This work was funded by the National Institutes of Health, grant numbers R01NS100954 and R01NS099188.

The authors have nothing to disclose.

Practicing and mastering the SAN dissection process is imperative since the tissue is fragile and healthy tissue is necessary for a successful recording. During the SAN dissection, correct orientation is essential to obtain the proper region of tissue. However, the original orientation of the heart can be easily lost during the dissection process, which complicates this endeavor. Therefore, to ensure the proper left-right orientation, the atria should be visually inspected. Typically, the right atrium tends to be more tr...

The heart is a complex organ governed by both cardiac-intrinsic and extrinsic influences such as those that originate in the brain. The sinoatrial node (SAN) is a defined region in the heart that houses the pacemaker cells (also referred to as sinoatrial cells, or SA cells) responsible for the initiation and perpetuation of the mammalian heartbeat1,2. The intrinsic heart rate is the rate driven by the pacemaker cells without influence by other cardiac or neuro-humoral influences, but traditional measures of heart rate in humans and live animals, such as electrocardiograms, reflect both the pacemaker and neural influences on the heart. The most notable neural influence on SA cells is from the autonomic nervous system, which constantly modulates firing patterns to meet the physiological requirements of the body3. Supporting this idea, both sympathetic and parasympathetic projections can be found near the SAN4. The intrinsic cardiac nervous system (ICNS) is another important neural influence where ganglionated plexi, specifically in the right atria, innervate and regulate the activity of the SAN5,6.
Understanding pacemaking deficits is clinically important, as dysfunction can underlie many cardiac disorders, as well as contribute to the risk of other complications. Sick sinus syndrome (SSS) is a category of diseases characterized by dysfunction of the sinoatrial node which impedes proper pacemaking7,8. SSS can present with sinus bradycardia, sinus pauses, sinus arrest, sinoatrial exit block, and alternating bradyarrythmias and tachyarrhythmias9 and can lead to complications including increased risk of embolic stroke and sudden death8,10. Those with Brugada syndrome, a cardiac disorder marked by ventricular fibrillation with an increased risk of sudden cardiac death, are at greater risk for arrhythmogenic events if they also have comorbid SAN dysfunction11,12. Sinoatrial dysfunction may also have physiological consequences beyond the heart. For example, SSS has been observed to trigger seizures in a patient due to cerebral hypoperfusion13.
To identify sinoatrial pacemaking deficits, intrinsic heart rates need to be determined by measuring the activity of the SAN without the influence of the autonomic nervous system or humoral factors. Clinically, this can be approximated by pharmacological autonomic blockade14, but this same technique can also be applied in mammalian models to study intrinsic cardiac function15,16. While this approach blocks a large portion of contributing neural influences and allows for in vivo cardiac examination, it does not completely eliminate all extrinsic influences on the heart. Another research technique used to study intrinsic cardiac function in animal models is isolated heart recordings using Langendorff-perfused hearts, which typically involve measurements using electrograms, pacing, or epicardial multielectrode arrays17,18,19,20. While this technique is more specific to cardiac function since it involves removing the heart from the body, the measurements may still be influenced by mechano-electric autoregulatory mechanisms that could influence intrinsic heart rate measurements21. The isolated heart recordings may also still be influenced by autonomic regulation through the ICNS5,6,22,23. Furthermore, maintaining a physiologically relevant temperature of the heart, which is critical for cardiac function measurements, can be difficult in isolated heart approaches20. A more direct method to study SAN function is to specifically isolate SAN tissue and measure its activity. This can be accomplished through SAN strips (isolated SAN tissue) or isolated SAN pacemaker cells24,25. Both require a high degree of technical training, as the SAN is a very small and highly defined region, and cell isolation poses an even greater challenge as dissociation can damage the overall health of the cell if not performed correctly. Furthermore, these techniques require expert electrophysiological skills in order to successfully record from the tissue or cells using individual recording microelectrodes.
In this protocol, we describe a technique to record the SAN in vitro by using a microelectrode array (MEA) to obtain intrinsic heart rate measurements. This approach has the advantage of making highly specific electrophysiological recordings accessible to researchers lacking intensive electrophysiological skillsets. MEAs have previously been used to study cardiomyocyte function in primary cardiomyocyte cultures26,27,28,29,30,31,32, cardiac sheets33,34,35,36,37,38,39, and tissue whole mounts40,41,42,43,44,45,46,47. Previous work has also been done to examine field potentials in SAN tissue41,42. Here, we provide a methodology to use the MEA to record and analyze murine intrinsic SAN firing rates. We also describe how this technique can be used to test pharmacological effects of drugs on SAN intrinsic firing rates by providing a sample experiment showing the effects of 4-aminopyridine (4-AP), a voltage-gated K+ channel blocker. Using defined anatomical landmarks, we can accurately record the SAN without having to perform the extensive tissue dissections or cell isolations required in other methods. While the MEA can be cost-prohibitive, the recordings provide highly specific and reliable measures of pacemaking that can be used in a vast array of clinical and physiological research applications.

<table><tbody><tr><td>4-Aminopyridine</td><td>Sigma</td><td>A78403-25G</td><td></td></tr><tr><td>22 gauge syringe needle</td><td>Fisher Scientific</td><td>14-826-5A</td><td>Used for dissection</td></tr><tr><td>23 gauge syringe needle</td><td>Fisher Scientific</td><td>14-826-6C</td><td>Used for dissection</td></tr><tr><td>60mm Petri Dishes</td><td>Genesee Scientific</td><td>32-105G</td><td></td></tr><tr><td>500mL Pyrex Bottle</td><td>Fisher Scientific</td><td>06-414-1C</td><td>Used to store solutions</td></tr><tr><td>1000 mL Pyrex Bottle</td><td>Fisher Scientific</td><td>06-414-1D</td><td>Used to store solutions</td></tr><tr><td>Bone Forceps</td><td>Fine Science Tools</td><td>16060-11</td><td></td></tr><tr><td>Calcium chloride dihydrate (CaCl&lt;sub&gt;2&lt;/sub&gt;&amp;middot;2H&lt;sub&gt;2&lt;/sub&gt;O)</td><td>Sigma-Aldrich</td><td>C5080-500G</td><td></td></tr><tr><td>Carbogen (95% O&lt;sub&gt;2&lt;/sub&gt;, 5% CO&lt;sub&gt;2&lt;/sub&gt;)</td><td></td><td></td><td></td></tr><tr><td>Castroviejo Scissors, 4&quot;</td><td>Fine Science Tools</td><td>15024-10</td><td></td></tr><tr><td>D-(+)-Glucose</td><td>Sigma-Aldrich</td><td>G7021-1KG</td><td></td></tr><tr><td>Data Acquisition PC</td><td></td><td></td><td>CPU: Intel Xeon or Intel Core i7, Memory: 8GB, HDD: 1TB, Graphic Card: NVIDIA or On-board, Screen: 1920x1080</td></tr><tr><td>Dissection Microscope</td><td>Jenco</td><td></td><td></td></tr><tr><td>Dissecting Pins</td><td>Fine Science Tools</td><td>26002-20</td><td></td></tr><tr><td>Dumont #2 Laminectomy Forceps</td><td>Fine Science Tools</td><td>11223-20</td><td></td></tr><tr><td>Dumont #55 Forceps</td><td>Fine Science Tools</td><td>11295-51</td><td></td></tr><tr><td>&amp;nbsp;Extra Fine Graefe Forceps</td><td>Fine Science Tools</td><td>11152-10</td><td></td></tr><tr><td>Glass Chamber</td><td>Grainger</td><td>49WF30</td><td>Used for mouse euthanization</td></tr><tr><td>Harp Anchor Kit</td><td>Warner Instruments</td><td>&amp;nbsp;SHD-22CL/15 WI 64-0247</td><td></td></tr><tr><td>HCl</td><td>Fisher Chemicals</td><td>SA48-4</td><td>Used for pH balancing</td></tr><tr><td>Hemostat</td><td>Fine Science Tools</td><td>13013-14</td><td></td></tr><tr><td>Heparin</td><td>Aurobindo Pharma Limited IDA, Pashamylaram</td><td>NDC 63739-953-25</td><td></td></tr><tr><td>HEPES</td><td>Sigma-Aldrich</td><td>H3375-250G</td><td></td></tr><tr><td>Inverted Microscope</td><td>Motic</td><td>AE2000</td><td></td></tr><tr><td>Isoflurane</td><td>Patterson Veterinary</td><td>07-893-1389</td><td></td></tr><tr><td>Lab Tape</td><td>Fisher Scientific</td><td>15-950</td><td></td></tr><tr><td>Light for Dissection Microscope</td><td>Dolan-Jenner</td><td>MI150DG 660000391014</td><td></td></tr><tr><td>Magesium chloride (MgCl&lt;sub&gt;2&lt;/sub&gt;)</td><td>Sigma-Aldrich</td><td>208337-100G</td><td></td></tr><tr><td>MED64 Head Amplifier</td><td>MED64</td><td>MED-A64HE1S</td><td></td></tr><tr><td>MED64 Main Amplifier</td><td>MED64</td><td>MED-A64MD1A</td><td></td></tr><tr><td>MED64 Perfusion Cap</td><td>MED64</td><td>MED-KCAP01</td><td></td></tr><tr><td>MED64 Perfusion Pipe Holder Kit</td><td>MED64</td><td>MED-KPK02</td><td></td></tr><tr><td>MED64 ThermoConnector</td><td>MED64</td><td>MED-CP04</td><td></td></tr><tr><td>Mesh</td><td>&amp;nbsp;Warner Instruments</td><td>640246</td><td></td></tr><tr><td>Microelectrode array (MEA)</td><td>Alpha Med Scientific</td><td>MED-R515A</td><td></td></tr><tr><td>Mobius Software</td><td>WitWerx Inc.</td><td></td><td>Specific software for the MED64</td></tr><tr><td>NaOH</td><td>Fisher Chemicals</td><td>S320-500</td><td>Used for pH balancing</td></tr><tr><td>Normal Saline</td><td>Ultigiene</td><td>NDC 50989-885-17</td><td></td></tr><tr><td>Paint Brush</td><td>Fisher Scientific</td><td>NC1751733</td><td></td></tr><tr><td>Parafilm</td><td>Genesee Scientific</td><td>PM-996</td><td></td></tr><tr><td>Peristaltic Pump</td><td>Gilson</td><td>F155009</td><td></td></tr><tr><td>Peristaltic Pump Tubing</td><td>Fisher Scientific</td><td>14-171-298</td><td>1/8&#039;&#039; Interior Diameter</td></tr><tr><td>Polyethyleneimine</td><td>Sigma</td><td>P3143</td><td></td></tr><tr><td>Potassium chloride (KCl)</td><td>Sigma-Aldrich</td><td>P9333-500G</td><td></td></tr><tr><td>Potassium phosphate monobasic (KH&lt;sub&gt;2&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt;)</td><td>Sigma-Aldrich</td><td>P5655-500G</td><td></td></tr><tr><td>Sodium Bicarbonate</td><td>Sigma</td><td>S6297</td><td></td></tr><tr><td>Sodium chloride (NaCl)</td><td>Fisher Scientific</td><td>S671-3</td><td></td></tr><tr><td>Sylgruard Elastomer Kit</td><td>Dow Corning</td><td>184 SIL ELAST KIT 0.5KG</td><td></td></tr><tr><td>Sodium Phosphate Monobasic</td><td>Sigma</td><td>S6566</td><td></td></tr><tr><td>Sodium tetraborate</td><td>Sigma</td><td>S9640</td><td></td></tr><tr><td>Surgical Scissors</td><td>Fine Science Tools</td><td>14074-09</td><td></td></tr><tr><td>Transfer Pipets (3mL graduated)</td><td>Samco Scientific</td><td>225</td><td></td></tr></tbody></table>

microelectrode array recording of sinoatrial node firing rate to identify intrinsic cardiac pacemaking defects in mice

The sinoatrial node (SAN), located in the right atrium, contains the pacemaker cells of the heart, and dysfunction of this region can cause tachycardia or bradycardia. Reliable identification of cardiac pacemaking defects requires the measurement of intrinsic heart rates by largely preventing the influence of the autonomic nervous system, which can mask rate deficits. Traditional methods to analyze intrinsic cardiac pacemaker function include drug-induced autonomic blockade to measure in vivo heart rates, isolated heart recordings to measure intrinsic heart rates, and sinoatrial strip or single-cell patch-clamp recordings of sinoatrial pacemaker cells to measure spontaneous action potential firing rates. However, these more traditional techniques can be technically challenging and difficult to perform. Here, we present a new methodology to measure intrinsic cardiac firing rate by performing microelectrode array (MEA) recordings of whole-mount sinoatrial node preparations from mice. MEAs are composed of multiple microelectrodes arranged in a grid-like pattern for recording in vitro extracellular field potentials. The method described herein has the combined advantage of being relatively faster, simpler, and more precise than previous approaches for recording intrinsic heart rates, while also allowing easy pharmacological interrogation.

After allowing the tissue to acclimate in the dish for 15 min, 10 one-min traces are recorded. Our current protocol records activity for over an hour, but we have recorded stable firing patterns for &#8805;4 h in unpublished data not shown here. If an experimental preparation is good for data collection, each recording channel should exhibit consistent and evenly spaced recurring waveforms (i.e., spikes) of uniform shape for a given channel (Figure 11D). These waveforms correspond to individ...

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Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice

This protocol aims to describe a new methodology to measure intrinsic cardiac firing rate using microelectrode array recording of the whole sinoatrial node tissue to identify pacemaking defects in mice. Pharmacological agents can also be introduced in this method to study their effects on intrinsic pacemaking.

The sinoatrial node (SAN), located in the right atrium, contains the pacemaker cells of the heart, and dysfunction of this region can cause tachycardia or ...

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Research

JoVE Journal

Medicine

3.0K Views.  Southern Methodist University. Het meten van de intrinsieke hartslag is een belangrijke indicator voor de gezondheid van het hart. Deze techniek meet deze snelheid nauwkeurig, terwijl de meeste verstorende invloeden op de sinoatriale knoop worden uitgesloten. MEA-registratie van de intrinsieke hartslag legt nauwkeurige vuursnelheidsgegevens vast die vergelijkbaar zijn met eencellige opnames zonder uitgebreide elektrofysiologische training.Personen die deze techniek gebruiken, kunnen moeite hebben om gezonde weefselp...

Video: Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice

Programmed Electrical Stimulation in Mice

Genetically-modified mice have emerged as a preferable animal model to study the molecular mechanisms underlying conduction abnormalities, atrial and ventricular arrhythmias, and sudden cardiac death.1 Intracardiac pacing studies can be performed in mice using a 1.1F octapolar catheter inserted into the jugular vein, and advanced into the right atrium and ventricle. Here, we illustrate the steps involved in performing programmed electrical stimulation in mice. Surface ECG and intracardiac electrograms are recorded simultaneously in the atria, atrioventricular junction, and ventricular myocardium, whereas intracardiac pacing of the atrium is performed using an external stimulator. Thus, programmed electrical stimulation in mice provides unique opportunities to explore molecular mechanisms underlying conduction defects and cardiac arrhythmias.

Programmed electrical stimulation provides the ability to determine conduction properties of the heart, and the possibility to induce and terminate cardiac arrhythmias using various pacing protocols. Using a transvenous catheter, intracardiac electrogram recordings can be obtained in mice following programmed electrical stimulation protocols to identify arrhythmogenic substrates.

Genetically-modified mice have emerged as a preferable animal model to study the molecular mechanisms underlying conduction abnormalities, atrial and ...

Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection

Treatment of the &#8220;sick sinus syndrome&#8221; is based on artificial pacemakers. These bear hazards such as battery failure and infections. Moreover, they lack hormone responsiveness and the overall procedure is cost-intensive. &#8220;Biological pacemakers&#8221; generated from PSCs may become an alternative, yet the typical content of pacemaker cells in Embryoid Bodies (EBs) is extremely low. The described protocol combines &#8220;forward programming&#8221; of murine PSCs via the sinus node inducer TBX3 with Myh6-promoter based antibiotic selection. This yields cardiomyocyte aggregates consistent of &#62;80% physiologically functional pacemaker cells. These &#8220;induced-sinoatrial-bodies&#8221; (&#8220;iSABs&#8221;) are spontaneously contracting at yet unreached frequencies (400-500 bpm) corresponding to nodal cells isolated from mouse hearts and are able to pace murine myocardium ex vivo. Using the described protocol highly pure sinus nodal single cells can be generated which e.g. can be used for in vitro drug testing. Furthermore, the iSABs generated according to this protocol may become a crucial step towards heart tissue engineering.

This protocol describes how to produce functional sinus nodal tissue from murine pluripotent stem cells (PSC). T-Box3 (TBX3) overexpression plus cardiac Myosin-heavy-chain (Myh6) promoter antibiotic selection leads to highly pure pacemaker cell aggregates. These &#8220;Induced-sinoatrial-bodies&#8221; (&#8220;iSABs&#8221;) contain over 80% pacemaker cells, show highly increased beating rates and are able to pace myocardium ex vivo.

Treatment of the &#8220;sick sinus syndrome&#8221; is based on artificial pacemakers. These bear hazards such as battery failure and infections. Moreover, ...

Developmental Biology

Ambulatory ECG Recording in Mice

Telemetric ECG recording in mice is essential to understanding the mechanisms behind arrhythmias, conduction disorders, and sudden cardiac death. Although the surface ECG is utilized for short-term measurements of waveform intervals, it is not practical for long-term studies of heart rate variability or the capture of rare episodes of arrhythmias. Implantable ECG telemeters offer the advantages of simple surgical implantation, long-term recording of electrograms in ambulatory mice, and scalability with simultaneous recordings of multiple animals. Here, we present a step-by-step guide to the implantation of telemeters for ambulatory ECG recording in mice. Careful adherence to aseptic technique is required for favorable survival results with the possibility of implantation and recording from weeks to months. Thus, implantable ECG telemetry is a valuable tool for detection of critical information on cardiac electrophysiology in ambulatory animal models such as the mouse. 

Telemetric ECG has emerged as an essential tool in evaluating animal models for cardiac arrhythmias and sudden cardiac death. Here, we present a stepwise guide to telemetric ECG recordings for application in long-term ambulatory ECG monitoring in mice.

Telemetric ECG recording in mice is essential to understanding the mechanisms behind arrhythmias, conduction disorders, and sudden cardiac death. Although ...

Biology

Electrophysiological Assessment of Murine Atria with High-Resolution Optical Mapping

Recent genome-wide association studies targeting atrial fibrillation (AF) have indicated a strong association between the genotype and electrophysiological phenotype in the atria. That encourages us to utilize a genetically-engineered mouse model to elucidate the mechanism of AF. However, it is difficult to evaluate the electrophysiological properties in murine atria due to their small size. This protocol describes the electrophysiological evaluation of atria using an optical mapping system with a high temporal and spatial resolution in Langendorff perfused murine hearts. The optical mapping system is assembled with dual high-speed complementary metal oxide semiconductor cameras and high magnification objective lenses, to detect the fluorescence of a voltage-sensitive dye and Ca2+ indicator. To focus on the assessment of murine atria, optical mapping is performed with an area of 2 mm &#215; 2 mm or 10 mm x 10 mm, with a 100 &#215; 100 resolution (20 &#181;m/pixel or 100 &#181;m/pixel) and sampling rate of up to 10 kHz (0.1 ms) at maximum. A 1-French size quadripolar electrode pacing catheter is placed into the right atrium through the superior vena cava avoiding any mechanical damage to the atrium, and pacing stimulation is delivered through the catheter. An electrophysiological study is performed with programmed stimulation including constant pacing, burst pacing, and up to triple extrastimuli pacing. Under a spontaneous or pacing rhythm, the optical mapping recorded the action potential duration, activation map, conduction velocity, and Ca2+ transient individually in the right and left atria. In addition, the programmed stimulation also determines the inducibility of atrial tachyarrhythmias. Precise activation mapping is performed to identify the propagation of the excitation in the atrium during an induced atrial tachyarrhythmia. Optical mapping with a specialized setting enables a thorough electrophysiological evaluation of the atrium in murine pathological models.

This protocol describes the electrophysiological evaluation of murine atria utilizing an optical mapping system with a high temporal and spatial resolution, including dual recordings of the membrane voltage and Ca2+ transient under programmed stimulation through a specialized electrode catheter.

Recent genome-wide association studies targeting atrial fibrillation (AF) have indicated a strong association between the genotype and ...

Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System

Since its invention in the late 19th century, the Langendorff ex vivo heart perfusion system continues to be a relevant tool for studying a broad spectrum of physiological, biochemical, morphological, and pharmacological parameters in centrally denervated hearts. Here, we describe a setup for the modulation of the intracardiac autonomic nervous system and the assessment of its influence on basic electrophysiology, arrhythmogenesis, and cyclic adenosine monophosphate (cAMP) dynamics. The intracardiac autonomic nervous system is modulated by the mechanical dissection of atrial fat pads-in which murine ganglia are located mainly&#8212;or by the usage of global as well as targeted pharmacological interventions. An octapolar electrophysiological catheter is introduced into the right atrium and the right ventricle, and epicardial-placed multi-electrode arrays (MEA) for high-resolution mapping are used to determine cardiac electrophysiology and arrhythmogenesis. F&#246;rster resonance energy transfer (FRET) imaging is performed for the real-time monitoring of cAMP levels in different cardiac regions. Neuromorphology is studied by means of antibody-based staining of whole hearts using neuronal markers to guide the identification and modulation of specific targets of the intracardiac autonomic nervous system in the performed studies. The ex vivo Langendorff setup allows for a high number of reproducible experiments in a short time. Nevertheless, the partly open nature of the setup (e.g., during MEA measurements) makes constant temperature control difficult and should be kept to a minimum. This described method makes it possible to analyze and modulate the intracardiac autonomic nervous system in decentralized hearts.

Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System

Here, we present a protocol for the modulation of the intracardiac autonomic nervous system and the assessment of its influence on basic electrophysiology, arrhythmogenesis, and cAMP dynamics using an ex vivo Langendorff setup.

Since its invention in the late 19th century, the Langendorff ex vivo heart perfusion system continues to be a relevant tool for studying a broad spectrum ...

Electrocardiogram Recordings in Anesthetized Mice using Lead II

The electrocardiogram is a valuable tool for evaluating the cardiac conduction system. Animal research has helped generate novel genetic and pharmacological information regarding the electrocardiogram. However, making electrocardiogram measurements in small animals in vivo, such as mice, has been challenging. To this end, we used an electrocardiogram recording method in anesthetized mice with many advantages: it is a technically simple procedure, is inexpensive, has short measuring time, and is affordable, even in young mice. Despite the limitations with using anesthesia, comparisons between control and experimental groups can be performed with enhanced sensitivity. We treated mice with agonists and antagonists of the autonomic nervous system to determine the validity of this protocol and compared our results with previous reports. Our ECG protocol detected increased heart rates and QTc intervals on treatment with atropine, decreased heart rates and QTc intervals after carbachol treatment, and higher heart rates and QTc intervals with isoprenaline but did not note any change in ECG parameters on administration of propranolol. These results are supported by previous reports, confirming the reliability of this ECG protocol. Thus, this method can be used as a screening approach to making ECG measurements that otherwise would not be attempted due to high cost and technical difficulties.

We present an ECG protocol that is technically easy, inexpensive, fast, and affordable in small mice, and can be performed with enhanced sensitivity. We suggest this method as a screening approach for studying pharmacological agents, genetic modifications, and disease models in mice.

The electrocardiogram is a valuable tool for evaluating the cardiac conduction system. Animal research has helped generate novel genetic and ...

Analyzing Long-Term Electrocardiography Recordings to Detect Arrhythmias in Mice

Arrhythmias are common, affecting millions of patients worldwide. Current treatment strategies are associated with significant side effects and remain ineffective in many patients. To improve patient care, novel and innovative therapeutic concepts causally targeting arrhythmia mechanisms are needed. To study the complex pathophysiology of arrhythmias, suitable animal models are necessary, and mice have been proven to be ideal model species to evaluate the genetic impact on arrhythmias, to investigate fundamental molecular and cellular mechanisms, and to identify potential therapeutic targets.
Implantable telemetry devices are among the most powerful tools available to study electrophysiology in mice, allowing continuous ECG recording over a period of several months in freely moving, awake mice. However, due to the huge number of data points (&gt;1 million QRS complexes per day), analysis of telemetry data remains challenging. This article describes a step-by-step approach to analyze ECGs and to detect arrhythmias in long-term telemetry recordings using the software, Ponemah, with its analysis modules, ECG Pro and Data Insights, developed by Data Sciences International (DSI). To analyze basic ECG parameters, such as heart rate, P wave duration, PR interval, QRS interval, or QT duration, an automated attribute analysis was performed using Ponemah to identify P, Q, and T waves within individually adjusted windows around detected R waves. 
Results were then manually reviewed, allowing adjustment of individual annotations. The output from the attribute-based analysis and the pattern recognition analysis was then used by the Data Insights module to detect arrhythmias. This module allows an automatic screening for individually defined arrhythmias within the recording, followed by a manual review of suspected arrhythmia episodes. The article briefly discusses challenges in recording and detecting ECG signals, suggests strategies to improve data quality, and provides representative recordings of arrhythmias detected in mice using the approach described above.

Here we present a step-by-step protocol for a semiautomated approach to analyze murine long-term electrocardiography (ECG) data for basic ECG parameters and common arrhythmias. Data are obtained by implantable telemetry transmitters in living and awake mice and analyzed using Ponemah and its analysis modules.

Arrhythmias are common, affecting millions of patients worldwide. Current treatment strategies are associated with significant side effects and remain ...

Methods for the Isolation, Culture, and Functional Characterization of Sinoatrial Node Myocytes from Adult Mice

Sinoatrial node myocytes (SAMs) act as the natural pacemakers of the heart, initiating each heart beat by generating spontaneous action potentials (APs). These pacemaker APs reflect the coordinated activity of numerous membrane currents and intracellular calcium cycling. However the precise mechanisms that drive spontaneous pacemaker activity in SAMs remain elusive. Acutely isolated SAMs are an essential preparation for experiments to dissect the molecular basis of cardiac pacemaking. However, the indistinct anatomy, complex microdissection, and finicky enzymatic digestion conditions have prevented widespread use of acutely isolated SAMs. In addition, methods were not available until recently to permit longer-term culture of SAMs for protein expression studies. Here we provide a step-by-step protocol and video demonstration for the isolation of SAMs from adult mice. A method is also demonstrated for maintaining adult mouse SAMs in vitro and for expression of exogenous proteins via adenoviral infection. Acutely isolated and cultured SAMs prepared via these methods are suitable for a variety of electrophysiological and imaging studies.

Methods are demonstrated for the isolation of sinoatrial node myocytes (SAMs) from adult mice for patch clamp electrophysiology or imaging studies. Isolated cells can be used directly or can be maintained in culture to permit expression of proteins of interest, such as genetically encoded reporters.

Sinoatrial node myocytes (SAMs) act as the natural pacemakers of the heart, initiating each heart beat by generating spontaneous action potentials (APs). ...

High-resolution Optical Mapping of the Mouse Sino-atrial Node

Sino-atrial node (SAN) dysfunctions and associated complications constitute important causes of morbidity in patients with cardiac diseases. The development of novel pharmacological therapies to cure these patients relies on the thorough understanding of both normal physiology and pathophysiology of the SAN. Among the studies of cardiac pacemaking, the mouse SAN is widely used due to its feasibility for modifications in the expression of different genes that encode SAN ion channels or calcium handling proteins. Emerging evidence from electrophysiological and histological studies has also proved the representativeness and similarity of the mouse SAN structure and functions to larger mammals, including the presence of specialized conduction pathways from the SAN to the atrium and a complex pacemakers' hierarchy within the SAN. Recently, the technique of optical mapping has greatly facilitated the exploration and investigation of the origin of excitation and conduction within and from the mouse SAN, which in turn has extended the understanding of the SAN and benefited clinical treatments of SAN dysfunction associated diseases. In this manuscript, we have described in detail how to perform the optical mapping of the mouse SAN from the intact, Langendorff-perfused heart and from the isolated atrial preparation. This protocol is a useful tool to enhance the understanding of mouse SAN physiology and pathophysiology.

Here, we present a protocol for optical mapping of electrical activity from the mouse right atrium and especially the sino-atrial node, at a high spatial and temporal resolution.

Sino-atrial node (SAN) dysfunctions and associated complications constitute important causes of morbidity in patients with cardiac diseases. The ...

Optimization of Transesophageal Atrial Pacing to Assess Atrial Fibrillation Susceptibility in Mice

Mouse models of genetic and acquired risk factors for atrial fibrillation (AF) have proven valuable in investigating the molecular determinants of AF. Programmed electrical stimulation can be performed using transesophageal atrial pacing as a survival procedure, thus enabling serial testing in the same animal. However, numerous pacing protocols exist, which complicates the reproducibility. The present protocol aims to provide a standardized strategy to develop model-specific experimental parameters to improve reproducibility between studies. Preliminary studies are performed to optimize the experimental methods for the specific model under investigation, including age at the time of the study, sex, and parameters of the pacing protocol (e.g., mode of pacing and definition of AF susceptibility). Importantly, care is taken to avoid high stimulus energies, as this can cause stimulation of the ganglionic plexi with inadvertent parasympathetic activation, manifested by exaggerated atrioventricular (AV) block during pacing and often associated with artifactual AF induction. Animals demonstrating this complication must be excluded from the analysis.

The present protocol describes the optimization of experimental parameters when using transesophageal atrial pacing to assess atrial fibrillation susceptibility in mice.

Mouse models of genetic and acquired risk factors for atrial fibrillation (AF) have proven valuable in investigating the molecular determinants of AF. ...

Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice

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