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a Department of Cardiac Surgery, University Hospital "Vrije Universiteit," Amsterdam, the Netherlands
b Department of Biomaterials, University Medical Centre Groningen, Groningen, the Netherlands
Accepted for publication November 6, 2007.
* Address correspondence to Dr Huybregts, Department of Cardiothoracic Surgery, Vrije Universiteit Medisch Centrum, De Boelelaan 1117, 1007 MB Amsterdam, the Netherlands (Email: majm.huybregts{at}vumc.nl).
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Abstract |
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Description: The atrial cooling device was used in 41 patients undergoing elective coronary artery bypass grafting. Systemic temperatures were held at 36°C, and temperatures of atrial structures were reduced to about 19° to 20°C at 30 minutes.
Evaluation: Electrical activity was effectively suppressed during cross-clamp by controlled cooling of the right atrium. Hemodilution was reduced by right atrial isolation and collection of crystalloid cardioplegia. Cardiac electrical activity returned without sustained arrhythmias in all patients. Postoperative atrial fibrillation developed in only 3 of the 38 patients.
Conclusions: The results indicate that local atrial cooling may contribute to protection of the right atrium, subsequently reducing the incidence of transient postoperative atrial fibrillation.
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Introduction |
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Ischemic injury in the vital conductive tissues of the right atrium has been implicated as a contributing cause of transient postoperative atrial fibrillation [4]. The use of hypothermia is accepted as an important method for preventing ischemic injury of the left ventricle. Currently, no widely accepted methods are used to maintain hypothermia in the conductive tissue in the right atrium. This is surprising, because in the past, atrial fibrillation has been reduced by preventing ischemic injury in the conductive tissues in the right atrium through homogeneous, controlled hypothermia [5].
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Technology |
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A preliminary study in 10 patients demonstrated that the venous cooling cannula could be used safely. The design was slightly modified twice to improve performance. The purpose of this study was to assess the safety, feasibility, and performance of the venous cooling cannula in the clinical setting.
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Technique |
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Device Description
The polyvinylchloride venous cooling cannula (iKool; Edwards Lifesciences Corporation, Irvine, CA) was fashioned into an L shape (Fig 1). At the elbow, a side hole opening existed to collect blood from the superior vena cava. The distal end of the device had a lighthouse tip with openings to collect blood from the inferior vena cava. A polyurethane balloon was located between the two collection openings. Two small caliber tubes were attached to the outer lumen of the cannula, then became integrated into the cannula wall, both ending with the distal openings on the outside of the cannula under the balloon. Luer lock connectors were attached proximally to allow the delivery and withdrawal of cold saline solution into the balloon. Cold sterile saline was circulated through the balloon with an attached closed-loop circuit that included a cardioplegia pump and heat exchanger.
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Patients
Adult patients (aged 18 to 70 years old) with documented right and left coronary artery disease requiring elective, first-time coronary artery bypass graft procedures were entered into the study. Patients were eligible if they had acceptable ventricular function (ejection fraction > 0.25 or equivalent wall motion score) and had normal sinus rhythm, normal atrioventricular conduction time, and normal QRS width. Patients were excluded from participation if they had mitral or tricuspid valve disease greater than class I or a history of atrial arrhythmias.
Intraoperative Procedures
The total priming volume of the heart–lung machine was standard 1400 mL. The iKool was primed during the initial setup of the heart–lung machine. The temperature of the heat exchanger was maintained at 2°C to achieve an inlet saline solution temperature of 4° to 10°C.
Each patient was prepared for the operation by standard procedures. A midline sternotomy was performed, followed by mediastinal tissue preparation for cannulation of the heart. Heparin was injected, and a 24-mm aortic cannula was inserted. Thermal probes were inserted at the intraventricular septum halfway the course of the left anterior descending (LAD) and mid right atrium at the crista terminalis for continuous local temperature measurements. To measure electrical activity during cross-clamping, pace wires were placed on the right atrium and right ventricle and connected to an electrocardiograph (ECG).
A purse string and incision were made 1 to 2 cm above the right atrial/superior vena cava junction, and the iKool was inserted through the superior vena cava, leaving the large bend hole in the superior vena cava, the small side port in the right atrium, and the tip in the inferior vena cava. Proper placement was confirmed by palpation. Extracorporeal circulation was initiated. A 9F aortic root cannula for venting and cardioplegia infusion was inserted. The balloon was inflated by using a syringe with cold sterile saline. The surgeon determined the desired inflation volume of the device by visually confirming occlusion of the right heart inflow and palpating the balloon in the right atrium as well as the termination points of the balloon in both cavae.
After balloon inflation, the aorta was cross-clamped, and antegrade, cold crystalloid, St. Thomas cardioplegia infusion was initiated. After this standard infusion was completed, cardioplegia was partly removed from the right atrium by the small side port of the device. Circulation of the cooling solution commenced at this time. No other methods of hypothermia were used during the procedure, and a normothermic systemic temperature was maintained in the patient.
Immediately before aortic cross-clamp release, the balloon was deflated to allow the heart to fill and to allow right atrial rewarming. The aortic root canula was removed. Cardiopulmonary bypass was stopped after completion of the proximal anastomoses. The iKool was removed, protamine was administered, and the aortic cannula was removed. The surgeon inspected each iKool after its removal from the right atrium. Before the patient left the operating room, the return of cardiac electrical activity without sustained atrial arrhythmias was evaluated.
Postoperative Procedures
Upon admission to the intensive care unit (ICU), cardiac rhythm was continuously monitored. Rhythm strip documentation was collected, and a 12-lead ECG reading was taken every 4 hours and in the event of atrial fibrillation. After transfer from the ICU, patients were continuously monitored by telemetry, and a daily 12-lead ECG was obtained. Patients were followed up until the fourth postoperative day.
Outcome Measures
The safety of the iKool was assessed by evaluating whether the device could be placed correctly and whether the balloon could be inflated and deflated properly without complications. Correct placement of the device was assessed by the surgeon. The ability of the iKool to reduce the temperature of the atrial structures was evaluated through thermal probes during aortic cross-clamping. Suppression of electrical activity during aortic cross-clamping was recorded every 15 minutes during the CABG procedure. The return of cardiac electrical activity without sustained atrial arrhythmias for longer than 15 minutes was evaluated before the patient left the operating room.
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Clinical Experience |
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In another patient, the balloon appeared to have a leak 15 minutes after initiation of cardiopulmonary bypass. The case was completed without balloon cooling. The balloon could not be inflated in 1 patient because of a malformed bond in the balloon. The bonding procedure has since been modified. Manual inflation of the balloon was successfully achieved in all other patients with 37 to 53 mL of saline.
No difficulty in stopping circulation and deflating the balloon was encountered, and the iKool was removed without incident in all patients. All patients were successfully weaned from extracorporeal circulation.
Atrial Structure Temperature Reduction
Atrial and ventricular temperatures dropped during the course of the procedure in all patients. Atrial temperatures were reduced to an average of about 19° to 20°C throughout the procedure (Table 2).
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Cardiac defibrillation during weaning from CPB was required for 12 patients. Before leaving the operating room, all patients had a return of cardiac electrical activity without sustained atrial arrhythmias (>15 minutes), and all patients were in normal sinus rhythm.
Device-Related Complications
No major complications or other organ system events related to the iKool were observed. Backflow through the coronary arteries during distal coronary bypass anastomosis is a common inconvenience in conventional CABG. The device is intended to isolate and separately drain the right atrium, thus minimizing backflow through the coronaries. In this study, backflow was reported as minimal or normal. Only in 2 patients did excessive backflow need to be reduced to minimal by simultaneously venting through the aortic root cannula and the right atrial vent of the iKool. No coronary sinus obstruction was observed. After removal and closure of the superior vena cava cannula insertion site, no bleeding or tearing of tissue was observed. No device-related postoperative bleeding requiring intervention was reported.
Postoperative Incidence of Atrial Fibrillation
Postoperative transient atrial fibrillation developed in 3 patients. One patient converted spontaneously to normal sinus rhythm within 8 hours; the other 2, after increased β-blockers.
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Comment |
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Atrial fibrillation is a significant complication after cardiac surgery that has multiple causes. To reduce postoperative atrial fibrillation, intraoperative recommendations are mild hypothermia, the use of posterior pericardiotomy, and the use of heparin-coated circuits [6].
Myocardial hypothermia is widely accepted for reducing myocardial metabolic needs and ischemic injury [7]. The ideal temperature for protecting right atrial tissue is unknown; however, temperatures below 20°C provide aversion to ischemia in the myocardium [8]. Consistent atrial activity is common during cross-clamp in a conventional cardiopulmonary bypass procedure, and low-voltage ventricular activity is usually seen during the procedure. The sustained electrical silence observed in our study may indicate that controlled, homogeneous hypothermia of the right atrium had affected the electrical system in that area. The low incidence of postoperative atrial fibrillation (3 of 38 patients) may also be a positive indication that the cooling features of the new device may have protected the cardiac electrical system. Another advantage of the iKool is that the removal of crystalloid cardioplegia results in a significant reduction in hemodilution [9] and also decreases detrimental exposure of the myocardium to depolarizing potassium [10].
The study has some limitations. It included a small sample size, and more experience with the device is needed before the full extent of the clinical benefits can be seen. We recognize that the age of the patients, the antiarrhythmic drug regimen, and the lack of patients with a previous incidence of supraventricular arrhythmias in our study represent a limitation in the generalization of our results to a broader population. The adequacy of the myocardial protection technique with this new device needs to be further studied with metabolic or biologic markers.
In summary, the iKool is safe and may contribute to myocardial protection by effectively cooling the conductive tissues of the right atrium. The technology shows a promising outlook for future clinical benefits by offering right heart isolation without the need for vena cavae vessel loops, reducing hemodilution by isolating and removing crystalloid cardioplegia, eliminating volume shifts as a result of rewarming, reducing or eliminating coronary backflow during distal anastomosis, and potentially reducing the incidence of postoperative atrial fibrillation.
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Disclosures and Freedom of Investigation |
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Footnotes |
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