1,721,002 research outputs found
Autonomic modulation during acute myocardial ischemia by low-dose pirenzepine in conscious dogs with a healed myocardial infarction: a comparison with beta-adrenergic blockade.
Full text linkExperimental and clinical evidence documents the ben- eficial effects of blocking sympathetic activity and modulating heart rate to reduce risk for lethal events in ischemic heart disease. Beside -adrenergic receptor blockade, vagal activation is a meaningful ap- proach but not yet easily attainable. Promising results were shown with low-dose atropine and scopolamine, but no follow-up was done because of significant adverse side effects. Pirenzepine is an atropine analogue approved to treat peptic ulcer disease in Europe that is de- void of central actions, which are mostly responsible for anti- muscarinic agents side effects. The vagomimetic action of IV low- dose pirenzepine was studied at rest under control conditions, at rest during acute coronary artery occlusion, and during exercise in con- scious dogs with a healed anterior myocardial infarction (MI). The effects of pirenzepine were then compared, by internal control analy- sis, with those of atenolol (1 mg/kg). Increasing doses of pirenzepine (from 0.01 to 1 mg/kg) were tested in 11 dogs at rest by measuring time and frequency domain heart rate variability (HRV). The most effective dose (0.1 mg/kg) was used in the study. At the most effective dose, pirenzepine increased all measures of time domain HRV by 40–50%. However, the vagomimetic action of pirenzepine was lost during exercise and brief ischemia and no anti-arrhythmic action was observed. Conversely, pirenzepine effectively modulated the heart rate increase during acute ischemia at rest with an effect comparable to that of atenolol. The vagomimetic action of pirenzepine in the acutely ischemic heart supports the possibility that this intervention may be helpful for chronic autonomic modulation in post-MI patients
Prediction of unexpected sudden death among healthy dogs by a novel marker of autonomic neural activity.
No full textWetestedthehypothesisthataparametercombining BRS and HRV could predict risk for ventricular fibrillation (VF) during a first ischemic episode in otherwise healthy dogs.
METHODS In 43 fully instrumented dogs, BRS and frequency do- main analysis of HRV were determined, as well as the occurrence (n 10, high-risk) or absence (n 33, low-risk) of VF during 2 minutes of myocardial ischemia superimposed on submaximal ex- ercise. TARVA (Tonic and Reflex Vagal Activity), expressed in units, is the parameter resulting from the multiplication of BRS by HF/LF (an index of tonic vagal activity).High-risk dogs had markedly lower TARVA values, re- flecting lower cardiac vagal activity, than low-risk animals (12 5 versus 56 43 units, P .001). The area under the receiver- operator characteristic curve for TARVA was 0.96 (95% confidence interval 0.86 to 0.99); its optimal cutoff had a 100% sensitivity and a 88% specificity with positive and negative predictive values of 71% and 100%, respectively.
CONCLUSION Differencesincardiacautonomicactivity,presentin healthy dogs, allow prediction of arrhythmic risk during a first isch- emic episode. Increased risk is associated with reduced vagal activity. If confirmed in humans, this finding would open the way to the identification of those apparently healthy subjects at risk for sudden cardiac death during their first episode of myocardial ischemia
Antifibrillatory efficacy of ersentilide, a novel beta-adrenergic and Ikr blocker, in conscious dogs with a healed myocardial infarction.
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A mechanism of cardiac pain suppression by spinal cord stimulation: implications for patients with angina pectoris.
No full textVagal reflexes and survival during acute myocardial ischemia in conscious dogs with healed myocardial infarction
No full textThe role of vagal tone and reflexes in the genesis of life-threatening arrhythmias was investigated in a clinically relevant animal model for sudden cardiac death. Forty-five dogs with a healed anterior myocardial infarction in which transient myocardial ischemia during exercise did not induce malignant arrhythmias were utilized for the study. They underwent a further exercise and ischemia test in which atropine (75 micrograms/kg) was injected before coronary artery occlusion. Novel occurrence of ventricular arrhythmia, or worsening of the type of arrhythmia present in the control test, occurred in 23 of 45 dogs (51%) and ventricular fibrillation occurred in 11 of 45 (24%, P = 0.001). Analysis of heart rate response to acute ischemia in the control test indicates that these 11 animals had powerful vagal reflexes during coronary artery occlusion, compared with the 34 survivors (-32 +/- 35 vs. +2 +/- 27 beats/min, P = 0.003). This study indicates that approximately 75% of animals resistant to ventricular fibrillation are characterized by weak sympathetic reflexes in response to acute myocardial ischemia. In the remaining 25% powerful vagal reflexes counteract concomitant reflex sympathetic hyperactivity, decrease heart rate, and are essential for survival
Do increases in markers of vagal activity imply protection from sudden death? The case of scopolamine.
No full textSympathetic-parasympathetic interaction and accentuated antagonism in conscious dogs
No full textThe heart rate response to vagal stimulation and the interaction with sympathetic activity was evaluated in conscious dogs at rest and during exercise; the latter was used as a tool to physiologically elevate sympathetic activity. In 20 dogs with a healed myocardial infarction and in 7 healthy dogs a bipolar electrode was chronically implanted around the right cervical vagus. Vagal stimulation (3 ms; 2.1 +/- 0.7 mA; 2, 4, 6, 8, 10, 12 Hz) was performed while dogs stood on the treadmill (heart rate 120 +/- 25 beats/min) and while they exercised (201 +/- 17 beats/min). Gradual increases of the frequency of vagal stimulation gradually enhanced the inhibitory effect on heart rate both before and during exercise. During exercise, heart rate reduction was significantly greater than that produced at rest at any frequency of stimulation (P less than 0.001). This difference widened as the frequency of stimulation increased and the interaction with or without the presence of exercise was significant (P less than 0.02). Vagal stimulation produced similar effects in the seven dogs without myocardial infarction. These data demonstrate that the vagal-sympathetic "accentuated antagonism" described in anesthetized animals is also present in conscious dogs
[Baroceptive reflex sensibility in non-anesthetized animals. Evaluation and comparison of 2 methods applicable to humans].
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