Summary
Chronotropic and dromotropic responses to treadmill exercise were compared in conscious dogs prior to and following excision of the sinoatrial node (SAN). The initial junctional rhythm accompanying removal of the SAN region was replaced within hours to days by subsidiary atrial pacemaker (SAP) foci located in the inferior right atrium along the sulcus terminalis. With SAN intact, cardiac acceleration was immediate at onset of exercise and the tachycardia was directly proportional to work intensity. Atrioventricular (AV) conduction concurrently accelerated during exercise as manifest by shortening in P-R and atrioventricular (A-V) intervals. Following SAN excision, subsidiary atrial pacemaker foci likewise demonstrated prompt tachycardias during exercise, although heart rate was significantly reduced at rest and during steady state exercise. In the SAP state, tachycardia during exercise was related to work intensity and was mediated by changes in cardiac autonomic nerve activity. Combined propranolol-atropine blockade increased heart rate at rest in the SAP state, and significantly attenuated the tachycardia accompanying treadmill exercise. Following SAN excision the P-R (A-V) interval was significantly reduced in the resting animal. In response to exercise, AV conduction time decreased in the SAP state, though the absolute levels during steady state exercise were not significantly different from prior control runs with SAN intact. Blood pressure response to exercise was similar during both SAN and SAP states. We conclude that following an initial unstable period, SAP foci maintain adequate heart rate increases in response to dynamic exercise, primarily mediated via autonomic nerve regulation.
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References
Brooks CM, Lu HH (1972) The Sinoatrial pacemaker of the heart. Springfield: Thomas, pp 68–124
Donald DE, Samueloff SL (1966) Exercise tachycardia not due to blood-borne agents in canine cardiac denervation. Am J Physiol 211:703–711
Eyster JAE, Meek WJ (1921) The origin and conduction of the heart beat. Physiol Rev 1:1–43
Garrett HE (1966) Statistics in psychology and education. McKay, New York, p 291
Geesbreght JM, Randall WC, Brynjolfsson G (1970) Area localization of supraventricular pacemaker activity before and after SA node excision. Physiologist 13:202
Horwitz LD, Atkins JM, Leshin SJ (1974) Effect of beta-adrenergic blockade on left ventricular function in exercise. Am J Physiol 227:839–842
James TN, Bear ES, Frink RJ, Lang KF, Tomlinson JC (1970) Selective stimulation, suppression, or blockade of the atrioventricular node and his bundle. J Lab Clin Med 76:240–256
Jones SB, Euler DE, Hardie E, Randall WC, Brynjolfsson G (1978) Comparison of SA nodal and subsidiary atrial pacemaker function and location in the dog. Am J Physiol 234:H471-H476
Keith A, Flack M (1906) The form and nature of the muscular connections between the primary divisions of the vertebrate heart. J Anat Physiol 41:172–189
Randall WC, Talano JV, Kaye MP, Euler DE, Jones SB, Brynjolfsson G (1978) Cardiac pacemakers in the absence of the SA node. Response to exercise and autonomic blockade. Am J Physiol 234:H465-H470
Randall WC, Rinkema LE, Jones SB, Moran JF, Brynjolfsson G (1982a) Overdrive suppression of atrial pacemaker tissue in the alert, awake dog before and chronically after excision of the sinoatrial node. Am J Cardiol 49:1166–1175
Randall WC, Rinkema LE, Jones SB, Moran JF, Brynjolfsson G (1982b) Functional characterization of atrial pacemaker activity. Am J Physiol 242:H98-H106
Rozanski GJ, Lipsius SL, Randall WC (1983) Functional characteristics of sinoatrial and subsidiary pacemaker activity in the canine right atrium. Circulation 67:1378–1387
Seldinger SI (1953) Catheter replacement of the needle in percutaneous arteriography. Acta Radiol 39:368–376
Schwartz PJ, Stone HL (1979) Effects of unilateral stellectomy upon cardiac performance during exercise in dogs. Circ Res 44:637–645
Tipton CM, Carey RS, Eastin WC, Erickson HH (1974) A submaximal test for dogs: evaluation of effects of training, detraining and cage confinement. J Appl Physiol 37:271–275
Vatner SF, Pagani M (1976) Cardiovascular adjustments to exercise: hemodynamics and mechanisms. Prog Cardiovasc Dis 19:91–108
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Supported by NIH Grants HL 27595, HL 27664, HL 28205, and HL 32392
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Kim, K.S., Ardell, J.L., Randall, W.C. et al. Cardiac responses to exercise in the dog before and after destruction of the sinoatrial node. Europ. J. Appl. Physiol. 55, 253–258 (1986). https://doi.org/10.1007/BF02343796
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DOI: https://doi.org/10.1007/BF02343796