The Mechanism of Adaptation of Left Atrial Stretch Receptors in Dogs with Chronic Congestive Heart Failure

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Chronic congestive heart failure (CHF) was induced in dogs by the construction of an aorto-caval fistula below the level of the renal arteries. Aorto-caval fistula dogs showed signs of CHF which included ascites, hind limb edema, and pulmonary congestion. Ventricular catheterization indicated a significantly higher left ventricular end diastolic pressure and lower maximum velocity of left ventricular pressure development/left ventricular end diastolic pressure in CHF dogs when compared to sham-operated controls. Heart weight/body weight ratios were significantly higher in CHF dogs. Electrophysiological recordings from medullated left atrial type B receptors from the cervical vagus indicated a depressed sensitivity of these receptors in CHF dogs when compared to sham-operated control dogs. For any given change in left atrial pressure, the discharge of left atrial receptors was significantly reduced in CHF dogs compared with sham-operated controls. The mechanism for this depressed sensitivity was investigated. Sonomicrometry of the left atrial appendage indicated a decreased compliance of the left atrial appendage in the dogs with chronic CHF. In addition, microscope examination of the complex unencapsulated receptor endings taken from the left atrial endocardium indicated a marked alteration in receptor morphology. A loss of the end arborization was the most typical finding. It is concluded that chronic CHF brought about by an aorto-caval fistula results in a depressed left atrial stretch receptor response and that both decreased left atrial compliance and structural alterations in the receptor endings may account for this depressed sensitivity.

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