Right Pulmonary Artery Distensibility Index in Heartworm Infected Dogs: Are the Different Methods Leading to Same Results?

SIMPLE SUMMARY: Dirofilaria immitis infection in dogs induces damage to pulmonary arteries, which in turn, if severe enough, can lead to pulmonary hypertension and clinical signs of right-sided congestive heart failure. The initial vascular damage results in progressive reduction of the elastic properties of the vessel wall and consequent loss of its distensibility. Therefore, the reduced distensibility of the pulmonary artery wall becomes an early indicator of pulmonary hypertension. Pulmonary artery distensibility can be measured at the level of the right pulmonary artery, using an echocardiographic technique, obtaining the so-called distensibility index. Several studies on the distensibility index have been reported in the veterinary literature, where different methods of measurements have been used. This study was conducted to determine whether the results obtained with the different methods are superimposable in terms of clinical information. The present work indicates that, although there is a statistical agreement between the results of the different tests, they cannot be used interchangeably from a clinical point of view. ABSTRACT: Canine Heartworm Disease (HWD) is mainly a pulmonary vascular disease. The reduction of the Pulmonary Artery Distensibility (PAD) is an early index of pulmonary vascular disease. Echocardiographic evaluation of the Right Pulmonary Artery Distensibility index (RPADi) is calculated as the percentage change in diameter of the right pulmonary artery (RPA) between systole and diastole. Historically, two main methods have been used for RPADi calculation: The Venco method and Visser method; however, different hybrid methods have also been used by other authors. Therefore, it could be difficult for a clinician to decide which method to apply and how to interpret the results based on the reference values reported. The aim of this study was to compare the RPADi obtained by five different techniques (Venco classic, Venco modified, Visser classic, Visser modified 1, and Visser modified 2). The study design was a retrospective, single center, observational study. Forty-seven client-owned dogs were included. The measurements were performed off-line as an average of three consecutive cardiac cycles by a single investigator blinded to the dogs’ diagnosis. The RPADi was satisfactorily obtained by all methods in all dogs. Intra-observer measurement variability was clinically acceptable both for systolic and diastolic measurements. Although the Bland–Altman test showed a statistical agreement between the various methods used to calculate the RPADi, these methods cannot be used interchangeably in a clinical setting. Instead, the measurement method and reference values should always be specified.