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Ann Thorac Surg 2006;82:2292-2294
© 2006 The Society of Thoracic Surgeons
a Department of Surgery, Columbia University, College of Physicians and Surgeons, New York, New York
b Department of Biomedical Engineering, Columbia University, College of Physicians and Surgeons, New York, New York
c Department of Pediatrics, Columbia University, College of Physicians and Surgeons, New York, New York
Accepted for publication April 27, 2006.
* Address correspondence to Dr Spotnitz, Department of Surgery, Columbia College of Physicians and Surgeons, 622 W 168th St, New York, NY 10032. (Email: hms2{at}columbia.edu).
| Abstract |
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| Introduction |
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A 71-year-old man with dilated cardiomyopathy and class IV congestive heart failure was referred for Staphylococcus epidermidis bacteremia. Transesophageal echocardiography revealed a mobile, 15-mm echodensity on the right atrial lead of a dual chamber pacemaker/implantable cardioverter defibrillator (ICD) system. The QRS duration was 220 ms on electrocardiogram. Ejection fraction was estimated at 15% with moderate mitral regurgitation and dyssynchrony of contraction between the interventricular septum and left ventricular free wall.
The patient underwent a median sternotomy with extraction of endocardial pacemaker/ICD leads on cardiopulmonary bypass and removal of the ICD generator. In anticipation of permanent BiVP, temporary BiVP was tested before cardiopulmonary bypass. Mapping of the LV was performed using an aortic flow probe, a multi-electrode patch, and a randomized protocol to identify the optimal lead position and right ventricleleft ventricle delay (RLD) [12]. Permanent LV epicardial leads were implanted at the conclusion of the procedure, and temporary leads were used for perioperative BiVP.
Informed consent was obtained by an approved protocol of the institutional review board. The chest was entered through a standard midline sternotomy and a pericardial well was created. The pericardial space was free of adhesions with clear fluid. During anticoagulation, cannulation, and excision of the ICD generator and leads from the chest wall, temporary pacing was established through the right atrial appendage and anterior right ventricle (RV). An epicardial pacing patch incorporating six bipolar pacing leads was placed behind the posterolateral LV and was connected to a temporary pacing unit containing a Medtronic InSync III pacemaker (Medtronic Inc, Minneapolis, MN). A 90-mm electromagnetic flow probe (Carolina Medical Inc, King, NC) was placed around the ascending aorta. Dual chamber mode BiVP was initiated at a heart rate of 90 and an atrioventricular delay of 150 ms. Fifty-four combinations of nine RLDs and six LV sites were tested at 15-second consecutive intervals in a randomized sequence. The LV sites were apex, inferomedial, inferolateral, posterior descending artery, circumflex, and obtuse margin. The RLDs covered a range from 80 ms (right ventricle first pacing) to 80 ms (LV first pacing) in 20 ms increments.
Analog data for electrocardiogram, arterial blood pressure, and aortic flow velocity (Fig 1) were acquired and transferred through a 16 channel analog to digital converter (MacLab, ADInstruments Inc, Milford, MA) to a personal computer (iMac, Apple Computer, Cupertino, CA). Data were then imported into Matlab (The MathWorks, Inc, Natick, MA). Using customized routines, a relatively small number of arrhythmic beats were eliminated. Aortic flow velocity was integrated over each 15-second interval to give cardiac output and was divided by body surface area to give cardiac index. Results were plotted using response surface methodology producing a two-dimensional plot in which percentage change in cardiac index was indicated by color.
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Biventricular pacing was objectively compared with no pacing on several occasions. On the first postoperative day, cardiac index increased 13% with BiVP. At the time of permanent pacemaker/ICD implantation, initiation of BiVP immediately increased radial artery systolic pressure from 104 to 148 mm Hg. The patient was discharged from the hospital after completion of antibiotic therapy and implantation of a new pacemaker/ICD with BiVP capability.
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The surgical procedure described in this report allowed BiVP optimization under an approved protocol of the institutional review board. The effect of posterior, inferior, and lateral LV pacing as well as timing were defined, and a distinct effect of both LV site and RLD on cardiac index was demonstrated.
The hemodynamic benefits of BiVP in this patient were particularly profound. Biventricular pacing is more likely to be effective as ejection fraction decreases and as intraventricular conduction delay, LV dyssynchrony, and mitral regurgitation increase [10]. Our patients cardiomyopathy was relatively advanced in all of these respects. The precise mechanism of benefit in this patient may include restoration of synchronous contraction of the free wall and septum, reduction of mitral regurgitation, or both. Most importantly, we do not know whether the profound benefit experienced by this patient reflects the advanced nature of his cardiomyopathy or mapping of the optimal site-timing relation. However, it is clear that additional studies in this area are needed and that the question of how to best optimize clinical results of BiVP may need further attention.
Despite limitations, this is the first clinical report of the relative importance of site and timing in BiVP. Results indicate that BiVP optimization can increase cardiac output by 66% when best and worst pacing protocols are compared and provide a rational basis for additional studies aimed at maximizing the clinical response to pacing for heart failure.
| Acknowledgments |
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