Transcoronary Pacing in a Porcine Model — Impact of Guidewire Insulation

ABSTRACT: Background. Bradycardia complicating percutaneous coronary intervention (PCI) can require temporary pacing. A transcoronary approach using the guidewire in the coronary artery may be a useful alternative to transvenous pacing. The purpose of the present study was to compare the efficacy of two different coronary guidewires in transcoronary pacing: a novel guidewire (VisionWire^®, Biotronik, Germany) which has a coating to electrically insulate the shaft, thereby maximizing current delivery through the intracoronary section compared to a standard guidewire (without insulation) and a standard guidewire/balloon combination. Methods and Results. Unipolar transcoronary pacing was performed in 15 pigs under general anesthesia. In each animal, the new VisionWire was compared to a standard floppy guidewire and to a standard floppy guidewire loaded with a standard angioplasty balloon (which provides additional shaft insulation). The coronary guidewire was the cathode and a skin patch electrode (on the anterior or posterior chest wall) was the anode. We examined the effect of different electrode combinations on transcoronary pacing as assessed by threshold and impedance data and the magnitude of the epicardial electrocardiogram. Transcoronary pacing with the bare standard guidewire was effective in 77% of cases using an anterior skin patch electrode and in 87% with a posterior patch at pacing thresholds of 6.7 ± 2.9 V and 4.1 ± 3.0 V, respectively. Loading the same guidewire with an angioplasty balloon increased the pacing efficacy to 100% with significantly lower pacing thresholds of 2.4 ± 1.6 V with an anterior patch and 1.6 ± 1.3 V with a posterior patch (p Conclusions. Transcoronary pacing in the animal model is an effective technique. The VisionWire, (even without the additional insulation of a balloon in place) performed better than a standard guidewire (with or without balloon use), and enabled 100% pacing efficacy at acceptable thresholds. Thus, transcoronary pacing, particularly with specific coronary guidewires may be a useful alternative to transvenous pacing during PCI, particularly in the emergency situation when unexpected bradycardias arise during transradial angioplasty when no central venous access is immediately available for transvenous pacing. J INVASIVE CARDIOL 2011;23:108–114 ———————————————————— Neither the published literature nor recent guidelines give specific recommendations for the treatment of bradycardia complicating percutaneous coronary intervention (PCI).^1,2 The paucity of guidance on this issue may be due to the relatively low incidence of significant bradycardia during PCI, reported to occur in 1–2% of standard coronary interventions.^3,4 However, the incidence of bradycardia requiring pacing during PCI may be set to rise in an aging population, many of whom are not fit for surgical revascularization, and often present with severe coronary disease requiring complex percutaneous revascularization strategies (such as rotational atherectomy), which are known to require temporary pacing in up to half of patients.^5,6 Despite the potential for PCI to cause an increase in the incidence of profound bradycardia, the risk of bradycardia in any individual case nevertheless remains difficult to predict.⁷ The combination of unpredictability and the fact that profound bradycardia/asystole requires pacing with immediate effect are a cause for concern during PCI, hence the need to develop strategies for rapidly available pacing in any PCI context. Depending on the urgency of the situation and whether the bradycardia was predicted, the current options for emergency pacing during PCI center on percutaneous pacing or transvenous right ventricular (RV) pacing (usually via the femoral vein). Percutaneous pacing is both uncomfortable for the awake or even semiconscious patient and often unreliable (particularly in obese patients).⁸ Transvenous RV pacing is a common technique for emergency pacing during PCI. However, prophylactic insertion of a femoral vein access temporary pacing wire increases procedural time, costs and risks. These risks include cardiac perforation with tamponade,⁹ ventricular arrhythmias,^3,10–12 deep vein thrombosis with subsequent pulmonary embolism and vascular complications.¹³ Such complications are reported to occur in up to 20% of cases.¹⁴ Emergency insertion of a temporary wire in sudden unpredicted bradycardia or asystole is challenging to the interventional cardiologist and can be detrimental to the patient if not immediately successful. Given the increasing use of the radial artery as access for PCI, the emergency insertion of a transvenous pacing wire is even more challenging because there is no suitable vein near the radial artery and often an unsterile body region (usually the groin) must be prepared and draped before temporary wire insertion can begin. With this background, unipolar transcoronary pacing (using the guidewire already in the coronary artery undergoing PCI) and an adhesive skin patch electrode is an attractive solution to some of these problems. First described by Meier et al,¹⁵ this technique has been shown to be reliable in several human and animal studies.^4,16,17 Our group studied transcoronary pacing in 70 patients undergoing PCI and demonstrated that although there was an 85% pacing efficacy with the technique, the effective pacing thresholds using a bare guidewire and a skin patch electrode in the groin were higher than compared to the transvenous approach.⁷ To further investigate the practical aspects of transcoronary pacing, we developed an animal model with which we demonstrated that optimizing the skin patch position (on the posterior chest wall) and using a standard monorail angioplasty balloon (which provides further insulation of the guidewire) resulted in pacing thresholds comparative to those obtained by standard transvenous pacing in the RV apex.¹⁸ The purpose of the present study was to examine a novel guidewire with a special coating for electrical insulation — the VisionWire^® (Biotronik, Berlin, Germany) — in transcoronary pacing in comparison to a bare standard guidewire and a standard guidewire additionally insulated by a monorail balloon. Since the VisionWire is, at present, only certified for temporary pacing in the coronary veins,¹⁹ this study could only be done in an animal model.

Methods

Transcoronary guidewire pacing was evaluated in 15 adult pigs in an animal catheterization laboratory as described previously.¹⁸ The study was conducted according to the regulations of the local animal-based research authorities. General anesthesia was induced and maintained with isoflurane, nitrous oxide and ketamine (adapted to body weight) in all animals. Mechanical ventilation was instituted while the animal was placed in the supine position on the table of a monoplane catheterization laboratory. A 6 French (Fr) sheath was placed in the carotid artery for coronary access and transcoronary pacing and another 6 Fr sheath was inserted into the internal jugular vein for transvenous pacing. Sufficient anticoagulation to avoid thrombus formation during coronary angiography and pacing was established by unfractionated heparin at 70 units per kilo body weight at the beginning of the procedure. Coronary angiography was performed with iopamidol 370 (Solutrast, Fa. Altana, Konstanz, Germany) at body temperature. Angiography of both coronary arteries was done using standard 6 Fr Judkins guiding catheters (Cordis Corp., Miami Lakes, Florida) for visualization of the coronary anatomy and exclusion of coronary artery disease. Pacing technique. Transcoronary guidewire pacing was performed in a unipolar setting against indifferent skin patch electrodes. The coronary guidewire served as the cathode in all cases.20 To achieve this, the tip of the coronary guidewire was advanced into a distal branch of the target coronary artery, either of the main vessel itself, or into a small side branch (Figure 1). Each coronary artery was used for transcoronary pacing while wired by each of the three guidewire/balloon combinations in turn. The three coronary wire groups were: the new VisionWire^® guidewire alone (Biotronik, Berlin, Germany), a standard floppy-guidewire (Galeo floppy^®, Biotronik) alone, and finally, a standard floppy guidewire (Galeo floppy) loaded with a standard monorail coronary angioplasty balloon and the balloon tip just reaching the beginning of the radiopaque end of the guidewire (Figure 1, inset). The uncoated stiff end of the study guidewire was connected by a sterile alligator clamp to the cathode of an external pulse generator (model 3105, Guidant Corp., St. Paul, Minnesota) with a maximum output of 10 V at a maximum pulse width of 2.5 ms. Two self-adhesive skin patch electrodes with a surface area of about 100 cm² served as indifferent electrodes and were connected to the anode of the pulse generator. These skin patch electrodes were placed on the anterior and posterior chest wall of the animal as described previously.¹⁸ Finally, a transvenous electrode was placed via the jugular vein sheath into the apex of the right ventricle. To allow a comparison of the transcoronary pacing with transvenous pacing, the latter was performed in a bipolar setup equally as far as in a unipolar setup against the skin patch electrodes. Pacing protocol. According to our pacing protocol, the guidewire was advanced through the guiding catheter into the first target vessel. The back of the guidewire (outside the animal) was connected to the cathode of the external pacemaker by a sterile alligator clamp. The anodal electrode of the pacemaker was connected consecutively with the skin patches on the anterior and posterior chest wall. Before transcoronary pacing was initiated, the magnitude of the epicardial electrocardiogram (ECG) — the R-wave — was measured. Transcoronary pacing was then started at a rate of 10–20 beats per minute faster than the intrinsic heart rate (usually about 80–100/min) at the maximum device output of 10 V with 2.5 ms impulse duration. Output voltage was sequentially reduced until the pacing threshold was reached. Pacing was continued above the pacing threshold for several seconds to measure the pacing impedance. If no effective pacing was achieved in a specific vessel after repositioning the guidewire three times, the pacing threshold was set to 10 V. These transcoronary pacing procedures were performed against both anodal skin patch electrodes positions (anterior and posterior) and repeated with the guidewire positioned in all three coronary arteries consecutively. Following completion of the transcoronary pacing protocol, the guidewire was removed and inspected for adherence of thrombotic material. All measurements were repeated with the second guidewire. Finally a small monorail angioplasty balloon was advanced over the standard floppy wire until the beginning of the radiopaque end of the guidewire and a third complete data set was acquired. Animal characteristics. Coronary pacing was applied in 15 adult pigs (body weight 26.4 ± 1.1 kg; length 120 ± 2 cm). All animals were kept under identical conditions for 1 month before the beginning of the study. Statistical analysis. All descriptive analyses describe mean and standard deviations of the data. Spearman coefficients with p-values were calculated to describe linear association between the measurement of pacing thresholds, impedances and R-waves. A mixed model to describe repeated measurements was fitted with fixed effects. Measurements were repeated at two anodal electrodes and three guidewire setups in each pig. A common correlation among the observations from a single pig was assumed corresponding to the compound symmetry structure. To describe the influence of fixed effects and their interactions, an ANOVA F-type statistic was used. All the reported p-values are two-sided and have not been adjusted for multiple testing, p-values Results Coronary artery disease or coronary abnormalities were excluded in all 15 animals. The guidewire was successfully advanced into all three coronary arteries without complications, so that we could obtain a full data set according to our pacing protocol in all 15 pigs. Transcoronary pacing. Transcoronary guidewire pacing with the bare floppy guidewire against the anterior skin patch electrode was effective in 13/15 animals in the right coronary artery (RCA) (86%) and 11/15 animals in both the right circumflex artery (RCX) and in the left anterior descending artery (LAD) (74%). Using the posterior skin patch electrode, transcoronary pacing was successful in 14/15 animals in the RCA (93%), 12/15 animals in the RCX (80%) and 13/15 animals in the LAD (87%). Thus, the pacing efficacy with the bare floppy guidewire was 77% with the anterior skin patch and 87% with the posterior skin patch electrode. Guidewire pacing with the VisionWire and with the balloon-isolated floppy-guidewire was effective in 100% against both indifferent skin patch electrodes in all vessels attempted. Pacing thresholds. Threshold data for the VisionWire, the bare floppy guidewire and the balloon-insulated floppy guidewire are shown in Table 1. Using the anterior skin patch electrode, the VisionWire yielded a mean pacing threshold at 1.6 ± 0.7 V, significantly lower than the threshold obtained with the bare floppy guidewire at 6.7 ± 2.9 V. Insulation of the floppy guidewire by the angioplasty balloon decreased the pacing threshold to 2.4 ± 1.6 V, although this value remains higher than the pacing threshold of the VisionWire. Transcoronary guidewire pacing against the posterior skin patch electrode in combination with the VisionWire yielded the lowest pacing thresholds at 1.0 ± 0.6 V, again lower than the thresholds with the bare floppy guidewire (4.1 ± 3.0 V) and the floppy guidewire/balloon combination (1.6 ± 1.3 V). Within the indifferent cutaneous patch electrodes, the pacing thresholds obtained for the posterior chest wall patch were lower compared to the anterior skin patch electrode for all of the coronary wire variables (Figure 2). The mixed-model statistics showed a significant influence of the guidewires (VisionWire vs. standard floppy guidewire vs. standard floppy guidewire with balloon insulation, p Pacing impedances. The pacing impedances for the different guidewire to skin patch electrode combinations are summarized in Table 2. Using the anterior skin patch electrode, there were only small differences between the VisionWire, the bare floppy-guidewire and the balloon-insulated floppy guidewire despite significantly different pacing thresholds. With the posterior skin patch electrode in use, the impedances for the bare floppy-guidewire were lower compared to the other cathode configurations. Except for the bare floppy guidewire, there were no differences between the two skin patch positions (Figure 3). The mixed model statistics showed a significant influence of the guidewires (p Epicardial R-wave. The magnitude of the transcoronary measured epicardial signal — the R-wave — behaved in a reverse relationship to the pacing thresholds (Table 3; Figure 4). We calculated a significant correlation between the three variables of all data (measurements at 3 vessels, 2 patch electrodes and 3 different guidewire setups) with a correlation coefficient of -0.537 between the pacing threshold and R-wave (p was clearly higher than the R-wave obtained by the bare floppy guidewire at 4.5 ± 2.2 mV. Additional insulation of the floppy guidewire increased the R-wave to 7.5 ± 4.1 mV. R-wave measurement against the posterior skin patch electrode yielded similar results: the maximum R-wave at 10.4 ± 4.3 mV was delivered by the VisionWire, the R-wave form the bare floppy guidewire was lower at 4.9 ± 2.4 mV. Again, after additional insulation of the floppy guidewire with a balloon, the R-wave came up to 8.0 ± 3.9 mV. The position of the skin patch electrode was without influence on the epicardial signal amplitude with a small trend to higher values using the posterior patch electrode. The mixed-model statistics confirmed these observations with a significant influence of the guidewires (p Transvenous pacing. Temporary transvenous pacing was effective in all cases in a unipolar setting (with the tip of the transvenous lead as a cathode against both skin patch electrode configurations. Similarly, the standard bipolar setting (with the tip of the lead set as the cathode in conjunction with the ring electrode as the anode) generated effective pacing. Threshold and impedance data and the endocardial R-wave are summarized in Table 4. Pacing thresholds. Comparable to the coronary pacing approach, the posterior skin patch electrode in combination with the tip of the transvenous lead generated lower unipolar pacing thresholds (0.7 ± 0.3 V) than the anterior skin patch electrode (1.0 ± 0.6 V). The bipolar pacing threshold (0.7 ± 0.3) was as low as the threshold obtained by using the posterior skin patch electrode. Pacing impedances. The unipolar pacing impedances with the posterior skin patch (560 ± 264 ohm) and the anterior skin patch (507 ± 174 ohm) revealed no significant difference and were in the same range as the bipolar pacing impedance (591 ± 233 ohm). Endocardial R-wave. The magnitudes of the endocardial signal measured in a unipolar setting against the different anodal electrodes and in a bipolar setting were similar (Table 4) without significant differences. Complications. No complications of transcoronary pacing could be observed. There was no thrombotic material adherent to the guidewires after removal, nor were intracoronary thrombi seen during coronary angiography. Skeletal muscle contractions at highest output levels disappeared promptly after reduction of pacing amplitude. Despite the extensive pacing protocol no arrhythmias were induced by either transcoronary or transvenous pacing.

Discussion

In the present study, a new guidewire — the VisionWire — was investigated for its suitability in transcoronary pacing. To our knowledge, this is the first application of the VisionWire in transcoronary pacing in an animal model. The VisionWire was developed initially for pacing in the coronary sinus and is delivered with a rather stiff characteristic (extra-support design) for the placement of over-the-wire CS leads for CRT devices.¹⁹ The surface of this wire (except from the proximal and the distal part of the wire) is coated for electrical insulation. For that reason, this wire should be the ideal tool for transcoronary pacing. Pacing threshold and efficacy data from the present study demonstrated the efficacy of the VisionWire in transcoronary pacing. The pacing efficacy using the conventional floppy guidewire without additional insulation was 77% using the anterior skin patch electrode and 87% using the posterior skin patch electrode, thus in the same range as in our clinical study with 85.7% pacing success.⁷ The bare VisionWire produced 100% pacing efficacy in all animals and all vessels attempted, irrespective of the anodal patch position. Using this wire, the pacing thresholds were significantly lower compared to the conventional guidewire. Using the optimal position for the skin patch (the posterior chest wall),¹⁸ the pacing thresholds obtained by the VisionWire were 1.0 ± 0.6 V, thus similar to the current “gold standard” — bipolar transvenous pacing. As expected from the data from our initial animal study,¹⁸ additional insulation of the conventional guidewire by advancing a monorail angioplasty balloon over the wire markedly increased the pacing efficacy to 100%, irrespective of the skin patch location, thus significantly reduced the pacing thresholds further. Irrespective of the setup using a standard coronary guidewire (vis-a-vis skin patch position and balloon insulation use), pacing thresholds with the VisionWire were always lower. These data support the finding from our previously published data¹⁸ that insulation of the distal part of the guidewire is sufficient for improvement of pacing threshold. Mixon et al⁵ reported similar findings of lower pacing thresholds with insulation of the entire guidewire by an over-the-wire-balloon, although they did not investigate the effect on pacing thresholds in a systematic manner. Improving pacing thresholds by insulating the coronary wire with an over-the-wire balloon is of limited practical value because over-the-wire balloons are not usually “workhorse” devices. The data from our animal studies demonstrate the efficacy of “workhorse” monorail balloons in providing sufficient guidewire insulation as illustrated by markedly decreased pacing thresholds compared to the bare guidewire. Thus, monorail and over-the wire balloons are sufficient to generate acceptable pacing data for standard wires in all coronary vessels and in both skin patch positions in this model. Guidewire technology. The new VisionWire with a special coating for electrical insulation does not need additional insulation by an angioplasty balloon to reach low pacing thresholds and a 100% efficacy in transcoronary pacing. From the results of the present study, this guidewire could become the ideal tool for transcoronary pacing. The pacing thresholds obtained by the VisionWire were superior to the thresholds yielded by the standard guidewire with additional balloon insulation. This effect could be attributable to the fact that the monorail balloon covered only the distal part of the guidewire. Whether the small difference between the pacing thresholds between these devices has a clinical impact will need to be elucidated in a clinical trial in humans undergoing coronary interventions. Optimal skin patch position in transcoronary pacing. Because of the significantly higher pacing thresholds using a skin patch in the groin,¹⁸ this patch position was not further investigated in the present study. In comparison to the pacing threshold and efficacy data between the anterior and posterior patch position, the latter yielded the better results irrespective of the setting of the cathode guidewire. To the degree that these data support the findings from our initial animal study,¹⁸ the posterior patch position remains the optimal position for unipolar transcoronary pacing using skin patch electrodes. Furthermore, the excellent pacing thresholds obtained by the posterior skin patch are in contrast to the study from Mixon et al.⁵ These authors found that the pacing threshold using a skin patch electrode was unacceptably high. Unfortunately, there was no information about the position of the skin patch electrode used in their clinical study. Mixon et al⁵ recommended the use of a steel monofilament suture anchored in the subcutaneous tissue as an indifferent electrode. In our opinion, this would increase the risk of bleeding complications and is not required, as our data support the high efficacy of the posterior skin patch adhesive electrode. Finally, the concept of unipolar transvenous pacing using skin patch electrodes was demonstrated in our animal study. The unipolar pacing thresholds using a standard transvenous pacing lead in the right ventricle ranged from 1.0 ± 0.6 V against the anterior skin patch to 0.7 ± 0.3 V against the posterior skin patch, and are thus comparable to the “standard” bipolar setup at 0.7 ± 0.3 V. All these data support our statement that a skin patch electrode is a reliable indifferent electrode for transcoronary pacing if positioned on the posterior chest wall.

Conclusion

The results of the present animal study demonstrate that transcoronary pacing with skin patch electrodes achieves reliable pacing with acceptable thresholds (which are similar to those of transvenous pacing). The technique was used in this study without any identifiable complications. With an optimal pacing setup, there were no significant differences in pacing thresholds between the present “gold standard” (bipolar transvenous pacing) and unipolar transcoronary pacing with a standard PCI guidewire (with balloon insulation) or with the VisionWire against an indifferent skin patch electrode ideally placed on the posterior chest wall. There remain no methodological concerns over the transcoronary pacing concept, particularly given that we achieved 100% pacing efficacy with our model with minimal additional costs (one skin patch electrode) and without additional risks. In unheralded, suddenly occurring episodes of bradycardia during PCI, transcoronary pacing can be initiated within seconds, reducing the risk of hemodynamic instability. However, if the bradycardia persists for several minutes, transvenous pacing should be installed because of the lack of data concerning long-term pacing in the coronary arteries. Transcoronary pacing has been reported to be safe for at least 30 minutes without demonstrable complications.⁵ However, there was thrombus formation reported in an animal model applying transcoronary pacing for several days without sufficient anticoagulation,¹⁷ although this protocol may not be analogous to standard coronary interventional techniques. If this animal data could be reproduced in humans, transcoronary pacing could become the method of choice for the treatment of bradycardias during coronary interventions, especially when using the transradial approach without fast access to a vein suitable for temporary transvenous pacing. Transcoronary pacing can avoid all complications associated with transvenous pacing either prophylactically installed or during resuscitation because of hemodynamically relevant bradycardias. Study limitations. The VisionWire is only certified for transvenous pacing in the coronary sinus. Since this wire is available only in an “extra-support” configuration this would limit its use in coronary interventions, because in most cases floppy or intermediate-tip guidewires (personal experience from the authors) are preferred to avoid damage of the coronary arteries by comparable stiff wires utilized as the “extra-support” wire. In the emergency setting, even if the VisionWire is not suitable as the workhorse wire for the intervention, in the event of an unexpected hemodynamically significant bradycardia, it could be introduced (as a second wire) into any coronary vessel for the sole purpose of initiating pacing. Even if threshold and efficacy data from our animal studies are comparable to the data from our clinical study in patients undergoing coronary intervention, the results of the present animal study cannot be transferred to humans without proof in clinical practice. To investigate this concept, we propose a multicenter study for validation of the new concept of transcoronary pacing (balloon insulation and special coated guidewires) with regard to safety and feasibility in humans. Acknowledgment. The authors wish to thank their colleagues at the IMTR GmbH Rottmersleben for their support in performing this study.

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———————————————————— From Martin-Luther-University Halle-Wittenberg, Department of Medicine III, †IMTR GmbH Rottmersleben, and *Klinikum Merseburg, Department of Medicine I, Merseburg, Germany. This study was supported by a restricted grant from Biotronik (Berlin, Germany). None of the authors has any financial affiliations with this company. Data analysis and interpretation were performed completely independent from this company. Manuscript submitted October 19, 2010, provisional acceptance given November 11, 2010, final version accepted November 29, 2010. Address for correspondence: Roland Prondzinsky, MD, Department of Medicine I, Carl von Basedow Klinikum, Weisse Mauer 52, D-06217 Merseburg, Germany. E-mail: r.prondzinsky@klinikum-merseburg.de