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Am J Physiol Heart Circ Physiol 288: H1179-H1185, 2005. First published October 21, 2004; doi:10.1152/ajpheart.00045.2004
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Pronounced HR variability after exercise in inferior ischemia: evidence that the cardioinhibitory vagal reflex is invoked by exercise-induced inferior ischemia

Nobuhiro Tahara,1 Hiroshi Takaki,2 Atsushi Taguchi,1 Kazuhiro Suyama,1 Takashi Kurita,1 Wataru Shimizu,1 Shunichi Miyazaki,1 Toru Kawada,2 and Kenji Sunagawa2

1Division of Cardiology, Department of Medicine, National Cardiovascular Center, and 2Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan

Submitted 22 January 2004 ; accepted in final form 19 October 2004

Potent cardioinhibitory vagal reflex resulting in bradycardia and hypotension has been observed under particular conditions of transmural inferior ischemia and its reperfusion, such as those observed with acute infarction. However, whether exercise-induced ischemia with ST depressions that is subendocardial and that might be recurrently experienced in daily activities can evoke this reflex remains unknown. In patients with exercise-induced ST depressions due to either inferior [right coronary artery stenosis (RCA), n = 52] or anterior ischemia [left anterior descending artery stenosis (LAD), n = 51], we evaluated post exercise vagal activity (from 0 to 6 min) by the time constant of heart rate (HR) decay and HR variability by 30-s averages of the absolute values of successive RR interval differences ({Delta}RR). Exercise parameters were similar between groups. The time constant was slightly but significantly shorter in RCA than LAD patients (79 ± 24 vs. 93 ± 29 s, P < 0.01). More significantly, {Delta}RR early after exercise (0.5–2.5 min) was approximately twofold greater in RCA than LAD patients (from +76 to +118%, P < 0.001), indicating pronounced vagal activity stimulated by inferior ischemia. Revascularization prolonged the time constant (P < 0.05) and attenuated recovery {Delta}RR in RCA patients (P < 0.05, n = 10) but did not change both parameters in LAD patients (n = 12). As well as acute inferior infarction, exercise-induced inferior subendocardial ischemia, which might recurrently occur in daily activities, activates the cardioinhibitory reflex. These new findings must be taken into account in interpreting vagal activity in patients with coronary artery disease.

heart rate variability; vagus nerve; coronary artery disease


Address for reprint requests and other correspondence: H. Takaki, Dept. of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan (E-mail: htakaki{at}res.ncvc.go.jp)






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