Cardiac hemodynamics of the rainbow trout (Oncorhynchus mykiss) using simultaneous Doppler echocardiography and electrocardiography

Abstract

Using Doppler echocardiography and electrocardiography, we characterized cardiac hemodynamics, timing, and electromechanical function, and examined the effects of ventricular hypertrophy on systolic function in anesthetized rainbow trout. Atrial filling (D(SA)), ventricular filling (D(AV)), and ventricular ejection (D(VB)) accounted for 40-77, 13-27, and 22-41% of the cardiac cycle, respectively. Ventricular ejection occurred entirely during atrial filling and ended by the time the QT interval was 80% (SD=9%) completed. Sinoatrial (SA) flow was of longer duration (0.53+/-0.08 sec, mean+/-SD) and lower velocity (32+/-8 cm sec(-1)) than corresponding atrioventricular (AV, 0.19+/-0.02 sec; 87+/-8 cm sec(-1)) and ventriculobulbar (VB, 0.30+/-0.05 sec; 63+/-20 cm sec(-1)) values. Despite a wide range of heart masses, atrioventricular and VB valve dimensions were identical ( approximately 5.5 mm(2)). Ventricle mass (M(V)), but not relative ventricle mass (RVM), and cardiac cycle length were positively correlated (r(2)=0.57, P<0.001); thus, all time-dependent electrical/mechanical measures of cardiac function were significantly related to M(V), but not RVM. All rate-corrected (c) electromechanical event durations (except cD(SA)) and the systolic function index (cPEP (pre-ejection period)/D(VB)) were independent of RVM, suggesting the maintenance of cardiac functional capabilities across maturation stages (males) and different ventricle sizes (males and females). In summary, we define fundamental electrical and mechanical properties of the in vivo teleost myocardium under anesthesia, and report the maintenance of systolic function over a wide range of heart sizes for both sexes and maturation state of males. We also suggest that the short duration of ventricular emptying relative to the QT interval may provide a novel mechanism to adjust stroke volume and cardiac output in teleosts.

Sex-specific differences in cardiac control and hematology of sockeye salmon (Oncorhynchus nerka) approaching their spawning grounds

“…The difference in RVM between male and female sockeye (ϳ11%) in the present study was relatively small compared with reports of up to threefold larger ventricles in sexually mature male rainbow trout relative to mature females and immature males (14,32). In fact, the RVM of 0.13% for mature male sockeye salmon reported in the present study is ϳ25% lower than reports for mature male rainbow trout (20,32). For this reason, it is perhaps not surprising that the mean dorsal aortic blood pressure for sockeye salmon in the present study did not differ between sexes (4.9 -5.0 kPa).…”

Echocardiography and electrocardiography reveal differences in cardiac hemodynamics, electrical characteristics, and thermal sensitivity between northern pike, rainbow trout, and white sturgeon

“…The f H values, and the corresponding rhythmic activity of the cardiac pacemaker, were different for the three species at the acclimation temperature of 12°C, and at 20°C, when the fish were anesthetized with metomidate. The f H for anesthetized rainbow trout was well below that recorded for the other two species (Table ), and lower than the range reported previously for unanesthetized rainbow trout or those anesthetized with bicarbonate‐buffered MS‐222 at similar temperatures (i.e., ~40–90 bpm, Cotter et al, ; Cotter & Rodnick, ; Gamperl, Swafford, & Rodnick, ; Keen & Gamperl, ). It is well known that anesthesia with MS‐222 causes a transient increase in heart rate followed by prolonged bradycardia in rainbow trout (e.g., Lochowitz, Miles, & Hafemann, ).…”

“…ECG measurements were made from five cardiac cycles during stable heart rates for each fish. It is worth mentioning that a previous study by Cotter et al () demonstrated that maintaining a ventral‐side up body orientation for rainbow trout whereas irrigating their gills had minimal effects on both echocardiography and ECG measurements compared with ventral‐side down.…”

“…Analysis of hemodynamic patterns was performed on pulsed wave Doppler images using Image‐Pro Express 6.0 (Media Cybernetics, Inc., Rockville, MD). The duration of blood flow and peak flow velocities were derived from multiple Doppler images and waveforms as reported previously (Cotter et al, ). For each fish, hemodynamic measurements were obtained for three different cardiac cycles, and mean values were used in statistical analyses.…”

“…The rainbow trout has a pyramidal‐shaped ventricle comprised of a trabecular inner myocardium and an outer compact myocardial layer perfused via coronary arteries. The volume of the atrium is equal to, or greater than, the ventricle in this species, and atrial contraction (i.e., monophasic or active filling) appears to be the primary determinant of the ventricular filling during diastole (Cotter, Han, Everson, & Rodnick, ; Forster & Farrell, ). These contractile chambers are followed by an outflow tract (OFT) that is mainly composed of an elastic bulbus arteriosus, with the morphology of all chambers combining to form a heart that pumps smaller volumes at higher pressures (Tota & Gattuso, ).…”