Severe MAC increases shear stresses on particles traversing the mitral valve: an in vitro study

Funding Acknowledgements

Type of funding sources: None.

Background

  Mitral annular calcification (MAC) is a strong predictor of stroke but mechanism(s) are poorly defined.  Severe MAC can produce a gradient across the mitral valve (MV) and, when studied in vitro, disturbs normal flow across the valve resulting in increased viscous energy dissipation.

Purpose

  We hypothesized that severe MAC would increase shear stress on particles traveling across the MV into the left ventricle (LV).  Given that shear stresses cause platelet activation this might represent a mechanism by which MAC could increase stroke risk.

Methods

  A silicone model MV was created using a 3D TEE dataset. 3D printed calcium phantoms were incorporated into the valve simulate severe MAC. The valve was tested in a left heart duplicator under rest and exercise conditions and compared with a duplicate valve without the calcium phantoms. Fine particles suspended in a water/glycerol blood analogue allowed for measurement of vortex formation and shear stresses using particle image velocimetry (PIV).  Particle residence time (PRT) maps were created to assess how long blood particles would remain in the LV.  Particle residence index (PRI - ratio of remaining particles in LV/initial number of particles) is a more quantitative measure of how fast particles leave the LV.  These calculations were used to approximate viscous shear stresses on blood particles.  For each particle the induced viscous shear stress was evaluated for the entire duration of residence in the LV.

Results

  For the normal MV all released particles left the LV by the 3rd cycle; with severe MAC particles completely left the LV shortly after the 7th cycle.  PRI measurements confirmed that particles remained longer in the LV in the presence of severe MAC (figure 1).  MAC also induced a shift in the accumulated shear stress levels from the high range > 0.4 Pa.s and the low range < 0.1 towards the middle region (0.16-0.32 Pa.s, figure 2). As shear stress is reported for one cycle, one may expect MAC to lead to higher accumulated higher viscous stresses as particles reside in the LV for a longer time.

Conclusions

  In the presence of severe MAC blood particles remain longer in the LV and are exposed to greater cumulative shear stresses vs the normal situation.  Given that shear stress is known to cause platelet activation this may be a mechanism by which MAC increases risk of ischemic stroke. Abstract Figure 1  Abstract Figure 2

Morphological features of mitral annular calcification leading to systolic anterior motion of the mitral valve

Background

Systolic anterior motion (SAM) of the mitral valve (MV) can develop after mitral valve repair with placement of an annuloplasty ring. It is occasionally seen in patients with mitral annular calcification (MAC) but mechanisms have not been carefully delineated. Using 2-dimensional echocardiography we explored morphologic parameters which may contribute to SAM in patients with MAC.

Hypothesis

We hypothesized that in cases of MAC where SAM is present there would be anterior displacement of the valve by the posterior annular calcification.

Methods

From our echocardiographic database we identified 20 patients with severe MAC who also had SAM with definite septal contact. Each subject was paired with 2 controls free of MAC and 1 control with severe MAC but no SAM. All controls were matched for age, sex, BSA, and septal wall thickness (±1.5 mm). 2-D echocardiographic measurements were taken from the parasternal long-axis (PLAX), apical 3-chamber and apical 4-chamber views.

Results

MAC+SAM vs MAC no-SAM. Three notable differences were observed: MAC+SAM patients, as compared with MAC no-SAM, had a smaller left ventricular outflow tract (LVOT), longer anterior mitral leaflet, and greater displacement of the MV coaptation point towards the interventricular septum (Figure 1). Median values for these 3 factors were determined using the no-MAC controls; each MAC subject was then scored for number of factors exceeding those values. MAC+SAM patients had a mean score of 2.7 vs 1.1 for MAC no-SAM patients. By combining anterior mitral leaflet length and coaptation point-septal distance as a ratio we could effectively separate MAC+SAM vs MAC no-SAM when >0.9 with one exception (Figure 2). We also observed a smaller anteroposterior annular dimension in the MAC+SAM group.

MAC no-SAM vs no-MAC. Comparing these groups there were no differences in LVOT diameter or coaptation-septal distance; effective anterior mitral leaflet length was smaller in MAC no-SAM subjects vs no-MAC controls while anteroposterior dimension of the annulus was larger.

Conclusions

SAM develops in a subset of patients with severe calcification of the mitral annulus. These patients have a smaller anteroposterior annular dimension, possibly due to severe MAC. Other notable differences characterize MAC patients with SAM from those without. The LVOT is smaller, the effective anterior mitral leaflet length is longer, and the point of leaflet coaptation is displaced towards the septum. Using the ratio of anterior mitral leaflet length/coaptation point-septal distance in this study sample effectively separated those MAC patients with SAM from those without.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

Canine urethral sphincter pressure profile under incremental inflation of an artificial cuff: a cadaver study

OBJECTIVES

To determine whether artificial urethral sphincter filling volume is proportional to peak pressure exerted on the urethra.

MATERIALS AND METHODS

Urethral pressure profilometry was performed in five female, medium-sized, mixed-breed canine cadavers following artificial urethral sphincter placement. Maximum urethral pressure was recorded following sequential incremental inflation of 0.15 mL and compared to baseline pressure and between dogs using two-way analysis of variance.

RESULTS

Artificial urethral sphincter placement in cadavers was associated with an increase in urethral pressure, which was significantly correlated with inflation volume. The correlation was non-linear and demonstrated considerable individual variation. Maximum urethral pressures after artificial urethral sphincter placement exceeded those reported in conscious continent dogs within a narrow volume range, in which a 0.15 mL infusion more than doubled maximal urethral pressures.

CLINICAL SIGNIFICANCE

Rapid increases in urethral pressure from the artificial urethral sphincter over a small range of filling volumes (0.15 mL increments) might explain why some clinical cases can become suddenly dysuric following incremental inflations. We suggest that smaller increments of filling (0.05 to 0.1 mL) may achieve finer pressure control.

Temporally separated bilateral anal sac gland carcinomas in four dogs

Anal sac gland carcinoma arising from the apocrine secretory epithelium in the anal sac wall, is locally invasive and highly metastatic. The majority of anal sac gland carcinomas are unilateral on presentation, but bilateral tumours have been identified. This case series presents the outcome of four unique cases of unilateral anal sac gland carcinoma which subsequently developed contralateral anal sac gland carcinoma 50 to 390 days after removal of the initial tumour. Median survival was 1035 days after initial diagnosis and 807 days after diagnosis of the second anal sac gland carcinoma.

A survey of surgical draping practices in small-animal practice in the UK

Veterinary practices in the United Kingdom were surveyed to compare their surgical draping practices with Royal College of Veterinary Surgeons (RCVS) accreditation tier and other surgery-related factors. Using descriptive statistics and logistic or ordinal regression analysis (where appropriate), the relationships between draping material and accreditation tier and other surgery-related factors were assessed. Procedures were categorised as short or long. Two hundred and sixty-nine surveys were completed. Reusable drapes were used in 66 per cent of practices. Antibiotics were administered routinely in 38 per cent of short and 93 per cent of long procedures. Practices accredited as a Veterinary Hospital (VH) were 6.3-7.2 (short and long surgeries, respectively) times more likely to use disposable drapes, when compared with non-accredited practices. Use of dedicated surgical attire, draping the whole animal/table, and routine antibiotic usage were also positively correlated with disposable drape usage. Fifty-one per cent of practices rated infection rate as most important when choosing drape material. 'Best practice' techniques are associated with lower importance given to infection rate, and higher importance given to financial cost, when choosing drape material. Disposable drape use correlates with RCVS accreditation and with other aspects of surgical technique. Importance ratings awarded correlate with best practice procedures. Clinical relevance 'Best practice' draping procedures, that are not governed by RCVS accreditation scheme, are also more frequently performed in accredited VHs.

Relationship between pharyngeal conformation and otitis media with effusion in Cavalier King Charles spaniels

Otitis media with effusion (OME) is a common incidental finding in otherwise normal Cavalier King Charles spaniels (CKCS). In this study, measurements made on MRI were used to determine whether there was an association between OME and brachycephalic conformation. The results confirm that association and also demonstrate that, in CKCS, greater thickness of the soft palate and reduced nasopharyngeal aperture are significantly associated with OME. These results suggest that auditory tube dysfunction and OME may represent a previously overlooked consequence of brachycephalic conformation in dogs.

Preputial urinary diversion to treat urine soaking during urination in a dog

A young dog was presented with a history of adopting an unusual posture to urinate, resulting in urine soaking of the ventral abdomen and caudal forelimbs. The dog was initially treated surgically with cranial advancement of the prepuce, which did not resolve the problem. Further surgery was then successfully carried out to create a more caudal preputial orifice, which angled the penis ventrally when extruded, directing urine away from the body. At follow-up clinical examination, the dog was clinically normal.

Rupture of the cranial pubic tendon in the cat

Seven cats with rupture of the cranial pubic tendon (CPT) were presented to the authors between 1992 and 2001. The causal aetiology was unclear in each case. Diagnosis was made on physical examination (five animals) or surgical exploration (two animals). Concurrent injuries were present in four cats, including injury to the urinary tract and musculoskeletal system. All ruptures were surgically explored and primary repair of the CPT rupture was performed in five cats. Repair was not possible in two cats, and follow-up examination showed that scar tissue had apparently formed to support the deficit. All cats were asymptomatic at follow-up examination. The prognosis for CPT rupture in the cat is favourable.

Molecular cloning of resistance genes and architecture of a linked gene cluster involved in biosynthesis of oxytetracycline by Streptomyces rimosus

The isolation of mutants of Streptomyces rimosus which were blocked in oxytetracycline (OTC) production was described previously. The genes for the early steps of antibiotic biosynthesis mapped together. Genomic DNA fragments of S. rimosus which conferred resistance to OTC and complemented all of these non-producing mutants have been cloned. The cloned DNA is physically linked within approximately 30 kb of the genome of S. rimosus. The gene cluster is flanked at each end by a resistance gene each of which, independently, can confer resistance to the antibiotic. In OTC-sensitive strains of S. rimosus, the entire gene cluster including both resistance genes has been deleted. Complementation of blocked mutants by cloned DNA fragments in multi-copy vectors was often masked by a secondary effect of switching off antibiotic production in strains otherwise competent to produce OTC. This adverse effect on OTC production was not observed with recombinants using low copy-number vectors.