Date Published: June 14, 2018
Publisher: Public Library of Science
Author(s): Leona Wall, Annika Mohr, Florenza Lüder Ripoli, Nayeli Schulze, Camila Duarte Penter, StephanOscar Hungerbuehler, Jan-Peter Bach, Karin Lucas, Ingo Nolte, Carlos E. Ambrósio.
Exercise intolerance is the first symptom of heart disease. Yet an objective and standardised method in canine cardiology to assess exercise capacity in a clinical setting is lacking. In contrast, exercise testing is a powerful diagnostic tool in humans, providing valuable information on prognosis and impact of therapeutic intervention. To investigate whether an exercise test reveals differences between dogs with early stage mitral regurgitation (MR) and dogs without cardiac disease, 12 healthy beagles (healthy group, HG) and 12 dogs with presymptomatic MR (CHIEF B1 / B2, patient group, PG) underwent a six-stage submaximal exercise test (ET) on a motorised treadmill. They trotted in their individual comfort speed for three minutes per stage, first without incline, afterwards increasing it by 4% for every subsequent stage. Blood samples were taken at rest and during two 3-minute breaks in the course of the test. Further samples were taken after the completion of the exercise test and again after a 3-hour recovery period. Measured parameters included heart rate, lactate and the cardiac biomarkers N-terminal pro-B-Type natriuretic peptide and cardiac Troponin I. The test was performed again under the same conditions in the same dogs three weeks after the first trial to evaluate individual repeatability. Cardiac biomarkers increased significantly in both HG and PG in the course of the test. The increase was more pronounced in CHIEF B1 / B2 dogs than in the HG. N-terminal pro-B-Type natriuretic peptide increased from 435 ± 195 to 523 ± 239 pmol/L (HG) and from 690 to 815 pmol/L (PG). cTnI increased from 0.020 to 0.024 ng/mL (HG) and from 0.06 to 0.08 ng/ml (PG). The present study provides a method to assess exercise-induced changes in cardiac biomarkers under clinical conditions. The increase of NT-proBNP and cTnI is more pronounced in dogs with early-stage MR than in healthy dogs. Results indicate that measuring the parameters before and after exercise is adequate and taking blood samples between the different stages of the ET does not provide additional information. Also, stress echocardiography was inconclusive. It can be concluded that exercise testing, especially in combination with measuring cardiac biomarkers, could be a helpful diagnostic tool in canine cardiology.
Exercise intolerance as the first symptom of mitral regurgitation (MR) in dogs evolves slowly and progressively and therefore often stays unnoticed until symptoms like coughing occur during exercise . In order to detect these changes as early as possible, submaximal exercise tests (ET) are commonly used in human cardiac patients for the assessment of functional capacity, prognosis, risk stratification and treatment options and for follow up-examinations in patients with heart diseases [2, 3]. Especially in unclear cases, the decision for or against therapeutic intervention is based on results of exercise tests and a post-exercise increase of cardiac biomarkers (CB) is of marked importance for the prognosis [4–7].
This study was approved by an institutional ethics commission (Lower Saxony State Office for Consumer Protection and Food Safety; 33.9-42502-05-14A484).
The submaximal ET was easy to perform and every dog was willing to run on the treadmill. All 24 dogs underwent the ET at a speed of 4.2 to 8 km/h and none of the ET had to be terminated due to an excessive increase of HR. Each dog showed increases of HR above 150 bpm or raised their resting HR by at least 40% at stage 2, indicating that the criteria for a minimum workload were met. One dog from the HG and 2 dogs from the PG refused to exercise further than stage 5 in both trials. With another dog from the HG, the test had to be stopped due to technical difficulties at stage 5 in the first trial.
The submaximal ET investigated in the present study introduces a method for assessing the physiological reaction of selected cardiovascular parameters under predefined exercise conditions in healthy dogs and dogs with presymptomatic MR (CHIEF B1 / B2). It yielded workload-dependent alterations in the parameters lactate, bicarbonate, HR, pH, cTnI and NT-proBNP and can be performed in a clinical setting. The most promising results include assessment of cardiac biomarkers.