Autonomic blockade: assessment of the intrinsic heart rate in a closed-chest experimental porcine model

2012 ◽  
Vol 29 ◽  
pp. 74 ◽  
Author(s):  
R. Sevilla ◽  
B. Del Blanco ◽  
J. Almendral ◽  
M. Zaballos
Keyword(s):  
Heart Rate ◽  
Porcine Model ◽  
Closed Chest ◽  
Intrinsic Heart Rate ◽  
Autonomic Blockade

P4423Extreme bradycardia in athletes is due to intrinsic changes within the heart

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
M D Flannery ◽  
F Sully ◽  
K Janssens ◽  
G Morris ◽  
J Kalman ◽  
...  
Keyword(s):  
Heart Rate ◽  
Vagal Tone ◽  
Endurance Athletes ◽  
Valsalva Manoeuvre ◽  
Resting Heart Rate ◽  
Maximum Heart Rate ◽  
Vo2 Max ◽  
Heart Rates ◽  
Intrinsic Heart Rate ◽  
Autonomic Blockade

Abstract Background It is well known that athletes and in particular endurance athletes have lower resting heart rates than non-athletes. This has generally been considered a healthy adaptation. Traditionally this was thought be due to increased vagal tone. Several studies have shown that endurance athletes continue to have lower heart rates in the absence of autonomic influence suggesting bradycardia is due to intrinsic changes within the heart. A subset of endurance athletes have very low heart rates with Tour de France cyclists having described heart rates in the 30s. It is unclear whether in these elite athletes with very low heart rates the profound bradycardia is due to autonomic influence or intrinsic changes within the heart. Aim The aim of this study was to determine if extreme bradycardia in athletes is due to excess vagal tone or more profound intrinsic changes within the heart. Methods We recruited three cohorts for this study: non-athlete controls (NA), endurance athletes with a documented resting heart rate >40 (EA) and endurance athletes with a resting heart rate <40 (BA). All participants underwent baseline testing including ECG, echocardiography and VO2 max testing. All participants came back on a second occasion for treatment with dual autonomic blockade (DAB) to determine intrinsic heart rate in the following manner. After resting supine for five minutes resting heart rate was measured. Participants were then administered 0.04mg/kg of intravenous atropine. After five minutes participants were then administered 0.05mg/kg of intravenous metoprolol. This was repeated every five minutes until there was no further drop in heart rate or 0.2mg/kg had been administered. The resting heart rate at this stage was recorded as the intrinsic heart rate. Parasympathetic blockade was confirmed by lack of response to Valsalva manoeuvre and sympathetic blockade was confirmed by lack of response to metoprolol. VO2 max testing was then performed to determine maximum heart rate. Results 9 NA (7 male), 10 EA (8 male) and 5 BA (4 male) participated in this study. The average age was similar in all groups (NA 32.9y, EA 32.4y, BA 31.4y). The average resting heart rate was 71.7 in the NA group, 48.3 in the EA group and 41.6 in the BA group (p<0.05 for comparisons between all three groups). Following dual autonomic blockade resting heart rate was 86.0 in the NA group, 76.9 in the EA group and 64.4 in the BA group (p<0.05 for comparisons between all three groups). Maximum heart rate under DAB was 140.1 in the NA group, 138.0 in the EA group and 140.4 in the BA group. These differences were not significant. Conclusion In athletes with very low heart rates, bradycardia is due to more profound intrinsic changes within the heart. Acknowledgement/Funding NHMRC Project Grant

Intrinsic heart rate in the dog determined by pharmacologic denervation

1983 ◽  
Vol 245 (4) ◽  
pp. H592-H597 ◽  
Author(s):  
J. R. Brunsting ◽  
H. A. Schuil ◽  
W. G. Zijlstra
Keyword(s):  
Heart Rate ◽  
Blood Gases ◽  
Conscious Dogs ◽  
Interindividual Variation ◽  
Adrenergic Blockade ◽  
Intrinsic Heart Rate ◽  
Parasympathetic System ◽  
Autonomic Blockade ◽  
Cervical Vagotomy ◽  
The Difference

Intrinsic heart rate was measured in 19 dogs in 76 experiments after autonomic blockade, using various forms of anesthesia. Measurements were made in conscious dogs (n = 16) and in dogs in neuroleptanesthesia (n = 54) or under pentobarbital sodium (n = 6). Temperature, arterial pH, and blood gases were kept within narrow limits. Adrenergic blockade was achieved by phenoxybenzamine (2 mg X kg-1) and propranolol (2 mg X kg-1, followed by 2 mg X kg-1 X h-1). The parasympathetic system was blocked either by atropine (0.5 mg X kg-1, followed by 0.5 mg X kg-1 X h-1) and hexamethonium (20 mg X kg-1, followed by 10 mg X kg-1 X h-1) or by atropine and bilateral cervical vagotomy. Administration of hexamethonium or vagotomy was needed to block the vagal cardioacceleration unmasked by the administration of muscarinic blocking agents in conscious dogs and in dogs in neuroleptanesthesia. The mean denervated heart rate was 142.8 beats/min. This value is higher than that reported for surgically denervated hearts, the difference very likely reflecting the activity of the intact parasympathetic intrinsic cardiac innervation in surgical preparations. The estimated intraindividual and interindividual SD were 9.7 and 19.4 beats/min, respectively. The highly significant interindividual variation (P less than 0.01) contradicts the concept of an intrinsic heart rate as a practically constant species-dependent quantity.

Selective autonomic blockade of conditioned and unconditioned heart rate changes in rabbits

1974 ◽  
Vol 2 (4) ◽  
pp. 493-501 ◽  
Author(s):  
Alice Fredericks ◽  
John W. Moore ◽  
Frederick U. Metcalf ◽  
James S. Schwaber ◽  
Neil Schneiderman
Keyword(s):  
Heart Rate ◽  
Autonomic Blockade

Influence of cardiac innervation on intrinsic heart rate in dogs

1990 ◽  
Vol 258 (4) ◽  
pp. H1132-H1137 ◽  
Author(s):  
J. M. Evans ◽  
D. C. Randall ◽  
J. N. Funk ◽  
C. F. Knapp
Keyword(s):  
Heart Rate ◽  
Intrinsic Rate ◽  
Conscious State ◽  
Autonomic Innervation ◽  
Autonomic Activity ◽  
Cardiac Innervation ◽  
Cardiac Denervation ◽  
Ganglionic Blockade ◽  
Intrinsic Heart Rate

Intrinsic heart rate is defined as the rate at which the heart beats when all cardiac neural and hormonal inputs are removed. We determined the effect of prevailing autonomic innervation of the heart on the intrinsic heart rate in chronically maintained, sedated, normally innervated dogs (n = 14), and in 14 other dogs that had previously (greater than 12 day) undergone complete surgical cardiac denervation. Intrinsic rate was determined in both groups using the following two procedures: 1) pharmacological effector blockade; and 2) pharmacological ganglionic blockade. The intrinsic rate determined by effector blockade was 142.9 +/- 7.2 (SE) beats/min in the dogs with intact cardiac innervation. When the same treatment was given after total surgical cardiac denervation, intrinsic rate was 97.9 +/- 4.8 beats/min. Intrinsic heart rate was significantly (P less than 0.05) lower in surgically denervated dogs. Ganglionic blockade in surgically denervated animals yielded an intrinsic rate of 90.0 +/- 8.5 beats/min, which was again significantly lower than the corresponding value of 128.4 +/- 5.5 beats/min in normal dogs. There was no difference in the intrinsic heart rate as determined by effector vs. ganglionic blockade in either group of dogs. An additional six dogs were subjected to selective surgical sinoatrial nodal parasympathectomy; their intrinsic rate (effector blockade) in the conscious state was 115.8 +/- 4.3 beats/min; this was significantly lower than the corresponding value for normal dogs and significantly greater than in dogs subject to total surgical cardiac denervation. The lower rate observed in the totally denervated and selectively denervated dogs after effector and/or ganglionic blockades implies that intrinsic heart rate depends on the level or nature of prevailing autonomic activity.

Baroreflex modulation of heart rate and initiation of atrial activation in dogs

1988 ◽  
Vol 255 (3) ◽  
pp. H503-H513 ◽  
Author(s):  
R. B. Schuessler ◽  
T. E. Canavan ◽  
J. P. Boineau ◽  
J. L. Cox
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Right Atrial ◽  
Autonomic Blockade ◽  
Left And Right ◽  
Atrial Activation ◽  
The Right ◽  
A Site ◽  
Induced Changes ◽  
Cardiac Nerves

In open-chest dogs, blood pressure was regulated by titrating doses of phenylephrine and nitroprusside to determine its effect on heart rate and pacemaker location. Changes in blood pressure correlated with changes in heart rate (r = 0.86). Activation time mapping demonstrated multicentric atrial activation, with a site of origin-rate relationship. The fastest pacemakers were located in the most cranial regions and slowest in the most caudal areas. In this chloralose-morphine anesthetized model, autonomic blockade with atropine and propranolol suggests that acute baroreflex-induced changes in heart rate were mediated exclusively by either increased sympathetic or parasympathetic tone and were not associated with inhibition of the opposite system. Division of right and left thoracic cardiac nerves indicated the left sympathetics participated in the baroreflex in 50% of the animals and the left parasympathetics in 90% of the animals. Both the right sympathetics and parasympathetics were active in the baroreflex in all animals. The data demonstrate that physiological heart rate response is regulated through an extensive system of right atrial pacemakers modulated by both left and right efferent cardiac nerves.

Effect of radiofrequency catheter ablation of accessory pathways on autonomic tone in children

1999 ◽  
Vol 9 (4) ◽  
pp. 377-383 ◽  
Author(s):  
Ruchir Sehra ◽  
Joyce E. Hubbard ◽  
Susan P. Straka ◽  
Naomi S. Fineberg ◽  
Douglas P. Zipes ◽  
...  
Keyword(s):  
Heart Rate ◽  
Catheter Ablation ◽  
Supraventricular Tachycardia ◽  
Radiofrequency Catheter Ablation ◽  
Autonomic Function ◽  
Accessory Pathways ◽  
Non Invasive ◽  
Autonomic Changes ◽  
Before And After ◽  
Autonomic Blockade

AbstractBackgroundRadiofrequency catheter ablation is standard treatment for children with re-entrant supraventricular tachycardias. Autonomic changes have been noted after such ablation for atrioventricular nodal re-entry tachycardia, but not as well documented with atrioventricular re-entry over an accessory pathway.Methods and resultsIn 10 normal paediatric volunteers and 12 children referred for electrophysiologic testing and radiofrequency ablation of supraventricular tachycardia, non-invasive autonomic function tests and tilt-table testing were performed, and the variability in 24-h heart rate was analysed. Patients with supraventricular tachycardia underwent these tests both 24–72 h before and 24 h after ablation. Patients with tachycardia underwent additional autonomic testing to assess the sensitivity of baroreceptors and the intrinsic heart rate with autonomic blockade immediately before and after ablation. One non-invasive autonomic function test, namely handgrip, demonstrated significant differences (p < 0.05) in diastolic blood pressure before and after ablation, though these values did not differ from controls. Significant decreases were noted in two indexes of the variability of heart rate before and after ablation (p < 0.05). Certain tilt test variables also demonstrated significant differences between controls and those with tachycardia subsequent to ablation. Intracardiac testing demonstrated changes (p < 0.05) in sinus cycle lengths, effective refractory periods and/or blood pressures at baseline and during testing of the sensitivity of baroreceptors before and after ablation. These changes were consistent with increased sympathetic or decreased parasympathetic tone. With autonomic blockade, these differences were abolished.ConclusionsCatheter ablation of accessory pathways in children was associated with changes consistent with increased sympathetic or decreased parasympathetic tone. These autonomic changes persisted 24 h after the ablation procedure.

Hypotension in Fetal and Newborn Lambs; Different Patterns of Reflex Heart Rate Control Revealed by Autonomic Blockade

Neonatology ◽  
1983 ◽  
Vol 44 (6) ◽  
pp. 358-365 ◽  
Author(s):  
Adrian M. Walker ◽  
J.P. Cannata ◽  
B.C. Ritchie ◽  
J.E. Maloney
Keyword(s):  
Heart Rate ◽  
Rate Control ◽  
Heart Rate Control ◽  
Autonomic Blockade
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