Electrophysiology in horses involves the study of the electrical properties and activities of equine tissues, particularly the heart and nervous system. This field encompasses the measurement and analysis of electrical signals to assess the function and health of these systems. In equine cardiology, electrophysiological studies are utilized to evaluate cardiac rhythm, detect arrhythmias, and guide therapeutic interventions. In the context of the nervous system, electrophysiological techniques can help in diagnosing neurological disorders and assessing nerve function. This page compiles peer-reviewed research studies and scholarly articles that explore the methodologies, applications, and clinical relevance of electrophysiology in the assessment and management of equine health.
Hesselkilde EM, Isaksen JL, Petersen BV, Carstensen H, Jespersen T, Pehrson S, Kanters JK, Buhl R.In equine medicine, 12-lead electrocardiograms (ECGs) rarely are used, which may in part be a result of shortcomings in the existing guidelines for obtaining 12-lead ECGs in horses. The guidelines recommend placing the limb leads on the extremities, which is inappropriate because the ventricular mean electrical axis is then perpendicular to the limb leads, leading to large variations in ECG configuration even among healthy horses. From an electrophysiological point of view, the leads instead should be parallel to the electrical axis to minimize variability. Objective: Develop an improved metho...
van Loon G, Van Steenkiste G, Vera L, Decloedt A.Minimally-invasive catheter-based interventional cardiology is a mainstay for the diagnosis and treatment of arrhythmias in human medicine. Very accurate imaging using fluoroscopy, CT and MRI is essential during interventional cardiology procedures. Because these imaging techniques are either not possible or provide too little anatomical detail in horses, echocardiography is currently the best technique to visualize catheters in horses. Over the past decades, catheter-based techniques have been applied to induce arrhythmias using pacing and to perform arrhythmia research using electrophysiolog...
Van Steenkiste G, L V, Decloedt A, Schauvliege S, Boussy T, van Loon G.Understanding the depolarisation pattern of the equine heart under normal physiologic conditions, and its relationship to the surface electrocardiogram (ECG), is of uppermost importance before any further research can be done about the pathophysiology of complex arrhythmias. In the present study, a 3D electro-anatomical mapping system was used to evaluate the qualitative and quantitative depolarisation patterns and correlation to the surface ECG of both the atrial and ventricular endocardium in seven healthy horses in sinus rhythm under general anaesthesia. Bipolar activation maps of the endoc...
Van Steenkiste G, De Clercq D, Boussy T, Vera L, Schauvliege S, Decloedt A, van Loon G.Ultra-high-density cardiac mapping allows very accurate characterisation of atrial and ventricular electrophysiology and activation timing. Objective: To describe the technique and evaluate the feasibility of magnetic electro-anatomical mapping of the equine heart. Methods: In vivo experimental method development. Methods: A mapping system using an 8.5F bidirectional deflectable catheter with a deployable mini-basket (3-22 mm) containing 64 electrodes divided over eight splines was evaluated. Based upon predefined beat acceptance criteria, the system automatically acquires endocardial electro...
Kikuchi K, Kozai K, Hojo T, Sakatani M, Okuda K, Bai H, Kawahara M, Takahashi M.We investigated the electrical impedance of the reproductive tracts (vagina and uterine endometrial tissues) and the expression of mucus-related genes to identify the stage of the estrous cycle in mares. We first examined vaginal impedance in native Hokkaido mares during their estrous cycle and found no significant differences. However, impedance levels tended to decrease towards ovulation. Furthermore, we investigated the estrous cycle by measuring the electrical impedance of the uterine endometrial tissues obtained from carcasses of mares. We found that impedance levels in the endometrial ti...
Haugaard MM, Pehrson S, Carstensen H, Flethøj M, Hesselkilde EZ, Praestegaard KF, Diness JG, Grunnet M, Jespersen T, Buhl R.Only few pharmacologic compounds have been validated for treatment of atrial fibrillation (AF) in horses. Studies investigating the utility and safety of flecainide to treat AF in horses have produced conflicting results, and the antiarrhythmic mechanisms of flecainide are not fully understood. Objective: To study the potential of flecainide to terminate acutely induced AF of short duration (≥ 15 minutes), to examine flecainide-induced changes in AF duration and AF vulnerability, and to investigate the in vivo effects of flecainide on right atrial effective refractory period, AF cycle length...
Baldacchino F, Cadier J, Porciani A, Buatois B, Dormont L, Jay-Robert P.Urine volatiles from different ungulates (cows, horses and sheep) were tested as bait for tabanids in southeastern France using Nzi traps during the early summer of 2011. Tabanus bromius Linnaeus, 1758 and Atylotus quadrifarius (Loew, 1874) (both: Diptera: Tabanidae) were the most captured species, respectively representing 57% and 41% of all tabanids collected (all of which were female). Horse urine significantly increased catches of T. bromius (1.6-fold) and A. quadrifarius (3.5-fold), and sheep urine significantly increased catches of A. quadrifarius (2.5-fold). In parallel, an electroanten...
De Clercq D, van Loon G, Tavernier R, Duchateau L, Deprez P.In humans, atrial fibrillation (AF) induces electrical, contractile, and structural remodeling leading to AF stabilization. Little is known about AF-induced atrial remodeling in horses. Objective: Induced AF produces rapid atrial electrical and contractile remodeling in horses. Methods: Six horses, 5 animals completed the study. Methods: Each horse was instrumented with a pulse generator and pacemaker to maintain AF by burst pacing and to study atrial and ventricular electrophysiology (AF cycle length [AFCL], AF duration, and atrial/ventricular effective refractory period [AERP/VERP] at differ...
McGurrin MK, Physick-Sheard PW, Kenney DG.Transvenous electrical cardioversion (TVEC) has been developed for treatment of atrial fibrillation (AF) in horses. The relationship among patient variables, treatment response, and outcome in a typical referral population has not been evaluated. Objective: Patient variables such as age, sex, weight, and duration of arrhythmia affect prognosis for response to treatment and the energy level at which cardioversion occurs. Methods: TVEC was applied to 72 episodes of lone AF in 63 client-owned performance horses, with the majority (54) being Standardbred racehorses. Methods: Catheterization of the...
Kozelek P, Holcik J, Sedlinska M.The paper describes experiments and their results that offered an insight to relationship between RR and QT intervals in equine ECG signals recorded under various conditions. In contrast to human heart in a great number of cases the QT intervals prolonged with a heart rate acceleration. Peak-to-peak differences between maximum and minimum RR intervals during the excitation response in non-standard responses were twice as smaller as in standard responses and the lengths of QT intervals were significantly longer in the non-standard records. This fact means that the electrical processes in equine...
Schwarzwald CC, Hamlin RL, Bonagura JD, Nishijima Y, Meadows C, Carnes CA.Although atrial arrhythmias are clinically important in horses, atrial electrophysiology has been incompletely studied. Objective: Standard electrophysiologic methods can be used to study drug effects in horses. Specifically, the effects of diltiazem on atrioventricular (AV) nodal conduction are rate-dependent and allow control of ventricular response rate during rapid atrial pacing in horses undergoing quinidine treatment. Methods: Fourteen healthy horses. Methods: Arterial blood pressure, surface electrocardiogram, and right atrial electrogram were recorded during sinus rhythm and during pro...
Mobasheri A, Gent TC, Nash AI, Womack MD, Moskaluk CA, Barrett-Jolley R.Chondrocytes are highly sensitive to variations in extracellular glucose and oxygen levels in the extracellular matrix. As such, they must possess a number of mechanisms to detect and respond to alterations in the metabolic state of cartilage. In other organs such as the pancreas, heart and brain, such detection is partly mediated by a family of potassium channels known as K(ATP) (adenosine 5'-triphosphate-sensitive potassium) channels. Here we investigate whether chondrocytes too express functional K(ATP) channels, which might, potentially, serve to couple metabolic state with cell activity. ...
Hudson NP, Mayhew IG, Pearson GT.Intracellular microelectrode recordings were made from smooth muscle cells in cross-sectional preparations of equine ileum, superfused in vitro. Membrane potential oscillations and spike potentials were recorded in all preparations, but recordings were made more readily from cells in the longitudinal muscle layer than from cells in the circular layer. The mean (se) resting membrane potential (RMP) of smooth muscle cells in the longitudinal muscle layer was -51.9 (1.2) mV, and the membrane potential oscillations in this layer had a mean amplitude of 4.8 (0.4) mV, a frequency of 9.0 (0.1) cycles...
Rakestraw PC, Snyder JR, Sanders KM, Shuttleworth WC.To evaluate electrical activity of jejunal circular muscle in horses and characterize electrical responses to stimulation by intrinsic inhibitory neurons. Methods: Portions of jejunum obtained from horses euthanatized for reasons other than gastrointestinal tract disease. Methods: Isolated circular muscle preparations were perfused with oxygenated modified Krebs solution. Glass microelectrodes were used for intracellular recording of membrane potentials from single smooth muscle cells. Electrical activity and responses to electrical field stimulation (EFS) of intrinsic neurons in the presence ...
Yamaya Y, Kubo K, Amada A, Sato K.The atrioventricular (AV) conductive functions were investigated before and after the pharmacological autonomic nervous blockade (PAB) through the electrophysiological study on six horses (AV block group) in which the dropped beats occurred more frequently (over 200 beats/24 hr) and on five horses (control group) in which the dropped beats occurred sporadically (under 200 beats/24 hr) or in which the arrhythmias were not recognized at all on the long-term electrocardiogram. As a result, AV conductivity, conduction time and refractoriness in the AV block group were lower, longer and higher, res...
von Engelhardt W, Rösel E, Rechkemmer G.Short circuit current (ISC) and transepithelial conductance (gt) across sheets of epithelia were measured in the caecum, the proximal and the distal colon of pig, sheep, pony, rat and guinea pig. The electrical parameters underline the basic segmental and species differences. The diversity of ISC demonstrates the different nature of electrogenic transport mechanisms, and data clearly show the heterogeneity with respect to transport mechanisms along the large intestine in the various species. The great differences in amiloride sensitive ISC indicate the variabilities in the electrogenic Na tran...
Strain GM, Taylor DS, Graham MC, Kamerling SG.Cortical somatosensory-evoked potentials (SEP) were recorded from thoracic and pelvic limbs in 15 horses (13 Thoroughbreds and 2 Quarter Horses). Ulnar nerve SEP were evoked by electrical stimulation of the lateral palmar branch of the ulnar nerve at the level of the metacarpophalangeal joint. Recordings were taken between electrodes at 2 cm lateral to the vertex (contralateral to the stimulated limb) and the midpoint of the interorbital line. Four peaks were found in all recordings: N1, P1, N2, and P2. Latencies to the peaks were 39.0 +/- 2.7, 45.5 +/- 5.3, 50.4 +/- 5.2, and 62.3 +/- 3.7 ms (...
Miller PJ, Holmes JR.Beat-to-beat variation in the amplitude of the QRS waveform from 13 horses with second degree partial atrioventricular block was examined using an orthogonal lead (X,Y,Z) system. The peak positive deflections (XR, YR and ZR) and peak negative deflections (XQS, YS and ZQ) were regressed against PR and RR intervals. XQS was used to indicate that the peak negative deflection in X could have been a Q or S wave. XR and YR were directly related to PR (P less than 0.001) and XQS and YS were inversely related to PR (P less than 0.001). YR was also directly related to RR (P less than 0.001) but not so ...
Geddes LA, Bourland JD, Tacker WA.The threshold energy and current required for ventricular defibrillation was determined in dogs ranging in weight from 6.4 to 38 kg and in ponies ranging in weight from 40 to 101 kg. Trapezoidal waves, 10 ms in duration, with 10%, 50%, 70%, and 90% tilt were applied to transchest electrodes. For all values of tilt, the energy and current required increased with body weight. The energy dose (joules per kilogram of body weight) was higher for the heavier animals, whereas the current dose (peak amperes per kilogram of body weight) was essentially the same for dogs and ponies. In both species and ...
Holmes JR.The paper describes the spatial vector changes during ventricular depolarisation in 190 horses using a semi-orthogonal ECG lead system. The replacement of planar vector loops by a plot of 3 parameters to depict the changing spatial vector, with a time base on the X axis, is described and illustrated. Some horses with diastolic murmurs and some with a history of respiratory problems formed 2 distinct groups. As a result of these findings a possible relationship between the vector changes and the anatomical siting of the ventricles is suggested and discussed. Attention is drawn to certain measur...
Darke PG, Holmes JR.The paper describes the distribution of cardiac potentials on the body surface of four horses. Potentials were recorded at 200 to 300 equallyspaced sites synchronously with a reference lead; they were measured at 10 msec. instants of time, and were plotted on diagrams. While some evidence of multiple dipolar activity occurred during each part of the cardiac cycle, the majority of potentials arose as if from a single resultant dipole.
De Clercq D, van Loon G, Tavernier R, Duchateau L, Deprez P.In humans, atrial fibrillation (AF) induces electrical, contractile, and structural remodeling leading to AF stabilization. Little is known about AF-induced atrial remodeling in horses. Objective: Induced AF produces rapid atrial electrical and contractile remodeling in horses. Methods: Six horses, 5 animals completed the study. Methods: Each horse was instrumented with a pulse generator and pacemaker to maintain AF by burst pacing and to study atrial and ventricular electrophysiology (AF cycle length [AFCL], AF duration, and atrial/ventricular effective refractory period [AERP/VERP] at differ...
McGurrin MK, Physick-Sheard PW, Kenney DG.Transvenous electrical cardioversion (TVEC) has been developed for treatment of atrial fibrillation (AF) in horses. The relationship among patient variables, treatment response, and outcome in a typical referral population has not been evaluated. Objective: Patient variables such as age, sex, weight, and duration of arrhythmia affect prognosis for response to treatment and the energy level at which cardioversion occurs. Methods: TVEC was applied to 72 episodes of lone AF in 63 client-owned performance horses, with the majority (54) being Standardbred racehorses. Methods: Catheterization of the...
Mobasheri A, Gent TC, Nash AI, Womack MD, Moskaluk CA, Barrett-Jolley R.Chondrocytes are highly sensitive to variations in extracellular glucose and oxygen levels in the extracellular matrix. As such, they must possess a number of mechanisms to detect and respond to alterations in the metabolic state of cartilage. In other organs such as the pancreas, heart and brain, such detection is partly mediated by a family of potassium channels known as K(ATP) (adenosine 5'-triphosphate-sensitive potassium) channels. Here we investigate whether chondrocytes too express functional K(ATP) channels, which might, potentially, serve to couple metabolic state with cell activity. ...
van Loon G, Van Steenkiste G, Vera L, Decloedt A.Minimally-invasive catheter-based interventional cardiology is a mainstay for the diagnosis and treatment of arrhythmias in human medicine. Very accurate imaging using fluoroscopy, CT and MRI is essential during interventional cardiology procedures. Because these imaging techniques are either not possible or provide too little anatomical detail in horses, echocardiography is currently the best technique to visualize catheters in horses. Over the past decades, catheter-based techniques have been applied to induce arrhythmias using pacing and to perform arrhythmia research using electrophysiolog...
Hesselkilde EM, Isaksen JL, Petersen BV, Carstensen H, Jespersen T, Pehrson S, Kanters JK, Buhl R.In equine medicine, 12-lead electrocardiograms (ECGs) rarely are used, which may in part be a result of shortcomings in the existing guidelines for obtaining 12-lead ECGs in horses. The guidelines recommend placing the limb leads on the extremities, which is inappropriate because the ventricular mean electrical axis is then perpendicular to the limb leads, leading to large variations in ECG configuration even among healthy horses. From an electrophysiological point of view, the leads instead should be parallel to the electrical axis to minimize variability. Objective: Develop an improved metho...
Baldacchino F, Cadier J, Porciani A, Buatois B, Dormont L, Jay-Robert P.Urine volatiles from different ungulates (cows, horses and sheep) were tested as bait for tabanids in southeastern France using Nzi traps during the early summer of 2011. Tabanus bromius Linnaeus, 1758 and Atylotus quadrifarius (Loew, 1874) (both: Diptera: Tabanidae) were the most captured species, respectively representing 57% and 41% of all tabanids collected (all of which were female). Horse urine significantly increased catches of T. bromius (1.6-fold) and A. quadrifarius (3.5-fold), and sheep urine significantly increased catches of A. quadrifarius (2.5-fold). In parallel, an electroanten...
Van Steenkiste G, L V, Decloedt A, Schauvliege S, Boussy T, van Loon G.Understanding the depolarisation pattern of the equine heart under normal physiologic conditions, and its relationship to the surface electrocardiogram (ECG), is of uppermost importance before any further research can be done about the pathophysiology of complex arrhythmias. In the present study, a 3D electro-anatomical mapping system was used to evaluate the qualitative and quantitative depolarisation patterns and correlation to the surface ECG of both the atrial and ventricular endocardium in seven healthy horses in sinus rhythm under general anaesthesia. Bipolar activation maps of the endoc...
Van Steenkiste G, De Clercq D, Boussy T, Vera L, Schauvliege S, Decloedt A, van Loon G.Ultra-high-density cardiac mapping allows very accurate characterisation of atrial and ventricular electrophysiology and activation timing. Objective: To describe the technique and evaluate the feasibility of magnetic electro-anatomical mapping of the equine heart. Methods: In vivo experimental method development. Methods: A mapping system using an 8.5F bidirectional deflectable catheter with a deployable mini-basket (3-22 mm) containing 64 electrodes divided over eight splines was evaluated. Based upon predefined beat acceptance criteria, the system automatically acquires endocardial electro...
Schwarzwald CC, Hamlin RL, Bonagura JD, Nishijima Y, Meadows C, Carnes CA.Although atrial arrhythmias are clinically important in horses, atrial electrophysiology has been incompletely studied. Objective: Standard electrophysiologic methods can be used to study drug effects in horses. Specifically, the effects of diltiazem on atrioventricular (AV) nodal conduction are rate-dependent and allow control of ventricular response rate during rapid atrial pacing in horses undergoing quinidine treatment. Methods: Fourteen healthy horses. Methods: Arterial blood pressure, surface electrocardiogram, and right atrial electrogram were recorded during sinus rhythm and during pro...
Yamaya Y, Kubo K, Amada A, Sato K.The atrioventricular (AV) conductive functions were investigated before and after the pharmacological autonomic nervous blockade (PAB) through the electrophysiological study on six horses (AV block group) in which the dropped beats occurred more frequently (over 200 beats/24 hr) and on five horses (control group) in which the dropped beats occurred sporadically (under 200 beats/24 hr) or in which the arrhythmias were not recognized at all on the long-term electrocardiogram. As a result, AV conductivity, conduction time and refractoriness in the AV block group were lower, longer and higher, res...
Darke PG, Holmes JR.The paper describes the distribution of cardiac potentials on the body surface of four horses. Potentials were recorded at 200 to 300 equallyspaced sites synchronously with a reference lead; they were measured at 10 msec. instants of time, and were plotted on diagrams. While some evidence of multiple dipolar activity occurred during each part of the cardiac cycle, the majority of potentials arose as if from a single resultant dipole.
Strain GM, Taylor DS, Graham MC, Kamerling SG.Cortical somatosensory-evoked potentials (SEP) were recorded from thoracic and pelvic limbs in 15 horses (13 Thoroughbreds and 2 Quarter Horses). Ulnar nerve SEP were evoked by electrical stimulation of the lateral palmar branch of the ulnar nerve at the level of the metacarpophalangeal joint. Recordings were taken between electrodes at 2 cm lateral to the vertex (contralateral to the stimulated limb) and the midpoint of the interorbital line. Four peaks were found in all recordings: N1, P1, N2, and P2. Latencies to the peaks were 39.0 +/- 2.7, 45.5 +/- 5.3, 50.4 +/- 5.2, and 62.3 +/- 3.7 ms (...
Holmes JR.The paper describes the spatial vector changes during ventricular depolarisation in 190 horses using a semi-orthogonal ECG lead system. The replacement of planar vector loops by a plot of 3 parameters to depict the changing spatial vector, with a time base on the X axis, is described and illustrated. Some horses with diastolic murmurs and some with a history of respiratory problems formed 2 distinct groups. As a result of these findings a possible relationship between the vector changes and the anatomical siting of the ventricles is suggested and discussed. Attention is drawn to certain measur...
Kozelek P, Holcik J, Sedlinska M.The paper describes experiments and their results that offered an insight to relationship between RR and QT intervals in equine ECG signals recorded under various conditions. In contrast to human heart in a great number of cases the QT intervals prolonged with a heart rate acceleration. Peak-to-peak differences between maximum and minimum RR intervals during the excitation response in non-standard responses were twice as smaller as in standard responses and the lengths of QT intervals were significantly longer in the non-standard records. This fact means that the electrical processes in equine...
Miller PJ, Holmes JR.Beat-to-beat variation in the amplitude of the QRS waveform from 13 horses with second degree partial atrioventricular block was examined using an orthogonal lead (X,Y,Z) system. The peak positive deflections (XR, YR and ZR) and peak negative deflections (XQS, YS and ZQ) were regressed against PR and RR intervals. XQS was used to indicate that the peak negative deflection in X could have been a Q or S wave. XR and YR were directly related to PR (P less than 0.001) and XQS and YS were inversely related to PR (P less than 0.001). YR was also directly related to RR (P less than 0.001) but not so ...
Hudson NP, Mayhew IG, Pearson GT.Intracellular microelectrode recordings were made from smooth muscle cells in cross-sectional preparations of equine ileum, superfused in vitro. Membrane potential oscillations and spike potentials were recorded in all preparations, but recordings were made more readily from cells in the longitudinal muscle layer than from cells in the circular layer. The mean (se) resting membrane potential (RMP) of smooth muscle cells in the longitudinal muscle layer was -51.9 (1.2) mV, and the membrane potential oscillations in this layer had a mean amplitude of 4.8 (0.4) mV, a frequency of 9.0 (0.1) cycles...
von Engelhardt W, Rösel E, Rechkemmer G.Short circuit current (ISC) and transepithelial conductance (gt) across sheets of epithelia were measured in the caecum, the proximal and the distal colon of pig, sheep, pony, rat and guinea pig. The electrical parameters underline the basic segmental and species differences. The diversity of ISC demonstrates the different nature of electrogenic transport mechanisms, and data clearly show the heterogeneity with respect to transport mechanisms along the large intestine in the various species. The great differences in amiloride sensitive ISC indicate the variabilities in the electrogenic Na tran...
Geddes LA, Bourland JD, Tacker WA.The threshold energy and current required for ventricular defibrillation was determined in dogs ranging in weight from 6.4 to 38 kg and in ponies ranging in weight from 40 to 101 kg. Trapezoidal waves, 10 ms in duration, with 10%, 50%, 70%, and 90% tilt were applied to transchest electrodes. For all values of tilt, the energy and current required increased with body weight. The energy dose (joules per kilogram of body weight) was higher for the heavier animals, whereas the current dose (peak amperes per kilogram of body weight) was essentially the same for dogs and ponies. In both species and ...
Haugaard MM, Pehrson S, Carstensen H, Flethøj M, Hesselkilde EZ, Praestegaard KF, Diness JG, Grunnet M, Jespersen T, Buhl R.Only few pharmacologic compounds have been validated for treatment of atrial fibrillation (AF) in horses. Studies investigating the utility and safety of flecainide to treat AF in horses have produced conflicting results, and the antiarrhythmic mechanisms of flecainide are not fully understood. Objective: To study the potential of flecainide to terminate acutely induced AF of short duration (≥ 15 minutes), to examine flecainide-induced changes in AF duration and AF vulnerability, and to investigate the in vivo effects of flecainide on right atrial effective refractory period, AF cycle length...
Kikuchi K, Kozai K, Hojo T, Sakatani M, Okuda K, Bai H, Kawahara M, Takahashi M.We investigated the electrical impedance of the reproductive tracts (vagina and uterine endometrial tissues) and the expression of mucus-related genes to identify the stage of the estrous cycle in mares. We first examined vaginal impedance in native Hokkaido mares during their estrous cycle and found no significant differences. However, impedance levels tended to decrease towards ovulation. Furthermore, we investigated the estrous cycle by measuring the electrical impedance of the uterine endometrial tissues obtained from carcasses of mares. We found that impedance levels in the endometrial ti...
Rakestraw PC, Snyder JR, Sanders KM, Shuttleworth WC.To evaluate electrical activity of jejunal circular muscle in horses and characterize electrical responses to stimulation by intrinsic inhibitory neurons. Methods: Portions of jejunum obtained from horses euthanatized for reasons other than gastrointestinal tract disease. Methods: Isolated circular muscle preparations were perfused with oxygenated modified Krebs solution. Glass microelectrodes were used for intracellular recording of membrane potentials from single smooth muscle cells. Electrical activity and responses to electrical field stimulation (EFS) of intrinsic neurons in the presence ...
