Blood flow in the hypertrophied right ventricular myocardium of unanesthetized ponies.

This research investigates the effects of right ventricular hypertrophy (an enlargement of the right lower chamber of the heart) on regional myocardial blood flow (blood flow in the heart muscle) and the coronary vascular reserve (the heart’s capacity to increase blood flow) in unanesthetized adult ponies.

Research Design and Subjects

• A total of 12 adult ponies were included in the study. Six out of the 12 were used as control subjects.
• The other half of the subjects had their main pulmonary artery deliberately constricted (using a banding method) between 35 to 90 days prior to the study, to induce right ventricular hypertrophy.

Method of Data Collection

• The researchers measured the regional myocardial blood flow using radio-nuclide-labeled microspheres, a technique that allows the tracking of blood flukes. Also, they administrated isoproterenol HCl intravenously at a dosage of 1 microgram per kilogram per minute, to observe the impacts on cardiovascular behavior.

Results

• In ponies with banded Pulmonary Arteries (PAs), there was a notable increase in right ventricular systolic pressure (147%), heart rate (88%), right ventricular tension-time index (279%) and right ventricular myocardial blood flow (137%) compared to the control group.
• The right ventricular coronary vascular resistance (the opposition to blood flow in the heart’s vessels) was found to be only 40% when compared to the control ponies.
• When isoproterenol was infused, it induced a significant increase in myocardial blood flow in all the ponies. However, in PA-banded ponies, the endo/epi flow ratio (measure of blood flow within the heart) fell sharply below 1.00 in both ventricular free walls.
• When looking at the resistance of the coronary vessels to the blood flow (RV coronary vascular resistance), in PA-banded ponies this decline was comparatively smaller, only 32% of that for control ponies.

Conclusion

• The researchers concluded that, unlike in Left Ventricular hypertrophy, the blood flow per unit mass in the hypertrophied Right Ventricle myocardium of resting adult ponies is much higher.
• This increased right ventricular perfusion takes place at the expense of a reduced right ventricular coronary vascular reserve. This may imply potential implications on the heart’s capacity to increase blood flow when it’s needed, like in periods of stress or exercise.