Continuous electrocardiogram monitoring in porcine model of myocardial ischemia reperfusion

Abstract

As cardiovascular disease is the leading cause of global mortality, innovative animal models are vital to demonstrating the translational value of experimental discoveries. Investigations focused on myocardial remodeling after ischemia reperfusion (I/R) are well suited to a porcine model, but the evolution of that injury and its impact on electrical conductivity or arrhythmia threshold have been difficult to monitor continuously. Multiple electrode telemetry devices may be fitted to the animals but are costly and prone to damage. Implantable telemetry devices are likewise expensive, carry surgical risk, and are often verified only for single use. Here, we report the utilization of the commercially available Fourth Frontier X2 external telemetry device for continuous monitoring of heart rate and rhythm after myocardial I/R injury in pigs, highlighting sustained monitoring across a 7‐day study.

Wearable technology for continuous electrocardiogram monitoring can be utilized in porcine models of disease.

1. INTRODUCTION

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, accounting for 18.6 million deaths in 2019. ¹ , ² Therefore, clinically relevant animal models that possess comparable coronary anatomy and intact arrhythmogenic machinery are vital for mimicking human CVD pathology and subsequent treatment effects. ³ , ⁴ , ⁵ Small animal models of CVD, such as mouse, rat, and guinea pig, although scalable, do not have the ability to exhibit arrhythmogenesis due to physiological limitations of the heart. ³ , ⁶ , ⁷ , ⁸ , ⁹ , ¹⁰ Meanwhile, large animal models such as porcine and nonhuman primates have emerged as powerful translational models to study ischemia–reperfusion (I/R) injury pathology and to measure the effects of cardiac therapy, overcoming previous limitations in providing a physiologically similar model to that of humans. ¹¹ , ¹² , ¹³ Numerous porcine cardiac injury models have been developed, ranging from acute I/R, in which coronary artery occlusion and reperfusion are followed by same‐day treatment, to chronic heart failure models in which treatment is administered weeks after initial cardiac injury. ¹⁴ , ¹⁵ In addition, the longevity that porcine models provide to study long‐term effects of CVD treatment is significant, as long‐term safety and efficacy studies are necessary for interventions aiming to transition into a clinical setting. ¹¹ , ¹⁶ Porcine models provide a translational platform for researchers to study CVD and its treatment through physiological relevance, enabling studies to investigate the arrhythmogenic effects of treatment long term. ¹⁵

To date, numerous studies have utilized implantable loop recorders such as the Reveal LINQ cardiac monitoring system (Medtronic, USA), M01 Telemetry device (DSI, USA), or EasyTEL+ (emka Technologies, France) to monitor cardiac rate and rhythm (Table 1). ¹³ , ¹⁴ , ¹⁵ Although implantable telemetry devices provide constant, high‐quality electrocardiogram (EKG) monitoring, surgical implantation is invasive and cost prohibitive. ¹⁷ With the increased use of wearable telemetry devices over the past 10 years for recreational use and health monitoring, numerous platforms are viable candidates to provide constant EKG recordings in a research setting. Here, we propose the use of the commercially available Fourth Frontier X2 (FF2) wearable telemetry device as a cost‐effective, reusable, and minimally invasive means to monitor porcine telemetry over an experimental study of porcine I/R injury. The FF2 device, a smart heart monitor, allows for continuous monitoring of heart rate and rhythm using a single‐lead, 125‐Hz sampling rate affixed to a strap wrapped around the body. ¹⁸ Table 1 indicates that the expense of this reusable, externally applied device is a fraction of currently available implantable devices. This project aims to highlight the feasibility of the FF2 device as a viable alternative to the current standards in a 7‐day I/R porcine model. Success in this under these experimental conditions can establish FF2 as a viable option for models requiring long‐term cardiac monitoring, such as ischemic cardiomyopathy and heart failure.

TABLE 1.

Parameters for implantable cardiac monitoring devices used in porcine models.

Device	Manufacturer	EKG monitor placement	Study	Reusability	Estimated cost per device ($)
M01 Telemetry device	Data Sciences International (DSI), USA	Leads placed within the chest wall adjacent to the base and apex of the heart	Human embryonic stem cell‐derived cardiomyocytes regenerate the infarcted pig heart but induce ventricular tachyarrhythmias	None	1743
EasyTEL+	emka Technologies, France	Implanted in a subcutaneous pocket that was created in the left flank	Cellular heterogeneity of pluripotent stem cell‐derived cardiomyocyte grafts is mechanistically linked to treatable arrhythmias	None	4220
Reveal LINQ cardiac monitoring system	Medtronic, USA	Subcutaneously placed in the left paraspinal region inferior to the angle of the scapula in pigs after surgery	Pluripotent stem cell‐derived committed cardiac progenitors remuscularize damaged ischemic hearts and improve their function in pigs	None	4500
Frontier X2	Fourth Frontier, USA	Externally affixed to chest strap, which is sutured onto the pig		Yes	600

Abbreviation: EKG, electrocardiogram.

2. TECHNIQUE

All animal care and surgical procedures were approved by the Medical University of South Carolina Institutional Animal Care and Use Committee (IACUC, AR2020‐00945). Establishing this technique for noninvasive continuous EKG monitoring was part of a larger porcine investigation; therefore, the animal care expectations to achieve IACUC approval included compliance with ARRIVE (Animal Research: Reporting In Vivo Experiments) guidelines. Results of that full investigation will be reported elsewhere.

Castrated male Yorkshire cross pigs (30–40 kg, Premier BioSource, Indiana, USA) were housed under a 12‐h light–dark cycle and fed ad libitum (Purina lab‐diet 5084). The Cardiovascular Surgery Research Laboratory at the Medical University of South Carolina has experience with a porcine myocardial I/R model ¹⁹ , ²⁰ , ²¹ ; therefore, this protocol was utilized in this project aimed at establishing the efficacy and feasibility of utilizing the FF2 monitor for continuous EKG monitoring after a cardiac procedure.

After initiation of general anesthesia, the animals underwent left lateral anterior thoracotomy. The pericardium was opened longitudinally, and dissection of the epicardial fat allowed visualization of the circumflex artery. After the first obtuse marginal artery (OM1) was identified, the animal was treated with intravenous heparin (100 units/kg). Due to known irritability of the porcine heart during manipulation near the left atrium, antiarrhythmic medications, including amiodarone (250 mg) and lidocaine (70 mg), were administered, and the circumflex artery was occluded with a silk loop just proximal to OM1 (Figure 1A). A triangular wedge of cyanotic myocardium was visualized, and ST segment elevations were observed in Lead II on intraoperative EKG (Figure 1B). After 60 min of ischemia, the loop was released and reperfusion was achieved. A 5 French catheter was inserted through a 16‐gauge needle puncture site in the pulmonary artery and secured with a 5‐0 Prolene suture. This line was then tunneled to the dorsal aspect of the pig and secured within a port pocket overlying the paraspinal musculature for future access. This port position was caudal to the thoracotomy to avoid overlap with the subsequent FF2 telemetry strap placement. The thoracotomy was closed with approximation of ribs, musculature, and skin in standard fashion.

FIGURE 1.

(A) Silk tie occlusion of circumflex artery and cyanotic wedge of ischemic myocardium outlined by purple marker. (B) ECG tracing in Lead II at baseline, with occlusion, reperfusion, and recovery.

The telemetry heart rate and rhythm monitor used in this study was the FF2 device from Fourth Frontier (USA) that is commercially available. The FF2 monitor is now FDA 510k cleared for early detection of arrhythmias in humans, strengthening potential veterinary use in a porcine model. ¹⁸ To position the FF2 monitor, the point of maximal impulse (PMI) was palpated, and the strap was placed circumferentially at this level. After the monitor was snapped to the strap, the sensors were placed over the PMI (Figure 2A) and the Bluetooth function was initiated to sync with the investigator's phone and FF2 application. Initiating a “Run” activity enabled the device to begin recording the EKG activity, and this can be continued for up to 24 h. When the electrodes established adequate contact, the application screen showed a value for “heart rate,” and this was matched to the rate on the anesthesia monitor (Figure 2B). Maintaining electrode to skin contact was an initial challenge, and best practice included stitching the circumferential band into place utilizing Nylon suture (Figure 2A); the risk of dislodging the monitor from the caged animals was minimized by covering the region with an athletic tank top (Figure 2C). It is advisable to house the pigs individually. The battery life of each monitor is 48 h; therefore, the “Run” data were synced and uploaded to the online account every 24 h, and the physical monitors were exchanged on each pig every 48 h. The online platform allows retrospective review of the EKG tracing to assess arrhythmia events (Figure 3A), and this function can be of particular advantage for investigations impacting myocardial recovery and electrical activity. Additionally, the online platform shows a pie chart, highlighting high‐quality recordings alongside noisy signal (Figure 3B). To highlight FF2 efficacy in capturing quality EKG recordings, we used a 7‐day protocol after a porcine I/R injury, summarized in Table 2.

FIGURE 2.

(A) Placement of Fourth Frontier X2 device over the PMI, stabilized with strap and sutures. (B) Telemetry detection verified with the intra‐operative EKG. (C) Device protection by covering with athletic tank top.

FIGURE 3.

Fourth Frontier Dashboard demonstrating (A) multiple hemodynamic parameters, direct visualization of ECG segments, and (B) capture duration with data quality assessment.

TABLE 2.

Data quality per day for FF2 tracking of porcine EKG.

Day of study	Percentage of quality data
1	95.82
2	97.84
3	97.44
4	93.45
5	84.06
6	83.27

Abbreviations: EKG, electrocardiogram; FF2, Fourth Frontier X2.

3. CONCLUSION

With the current popularity of wearable monitoring devices and expected growth in this market, application to translational animal models of cardiac disease represents an opportunity to leverage the newest technology and optimize the relevance of research initiatives aimed to reduce cardiovascular mortality.

AUTHOR CONTRIBUTIONS

Nathaniel Hyams: Conceptualization; data curation; investigation; methodology; software; writing – original draft; writing – review and editing. Roxanne Swagel: Data curation; methodology; project administration; writing – review and editing. Sharon Thomas: Data curation; methodology; project administration; writing – review and editing. Rupak Mukherjee: Conceptualization; data curation; methodology; software; writing – review and editing. Alicia Braxton Hickman: Conceptualization; formal analysis; methodology; supervision; writing – review and editing. Daniel Eldridge: Data curation; methodology; supervision; writing – review and editing. Kristine Helke: Conceptualization; methodology; project administration; supervision; writing – review and editing. Ying Mei: Conceptualization; data curation; funding acquisition; methodology; supervision; writing – review and editing. Jean Marie Ruddy: Conceptualization; data curation; funding acquisition; methodology; project administration; software; validation; writing – original draft; writing – review and editing.

FUNDING INFORMATION

This research received funding from College of Graduate Studies, Medical University of South Carolina, Grant/Award Number: SCTR 2305; National Heart, Lung, and Blood Institute, Grant/Award Number: 1U01HL169361‐01; NIH: NCATS, Grant/Award Number: UL1TR001450.

CONFLICT OF INTEREST STATEMENT

The authors have no conflict of interest to report.

ETHICS STATEMENT

All animal care and surgical procedures were approved by the Medical University of South Carolina Institutional Animal Care and Use Committee (IACUC, AR2020‐00945).