Neurohormones in IWs with Atrial Fibrillation

Dr. Henry Green, III, veterinary cardiologist from Purdue University, led a team from the Purdue University School of Veterinary Medicine to characterize cardiovascular neurohormone levels in wolfhounds with primary atrial fibrillation (atrial fibrillation with no underlying heart disease). For this study, Dr. Green evaluated 32 Irish Wolfhounds to try to characterize what types of changes —if any—occurred in neurohormone levels in wolfhounds with AF. 

Atrial fibrillation in the absence of underlying cardiac disease is referred to as primary atrial fibrillation. This disease results in decreased ventricular filling secondary to loss of atrial contraction and subsequent decrease in cardiac output. 

Of the 32 IWs participating in this study, 15 (47%) had primary AF and 17 (53%) were in sinus (normal) rhythm. All cardiovascular medications were discontinued for at least two weeks prior to entry into the study. The neurohormones that were measured included plasma renin activity (PRA), brain natriuretic peptide (BNP), atrial natriuretic peptide (ANP), epinephrine (EPI), norepinephrine (NE) and aldosterone (ALD). Echocardiograms were performed on all study dogs. 

The study concluded that Irish wolfhounds with primary AF have significantly larger left atrial diameters and significantly higher plasma ANP levels than Irish Wolfhounds in sinus rhythm. ANP (atrial natriuretic peptide, or atriopeptin) is involved in the control of body water and sodium. It is released by cells in the atria of the heart, in response to signals of raised blood pressure, and it acts to reduce the water and sodium loads on the circulatory system, helping to return blood pressure to more normal levels. One of the reasons it is secreted is in response to stretching of the atria. One of the causes of stretching can be atrial fibrillation. The overall effects of ANP release is a reduction in blood volume, and therefore central venous pressure, cardiac output, and arterial blood pressure. It increases renal sodium secretion and excretion. It also increases lipolysis. ANP’s overall effect is to counter the blood pressure-raising effects of the renin-angiotensin system. 

These findings enabled Dr. Green and his co-investigators to conclude that primary AF in Irish wolfhounds is associated with markers of increased left atrial pressure, and possibly ventricular dysfunction. Further studies will be necessary to determine the chronic effect of primary AF on ventricular function.