Enhanced vagal modulation and exercise induced ischaemia of the inferoposterior myocardium

Heart rate variability and haemodynamic function in individuals with hypertrophic cardiomyopathy

OBJECTIVES

Heart rate variability (HRV) is a measure of cardiac autonomic function. This study: (1) evaluated the differences in HRV and haemodynamic function between individuals with hypertrophic cardiomyopathy (HCM) and healthy controls, and (2) determined the relationship between HRV and haemodynamic variables in individuals with HCM.

METHODS

Twenty-eight individuals with HCM (n = 7, females; age 54 ± 15 years; body mass index: 29 ± 5 kg/m2 ) and 28 matched healthy individuals (n = 7 females; age 54 ± 16 years; body mass index: 29 ± 5 kg/m2 ) completed 5-min HRV and haemodynamic measurements under resting (supine) conditions using bioimpedance technology. Frequency domain HRV measures (absolute and normalized low-frequency power (LF), high-frequency power (HF) and LF/HF ratio) and RR interval were recorded.

RESULTS

Individuals with HCM demonstrated higher vagal activity (i.e., absolute unit of HF power (7.40 ± 2.50 vs. 6.03 ± 1.35 ms2 , p = 0.01) but lower RR interval (914 ± 178 vs. 1014 ± 168 ms, p = 0.03) compared to controls. Stroke volume (SV) index and cardiac index were lower in HCM compared with healthy individuals (SV, 33 ± 9 vs. 43 ± 7 ml‎/beat‎/m², p < 0.01; cardiac index,2.33 ± 0.42 vs. 3.57 ± 0.82 L/min/m2 , p < 0.01), but total peripheral resistance (TPR) was higher in HCM (3468 ± 1027 vs. 2953 ± 1050 dyn·s·m2 cm-5 , p = 0.03). HF power was significantly related to SV (r = -0.46, p < 0.01) and TPR (r = 0.28, p < 0.05) in HCM.

CONCLUSIONS

Short-term frequency domain indices of HRV provide a feasible approach to assess autonomic function in individuals with HCM. Vagal activity, represented by HF power, is increased, and associated with peripheral resistance in individuals with HCM.

The Bezold-Jarisch Reflex in a Patient With Stanford Type A Acute Aortic Dissection

BACKGROUND

The Bezold-Jarisch reflex is a depressor reflex of the heart due to the preferential distribution of vagal nerves in the inferior wall of the left ventricle. We report a case of Stanford type A acute aortic dissection, in which coronary spastic angina caused the Bezold-Jarisch reflex in the acute phase.

CASE REPORT

A 53-year-old man presented with left chest pain and cold sweating. An electrocardiogram was normal and the high-sensitivity cardiac troponin T level was negative. A diagnosis of Stanford type A acute aortic dissection was made based on computed tomography (CT); there was no evidence of ischemic heart disease on coronary CT angiogram obtained simultaneously. While waiting for emergency surgical repair, chest pain worsened, followed by bradycardia and hypotension, along with ST-segment elevations in the inferior leads, all of which were resolved by conservative treatment. During surgery, no evidence to suggest an extension of the dissection to the ostium of the right coronary artery was observed. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: The present case highlights the importance of recognizing the Bezold-Jarisch reflex because this depressor reflex may require different management than other conditions.

The Bezold-Jarisch reflex in a patient with coronary spastic angina

Acute inferior myocardial damage can induce transient bradycardia and hypotension—the Bezold–Jarisch reflex, which is explained by the preferential distribution of vagal nerves in the inferior wall of the left ventricle. We report a 76‐year‐old man who showed a perfusion defect in the inferior wall with redistribution on exercise scintigraphy with thallium‐201. Of note, during exercise at an intensity of 100 watts, the patient's heart rate transiently decreased from 122 to 95 bpm in sinus rhythm, accompanied by ST‐segment depression. A diagnosis of coronary spastic angina was made since no stenotic lesions were observed on conventional coronary angiography.

Exercise-induced Atrioventricular Block with Coronary Artery Stenosis that Appeared Five Years after Bypass Surgery

A 68-year-old man with a history of coronary artery bypass surgery was referred to our hospital because of pre-syncope on effort. During a treadmill exercise electrocardiogram test, the patient developed advanced atrioventricular block associated with dizziness. Coronary angiography revealed significant stenosis of the right coronary artery, which had not existed at the time of the bypass surgery. We implanted drug-eluting stents in the stenotic lesion, and an exercise test showed resolution of the atrioventricular block. Exercise-induced atrioventricular block is rare, and it is necessary to distinguish it from ischemic heart disease, especially in patients with a history of coronary artery disease.

Sinus dysfunction after stent implantation in the right coronary artery immediately recovered after reflow in the sinus node artery

A 67-year-old man who had a history of syncope was admitted because of effort angina. The sinus node (SN) was the single blood supply from the right coronary artery (RCA). After we implanted 2 everolimus-eluting stents for RCA, slow-flow occurred and the SN artery was occluded, and junctional escape rhythm was sustained. After the wiring to the occluded SN artery, junctional escape rhythm immediately recovered to sinus rhythm, and the patient achieved continuous sinus rhythm and stable hemodynamics. Given that acute SN ischemia is a possible cause of sinus dysfunction, careful choice of a percutaneous coronary intervention strategy should be taken into consideration if the SN artery is the single blood supply from the RCA and if syncopal history is present.

Acute myocardial ischemia enhances the vanilloid TRPV1 and serotonin 5-HT3 receptor-mediated Bezold-Jarisch reflex in rats

The Bezold-Jarisch reflex is characterized by a sudden bradycardia associated with hypotension induced by the activation of the vanilloid TRPV1 and serotonin 5-HT(3) receptors. This reflex is associated with several health conditions, including myocardial infarction. The aim of the present study was to elucidate the influence of acute experimental myocardial ischemia on the reflex bradycardia induced by anandamide and phenylbiguanide, agonists of the TRPV1 and 5-HT(3) receptors, respectively. In urethane-anesthetized rats, the rapid iv injection of anandamide (0.6 μmol/kg) or phenylbiguanide (0.03 μmol/kg) decreased heart rate (HR) by about 7-10% of the basal values. Myocardial ischemia (MI) was induced by ligation of the left anterior coronary artery. The agonists were injected 5 min before MI (S(1)) and 10, 20 and 30 min thereafter (S(2)-S(4)). MI potentiated the anandamide-induced reflex bradycardia by approximately 105% at S(2) and 70% at S(3) but had no effect at S(4). This amplificatory effect of MI was virtually abolished by the TRPV1 receptor antagonist capsazepine (1 μmol/kg) and was not modified by the cannabinoid CB(1) receptor antagonist rimonabant (0.1 μmol/kg). MI also amplified the reflex bradycardia elicited by phenylbiguanide by approximately 110, 60 and 90% (S(2), S(3) and S(4), respectively), and this effect was sensitive to the 5-HT(3) receptor antagonist ondansetron (3 μmol/kg). In conclusion, our results suggest that acute myocardial ischemia augments the Bezold-Jarisch reflex induced via activation of TRPV1 and 5-HT(3) receptors located on sensory vagal nerves in the heart.

Chronotropic incompetence and autonomic dysfunction in patients without structural heart disease

AIMS

An attenuated heart rate response to exercise, termed chronotropic incompetence (CI), has been reported to be an independent predictor of cardiovascular mortality. We examined the change in autonomic function during exercise testing and correlated the results with CI.

METHODS AND RESULTS

Exercise testing using a bicycle ergometer was performed in 172 patients who had no evidence of cardiac disease. Chronotropic incompetence was defined as the failure to achieve 85% of the age-predicted maximum heart rate, heart rate reserve <80%, or chronotropic response index <0.80. We analysed the relationship between CI and the change in two components of heart rate variability during exercise testing: high-frequency (HF) component (0.15-0.40 Hz) as an index of vagal modulation and the ratio of low-frequency (LF) component (0.04-0.15 Hz) to HF component as an index of sympathovagal balance. Heart rate variability indexes before exercise were similar in patients with and without CI. Percentage changes after exercise in the ratio of LF to HF component were higher in patients with CI than in those without CI (84 +/- 15 vs. 41 +/- 16%, P < 0.05), whereas percentage changes in an HF component were similar in the two groups.

CONCLUSION

Our data suggested that CI in patients without structural heart disease was mainly caused by a pathophysiological condition in which sympathetic activation was not well translated into heart rate increase. Further study is needed to determine the post-synaptic sensitivity of the beta-adrenergic receptor pathway in relation to CI.

Vagal enhancement due to subendocardial ischemia as a cause of abnormal blood pressure response in hypertrophic cardiomyopathy

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) often develop myocardial ischemia in association with abnormal blood pressure response to exercise. Vagal nerves mediate cardioinhibitory stimuli, with little knowledge regarding vagal response to myocardial ischemia in patients with HCM.

METHODS

Exercise Tc-99m-tetrofosmin myocardial scintigraphy was performed in 59 HCM patients and 39 controls who had no evidence of cardiac disease. We examined how reversible regional perfusion abnormality and transient left ventricular cavity dilation, a parameter of subendocardial ischemia, are related to vagal modulation as assessed by coefficient of high frequency component variance (CCV(HF)) on heart rate variability. We then correlated the results with abnormal blood pressure response to exercise, defined as failed increase >or=25 mm Hg during exercise.

RESULTS

Regional perfusion abnormality and left ventricular cavity dilation were observed in 26 and 21 HCM patients, respectively. The percentage change of CCV(HF) from before to after exercise was higher in HCM patients with left ventricular cavity dilation than without or controls (5.2+/-9.8%, -23.5+/-5.7%, -14.5+/-5.5%, P=0.004). By contrast, the change of CCV(HF) was similar in HCM patients with regional perfusion abnormality, those without, and controls. The change of CCV(HF) was correlated with exercise-induced increase in systolic blood pressure (rho=-0.64, P<0.001); HCM patients with abnormal blood pressure response were characterized by a higher percentage change in CCV(HF) (50.0+/-18.3%).

CONCLUSIONS

Subendocardial ischemia provoked vagal enhancement in patients with HCM, which may be related to the development of abnormal blood pressure response to exercise.