Safety of low-dose dobutamine stress test in coronary slow flow phenomenon

Purpose: To investigate the feasibility and safety of a low-dose dobutamine stress test in coronary slow flow phenomenon (CSFP) patients.Methods: One hundred and forty-two CSFP patients, and forty-four patients without CSFP or significant epicardial coronary stenosis who served as the control group, were retrospectively reviewed. All patients were infused intravenously with dobutamine at an initial infusion rate of 5 μg/kg/min which was then increased at 8-min intervals to 10, 15, and 20 μg/kg/min. Symptoms and echocardiography were monitored simultaneously.Results: Patient tolerance decreased as the doses of dobutamine increased. No termination of the test occurred without dobutamine or at the infusion rate of 5 μg/kg/min. Nonetheless, when the infusion rates were adjusted to 15 and 20 μg/kg/min, the incident of side effects reached up to 30.9 %, and a few patients experienced ST-segment depression in precordial electrocardiographic leads. There were no induced arrhythmias without dobutamine, while the incidence of arrhythmias was highest at the infusion rate of 20 μg/kg/min. Malignant arrhythmias such as ventricular fibrillation and sustained ventricular tachycardia, were not detected. No significant differences were showed in echocardiogram result for left ventricular ejection fraction (LVEF) between CSFP and control group (63.7±7.9 in the CSFP group, versus 64.3±7.2 in the control group; p = 0.63).Conclusion: A low-dose dobutamine stress test is safe and feasible in CSFP patients.

Abstract 17108: Natural History of Cardiomyopathy and Cardiac Stress Response in Young Dogs With Golden Retriever Muscular Dystrophy

Introduction: Duchenne muscular dystrophy (DMD) and the genetically homologous model, golden retriever muscular dystrophy (GRMD), are x-linked conditions that cause progressive muscle wasting and cardiomyopathy. We previously defined a late onset DMD-like dilated cardiomyopathy in adult GRMD dogs and aimed to extend that work to young dogs used for preclinical studies. The goal of this study was to characterize the early natural history and cardiac stress response of GRMD cardiomyopathy. Methods: A prospective imaging study was completed in 10 GRMD dogs and 8 age-matched normal littermates at 3, 6, and 12 months of age. Electrocardiography (ECG), echocardiography with speckle tracking, and cardiac magnetic resonance (CMR) with late gadolinium enhancement (LGE) and myocardial T1 mapping were assessed. In an effort to identify early subclinical evidence of cardiomyopathy, we conducted a dobutamine stress test in an additional subset of dogs (17 GRMD vs. 6 normal). Fractional shortening (FS) was assessed using echocardiography during dobutamine infusion (5-25 μg/kg/min) at 2 months of age, with follow up studies (4 GRMD vs. 6 normal) at 4.5 and 6 months. Results: Heart rate and ECG Q/R ratios (lead II, III, and aVF) were greater in GRMD dogs at 12 months (p<0.04 for all), and PR interval was shortened at 6 months (p=0.02). No systolic functional differences were seen between GRMD and normal dogs using echocardiography. No differences in circumferential strain were seen. CMR left ventricular end-diastolic volume, end-systolic volume, and myocardial mass were smaller in GRMD dogs from 6 months onward (p=0.014, 0.008, and 0.0013). LGE and extracellular volume calculated from T1 mapping did not differ on CMR. A diminished inotropic response, shown by a lower increase of FS (ΔFS), was seen in GRMD dogs during the dobutamine stress test (beginning at a dose of 5 μg/kg/min, 13.9±4.8% vs. 21.8±3.0%, p=0.003) at 2 months of age but not at 4.5 and 6 months. Conclusions: We demonstrated ECG changes and heart size differences in GRMD dogs as early as 6-12 months of age. While cardiac function was preserved, the inotropic response to dobutamine stress was blunted in 2-month-old GRMD dogs, potentially providing an early subclinical marker for DMD therapeutic research.

Feasibility and echocardiographic characteristics of a three-minute stage dobutamine stress test in healthy dogs

Introduction. Dobutamine stress test (DST) is used as a method of functional cardiac examination in human medicine due to dobutamine?s effect, which is similar to moderate physical exercise. The aim of this study was to assess the feasibility and echocardiographic characteristics of a conventional DST in dogs. Materials and Methods. Ten clinically healthy German Shepherd dogs were submitted to a conventional 3-minute stage DST protocol (the initial dose 7.5 ?g/kg/min was increased at 3-minute intervals by 5 ?g/kg/min until a maximum dosage of 42.5 ?g/kg/ min; the maximum DST duration was 24 minutes), which is used in human medicine. Dobutamine action was monitored by noninvasive diagnostic methods (simultaneously lead II electrocardiography and transthoracic echocardiography). Left ventricular echocardiographic parameters were measured at baseline and at the peak of DST. Results and Conclusions. The duration of conventional DST in dogs was 19.4?4.06 minutes. During the DST, sinus tachycardia was registered with no abnormalities of cardiac rhythm. The adverse effects registered in this study were excitement, panting and weakness. Interventricular septum thickness in systole (P=0.0093) and diastole (P=0.0080) increased significantly at the peak of DST. The left ventricular end-systolic dimension (P=0.0077) and the diastolic wall stress index (P=0.0125) decreased significantly at the peak of DST. A 3-minute stage with increased doses of dobutamine is a feasible method for the DST in dogs. The registered changes could be explained by the dobutamine effects through ?1 adrenergic receptors. This pharmacological stress test induces significant changes in left ventricular echocardiographic parameters in healthy adult dogs. Dogs exhibit transient signs like sinus tachycardia, excitement, panting and weakness during DST. Additional research on DST should evaluate the diagnostic value of this protocol in dogs suffering from cardiac disease.