Surgery for Cardiac Disease in Small Animals: Current Techniques

Reference interval, longitudinal variability and reliability of activated clotting time in healthy dogs using a point-of-care analyser

BACKGROUND

Activated clotting times (ACTs) are used to screen for coagulopathies and monitor heparin therapy.

OBJECTIVES

To determine a reference interval (RI) for ACT in dogs using a point-of-care analyser, to quantify intra-subject within- and between-day variability, to quantify analyser reliability and inter-analyser agreement and to study the influence of a delay in measurement.

METHODS

Forty-two healthy dogs were included. Measurements were performed on fresh venous blood using the i-STAT 1 analyser. The RI was determined using the Robust method. Intra-subject within-day variability and between-day variability were quantified between baseline and 2 h (n = 8) or 48 h (n = 10) later. Analyser reliability and inter-analyser agreement were studied by duplicate measurements (n = 8) on identical analysers. The influence of measurement delay was studied before and after a delay of one analytical run (n = 6).

RESULTS

Mean, lower and upper reference limits for ACT were 92.9 ± 9.1, 74.4 and 111.2 s, respectively. Coefficients of variation of intra-subject within- and between-day variability were 8.1% and 10.4%, respectively, resulting in a significant between-day measurement difference. Analyser reliability assessed by the intraclass correlation coefficient and coefficient of variation were 0.87% and 3.3%, respectively. Significantly lower ACT values were observed after a measurement delay compared to direct analysis.

CONCLUSIONS

Our study provides an RI for ACT in healthy dogs using the i-STAT 1 and suggests low intra-subject within- and between-day variability. Analyser reliability and inter-analyser agreement were good; however, analysis delay and between-day differences could significantly influence ACT results.

Pulmonary artery banding in a cat with a perimembranous ventricular septal defect and left-sided congestive heart failure

CASE DESCRIPTION A 6-month-old sexually intact male domestic shorthair cat was referred for evaluation of a heart murmur and ventricular septal defect (VSD). CLINICAL FINDINGS Physical examination revealed a grade 5/6 right apical systolic heart murmur. Findings on thoracic radiography were consistent with moderate right and left ventricular enlargement, left atrial enlargement, and enlargement of the pulmonary arteries and veins; an interstitial pulmonary pattern was also evident. Echocardiography revealed a perimembranous VSD with left-to-right shunting combined with trace mitral valve regurgitation. The cat later developed a dry cough, the intensity of the heart murmur increased to grade 6/6, and signs of left-sided congestive heart failure developed. TREATMENT AND OUTCOME Medical treatment included enalapril maleate and furosemide. When the cat's condition worsened despite medical treatment, palliative pulmonary artery banding was performed. During surgery, blood pressure in the pulmonary artery was measured with a pulmonary artery catheter, and pulmonary artery banding was successfully achieved with a polytetrafluoroethylene band and hemoclips. The pulmonary-to-systemic blood flow ratio was reduced from 3 to 1.5, and signs of congestive heart failure resolved within 2 weeks after surgery. CLINICAL RELEVANCE Findings suggested that cats with a VSD and pulmonary-to-systemic flow ratio > 3 or with congestive heart failure attributable to a VSD could be considered candidates for palliative pulmonary artery banding to alleviate clinical signs. However, further investigation into long-term prognosis with objective outcome measurements and with multiple cases is needed. (J Am Vet Med Assoc 2019;254:723-727).

The mechanobiology of mitral valve function, degeneration, and repair

In degenerative valve disease, the highly organized mitral valve leaflet matrix stratification is progressively destroyed and replaced with proteoglycan rich, mechanically inadequate tissue. This is driven by the actions of originally quiescent valve interstitial cells that become active contractile and migratory myofibroblasts. While treatment for myxomatous mitral valve disease in humans ranges from repair to total replacement, therapies in dogs focus on treating the consequences of the resulting mitral regurgitation. The fundamental gap in our understanding is how the resident valve cells respond to altered mechanical signals to drive tissue remodeling. Despite the pathological similarities and high clinical occurrence, surprisingly little mechanistic insight has been gleaned from the dog. This review presents what is known about mitral valve mechanobiology from clinical, in vivo, and in vitro data. There are a number of experimental strategies already available to pursue this significant opportunity, but success requires the collaboration between veterinary clinicians, scientists, and engineers.

Mitral valve repair in dogs

Prognosis for dogs with severe mitral regurgitation is poor with medical therapy alone. Open surgical mitral valve repair consisting of circumferential mitral annuloplasty and artificial chordal replacement confers durability and improved long-term clinical outcome without a need for long-term antithrombotic therapies. This approach has been successfully used in canine patients, including small-breed dogs. Methods for mitral valve repair applicable to small dogs are described.