds. If in general both portocaval and porto-azygous shunts occur in breeds predisposed to portosystemic shunts then this could indicate a common genetic background. This study was performed to determine the distribution of extrahepatic portocaval and porto-azygous shunts in purebred dog populations. RESULTS: Data of 135 client owned dogs diagnosed with EHPSS at the Faculty of Veterinary Medicine of Utrecht University from 2001 - 2010 were retrospectively analyzed. The correlation between shunt localization, sex, age, dog size and breed were studied. The study group consisted of 54 males and 81 females from 24 breeds. Twenty-five percent of dogs had porto-azygous shunts and 75 % had portocaval shunts. Of the dogs with porto-azygous shunts only 27 % was male (P = 0.006). No significant sex difference was detected in dogs with a portocaval shunt. Both phenotypes were present in almost all breeds represented with more than six cases. Small dogs are mostly diagnosed with portocaval shunts (79 %) whereas both types are detected. The age at diagnosis in dogs with porto-azygous shunts was significantly higher than that of dogs with portocaval shunts (P < 0.001). CONCLUSION: The remarkable similarity of phenotypic variation in many dog breeds may indicate common underlying genes responsible for EHPSS across breeds. The subtype of EHPSS could be determined by a minor genetic component or modulating factors during embryonic development.