Electrocardiogram of the Crocodilian Heart

Davies, Francis; Francis, E. T. B.; King, Tiffany

doi:10.1038/167146a0

Cited by 12 publications

(4 citation statements)

References 1 publication

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“…Given that the initial handling involved noosing and physically extracting the alligator from its pond, it is likely that this interaction caused the alligator's heart rate to increase by at least 2.5× over the resting rate. Heart rates in the range of 38.5 bpm have been reported from previous studies on crocodilians (e.g., Buchanan, 1909;Davies et al, 1951;Huggins et al, 1969). The stress evoked during this handling not only produced significant tachycardia, but this elevated heart rate was of long duration.…”

supporting

confidence: 69%

Cardiac response to stimulation and stress in the American alligator (Alligator mississippiensis)

et al. 2020

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Previous descriptions of the direction (tachycardia versus bradycardia), magnitude, and duration of the cardiac stimulation/stress response of the American alligator (Alligator mississippiensis) have been contradictory. Superficial EKG leads were used to quantify heart rate while presenting a graded series of stimuli to a cohort of 5 sub-adult alligators. Only tachycardic responses were recorded. Stress (manual restraint and transport) induced a nearly 3-fold increase over the resting heart rate (∼17 bpm), which decreased only 7 bpm over 40 minutes in a stimulus-free environment. Lower-level stimulation (i.e., exposure to room light) produced a significantly smaller response than did higher-level stimulation (i.e., physical contact), both responses were transitory, lasting approximately 120 s.

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supporting

confidence: 69%

Cardiac response to stimulation and stress in the American alligator (Alligator mississippiensis)

et al. 2020

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“…Indeed, the QRS duration, a functional measure for Purkinje system, was substantially longer in alligators than in comparatively sized mammals, even when heated to mammalian body temperatures. In other crocodilians, the QRS duration is also approximately 100 ms suggesting that the speed of ventricular activation is similar across crocodilians ( Christian and Grigg, 1999 ; Davies et al, 1951 ; Heaton-Jones and King, 1994 ; Syme et al, 2002 ; Wang et al, 1991 ). It further suggests that the specialized atrioventricular conduction pathway does not have an appreciable effect on ventricular activation time.…”

Section: Discussionmentioning

confidence: 99%

“…Among ectotherms, only crocodilians (alligators, crocodiles, and gharials) have a full ventricular septum and the electrical activation of the ventricle of the freshwater crocodile has been reported to propagate differently from that of other reptiles ( Jensen et al, 2012 ; Christian and Grigg, 1999 ). Early anatomical works suggested that atrioventricular canal myocardium of the American alligator projects onto the ventricular septum ( Greil, 1903 ; Swett, 1923 ), but there was no mention of bundle branches and the later investigators that unequivocally show the specialized conduction system in mammals and birds ( Davies and Francis, 1946 ), could not find specialized tissues in crocodilians ( Davies et al, 1952 ; Davies et al, 1951 ). Here, we investigated the ventricles of the American alligator for the presence of atrioventricular conduction system components to address the question of their origin.…”

Section: Introductionmentioning

confidence: 99%

Specialized impulse conduction pathway in the alligator heart

Jensen

Boukens

Crossley

et al. 2018

eLife

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Mammals and birds have a specialized cardiac atrioventricular conduction system enabling rapid activation of both ventricles. This system may have evolved together with high heart rates to support their endothermic state (warm-bloodedness) and is seemingly lacking in ectothermic vertebrates from which first mammals then birds independently evolved. Here, we studied the conduction system in crocodiles (Alligator mississippiensis), the only ectothermic vertebrates with a full ventricular septum. We identified homologues of mammalian conduction system markers (Tbx3-Tbx5, Scn5a, Gja5, Nppa-Nppb) and show the presence of a functional atrioventricular bundle. The ventricular Purkinje network, however, was absent and slow ventricular conduction relied on trabecular myocardium, as it does in other ectothermic vertebrates. We propose the evolution of the atrioventricular bundle followed full ventricular septum formation prior to the development of high heart rates and endothermy. In contrast, the evolution of the ventricular Purkinje network is strongly associated with high heart rates and endothermy.

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“…However, our observations suggest that the type of QRS response is related to phylogenetic differ ences in the conducting system of the heart [11]: cell-to-cell in poikilo therms [3] and specialized conducting tissue in honieotherms [16], To test this hypothesis, two experimental preparations were designed to allow in the same mammalian heart both specialized conduction and ceil-to-cell conduction: (A) a cat heart with a normal conducting system on one side and an interrupted system (bundle branch block. BBB) on the other, and (B) a normal cat heart displaying either normal sinus rhythm propagated by the bundle or artificial ventricular pacing induced by an external pace maker and propagated through the heart muscle.…”

mentioning

confidence: 99%

Role of the Cardiac Conduction System in Determining the QRS Amplitude after Bleeding

Manoach¹,

Grosman²,

Varon³

et al. 1974

Cardiology

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The QRS complex in the ECG of poikilotherms is increased by bleeding. The opposite reaction is observed in homeotherms. In previous studies, the type of QRS response to hemorrhage and infusion was ascribed to a phylogenetic difference, namely the presence or absence of a specialized conduction system in the heart. In order to substantiate the role of the specialized conducting system, two mammalian preparations were designed using the same species (cat) under conditions allowing both specialized conduction and cell-to-cell conduction. Comparison of the changes observed during bleeding or transfusion in the R’ wave of cats with bundle branch block, and in the depolarization wave obtained by ventricular pacing (both of which mimic poikilotherm conduction), with the changes in the R wave in normal cats, clearly show the dependence of the changes in QRS amplitude on the type of conduction system in the heart.

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Electrocardiogram of the Crocodilian Heart

Cited by 12 publications

References 1 publication

Cardiac response to stimulation and stress in the American alligator (Alligator mississippiensis)

Cardiac response to stimulation and stress in the American alligator (Alligator mississippiensis)

Specialized impulse conduction pathway in the alligator heart

Role of the Cardiac Conduction System in Determining the QRS Amplitude after Bleeding

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