Hierarchy of ventricular pacemakers.

Hope, Ronald R.; Scherlag, Benjamin J.; El‐Sherif, Nabil; Lazzara, Ralph

doi:10.1161/01.res.39.6.883

Cited by 26 publications

(4 citation statements)

References 28 publications

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“…The control automatic rates (mean ± SD; impulses/min) for these fibers were 17.4 ± 9.5 (adult) and 16.2 ± 7.8 (neonate) (p > 0.5). These rates did not differ significantly from those reported previously by us [1] and by others [14] in studies of the distal ventricular specialized con- ducting system. 8 adult (25%) and 11 (48%) neonatal fibers showed an increase in rate when superfused with phenylephrine, 5 X 10-8 M. For these fibers the control rates were 9.0 ± 6.4 (adult) and 9.5 ± 7.5 (neonate) impulses/min (p > 0.05).…”

Section: Studies Of Tissue Catecholamine Contentsupporting

confidence: 51%

Developmental Changes in Alpha Adrenergic Effects on Canine Purkinje Fiber Automaticity

Reder¹,

Danilo²,

Rosen³

1984

Dev Pharmacol Ther

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Canine cardiac Purkinje fiber automaticity is modified by adrenergic agonists. Alpha adrenergic agonists slow and beta agonists increase the rate of automatic discharge. These effects vary with maturation and development. We used standard microelectrode techniques to study the effects of the alpha agonist, phenylephrine, on automaticity in isolated neonatal (< 10 days) and adult canine cardiac Purkinje fibers. Fibers were superfused with 5 X 10^-8 M phenylephrine dissolved in Tyrode’s solution. 75% (24/32) of adult and 52% (12/23) of neonatal fibers showed a decrease in rate. The magnitude of the decrease was similar at both ages and the effect was blocked during superfusion with 1 X 10^-9 M phentolamine. The remaining adult and neonatal fibers demonstrated a significant increase in rate in response to 5 X 10^-8 M phenylephrine. This effect was blocked by 5 X 10^-7 M propranolol in the adult group but not in the neonates. However, the increase in rate of fibers from 0- to 2-day neonates was blocked by phentolamine. As an indicator of adrenergic innervation of neonatal hearts, we assayed the myocardial norepinephrine concentration. There was a 6- to 8-fold increase in concentration during the first 10 days of neonatal life, suggesting that innervation was rapidly increasing during this time. In summary, neonatal Purkinje fibers can show an alpha adrenergic- induced acceleration of automatic rate. This alpha adrenergic acceleration is not seen in adults. The change in response from neonate to adult may be effected by growth and development of autonomic nerves and associated changes in receptor function.

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Section: Studies Of Tissue Catecholamine Contentsupporting

confidence: 51%

Developmental Changes in Alpha Adrenergic Effects on Canine Purkinje Fiber Automaticity

Reder¹,

Danilo²,

Rosen³

1984

Dev Pharmacol Ther

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“…Whereas a sinus rhythm can be around 130 bpm in dogs, a ventricular escape rhythm will most likely be significantly lower than that in healthy dogs, being as low as 40 bpm. (Hope et al 1976). The other situation in which a ventricular beat is responsible for the cardiac output is when a ventricular complex happens before the next R wave is supposed to and is called a ventricular premature complex (VPC), but in this case it occurs early, compared to the underlying rhythm and usually has a faster rhythm.…”

Section: Escape Beatsmentioning

confidence: 99%

Use of intravenous lidocaine to treat dexmedetomidine-induced bradycardia in sedated and anesthetized dogs

Tisotti

Valverde

Hopkins

et al. 2021

Veterinary Anaesthesia and Analgesia

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This thesis evaluated the use of intravenous lidocaine to treat the bradycardia associated with the administration of the sedative dexmedetomidine in canine anesthetic protocols. Research Beagle dogs were assigned to three different groups in a randomized crossover design that involved the administration of intravenous dexmedetomidine in different modalities of the anesthetic protocol. In two groups, dexmedetomidine was administered to dogs while awake and in the third group while anesthetized with isoflurane.After receiving dexmedetomidine, dogs were given intravenous lidocaine as a bolus 30 minutes later, followed by a second bolus and a constant rate infusion 20 minutes after the first bolus, in one of the awake groups and the anesthetized group. The other awake group received the lidocaine bolus and constant rate infusion 5 minutes after the dexmedetomidine.Intravenous lidocaine increased heart rate in awake and anesthetized dogs pretreated with intravenous dexmedetomidine. Additional benefits from lidocaine administration included an increase in cardiac index and a decrease in systemic vascular resistance.iii DEDICATIONIn Memoriam of my grandparents Ieda Hainzenreder and João de Mesquita.Foremost, I would like to thank my supervisor, Dr. Alexander Valverde, for opening the doors for me, for being resolute, tireless and for his guidance during my program. I would also like to thank all the anesthesia faculties I had the opportunity to work with and absorb some of their knowledge, but specially to Drs. Andrea Sanchez, Carolyn Kerr and Melissa Sinclair for the personal and professional support along these three years.

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“…(1] The epicardial hreakthroughs of these tachycardias occurred most frequently in the region of the RVOT (Figs. [4][5][6][8][9][10]. This occurred despite the fact that the Purkinje fiher network does not extend into the RVOT.^« (2] The areas encompassed hy the hreakthroughs were relatively small.…”

Section: Discussionmentioning

confidence: 99%

Distinct Activation Patterns of Idioventricular Rhythms and Sympathetically‐Induced Ventricular Tachycardias in Dogs with Atrioventricular Block

Cardinal

Scherlag

Vermeulen

et al. 1992

Pacing Clinical Electrophis

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To investigate mechanisms of ventricular impulse formation in response to sympathetic stimulation in the healthy canine heart in situ, we compared the patterns of ventricular activation during the idioventricular rhythms arising after complete atrioventricular (AV) block and ventricular tachycardias induced by RSG or LSG stimulation. Isochronal maps were generated by computer from 116-127 unipolar electrograms recorded from the entire ventricular epicardium in 15 open chest, anesthetized dogs. In eight of these, bipolar electrograms were recorded with plunge electrodes from 11 selected endocardial sites located below epicardial breakthrough areas. Intracardiac recordings from the His-Purkinje system were made with electrode catheters. After electrograms were recorded during sinus rhythm, complete AV block was induced by injecting formaldehyde into the AV node and idioventricular rhythms occurred spontaneously at a rate of 37 +/- 12 beats/min (mean +/- SD, n = 25). During idioventricular rhythms, endocardial activation preceded the earliest epicardial breakthrough, which occurred in either the right anterior paraseptal region, antero-apical left ventricle, or postero-apical left ventricle. These sites were consistent with a focal origin in the subendocardial His-Purkinje system. Total epicardial activation times lasted for 47 +/- 13 msec (n = 40). Idioventricular rhythms were suppressed by overdrive pacing (intermittent trains of ten beats with decremental cycle length from 500 to 200 msec) or by intravenous calcium infusion (to plasma levels of 10.1-15.2 mM). Right or left stellate ganglion stimulation increased idioventricular rhythm rates (to 52 +/- 13 beats/min, n = 28) and also induced, in all preparations, ventricular tachycardias that had significantly faster rates (189 +/- 55 beats/min, n = 27, P less than 0.005). Ventricular fibrillation was induced after brief runs of ventricular tachycardia in five of the preparations. During ventricular tachycardias, epicardial activation occurred on the right ventricular outflow tract or the postero-lateral wall of the left ventricle, and preceded endocardial activation in 50% of cases. Total epicardial activation times (103 +/- 29 beats/min) were significantly longer than during idioventricular rhythms (P less than 0.005). Ventricular tachycardias displayed overdrive excitation at critical pacing cycle lengths (360-280 msec) and were not suppressed by calcium infusion. Thus, differential mechanisms of impulse formation with distinct localizations can be elicited from healthy ventricular myocardium.

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Hierarchy of ventricular pacemakers.

Cited by 26 publications

References 28 publications

Developmental Changes in Alpha Adrenergic Effects on Canine Purkinje Fiber Automaticity

Developmental Changes in Alpha Adrenergic Effects on Canine Purkinje Fiber Automaticity

Use of intravenous lidocaine to treat dexmedetomidine-induced bradycardia in sedated and anesthetized dogs

Distinct Activation Patterns of Idioventricular Rhythms and Sympathetically‐Induced Ventricular Tachycardias in Dogs with Atrioventricular Block

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