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Ann Thorac Surg 1999;67:36-50
© 1999 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Washington University School of Medicine, St. Louis, Missouri, USA
b Division of Cardiology, Washington University School of Medicine, St. Louis, Missouri, USA
Accepted for publication October 12, 1998.
Address reprint requests to Dr Boineau, Division of Cardiothoracic Surgery, Washington University School of Medicine, 660 S Euclid Ave, Box 8234-3308 CSRB, St. Louis, MO 63110
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Abstract |
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Methods. Ten dogs that had undergone the radial approach (n = 5) or the maze procedure (n = 5) were studied 6 weeks postoperatively. Sinus node function and inducibility of atrial fibrillation were examined before and after operation. The atria were mapped endocardially with 212 electrodes, and atrial activation sequences during sinus rhythm and right atrial pacing were examined. Atrial transport function was assessed by transepicardial Doppler echocardiography.
Results. No dogs developed sinus node dysfunction postoperatively. Both the radial approach and the maze procedure equally prevented sustained atrial fibrillation. The atrial activation sequence was more synchronous after the radial approach than after the maze procedure. There was no electrically isolated region after the radial approach. The total activation time of the left atrium was significantly shorter after the radial approach than after the maze procedure (53.6 ± 9.8 versus 70.5 ± 9.6 ms, p < 0.05). The ratio of peak flow velocity of the E wave to the A wave (peak E/A) of the transmitral Doppler flow was significantly smaller after the radial approach than after the maze procedure (1.7 ± 0.4 versus 3.5 ± 1.7, p < 0.05). The atrial filling fraction of the transmitral Doppler flow was significantly larger after the radial approach than after the maze procedure (29.9% ± 7.3% versus 14.8% ± 5.0%, p < 0.01). There was no significant difference in peak E/A and atrial filling fraction of the transtricuspid Doppler flow between the two procedures.
Conclusions. The radial approach provides a more synchronous activation sequence and atrial transport function, and thus may represent a more physiologic alternative to the maze procedure as a surgical treatment for atrial fibrillation.
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Introduction |
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Material and methods |
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TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
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The surgical technique for the maze procedure was exactly the same as described previously [8]. The atrial incisions of the radial approach have been illustrated in a previous report [7]. The surgical technique is as described herein. Before cannulation, the extracardiac tissue around the superior vena cava and inferior vena cava was dissected. Then, the interatrial groove was dissected. Because there was no incision around the right upper pulmonary vein, the extent of dissection was minimized at this region. Because exposure of the left atrium between the right lower pulmonary vein and inferior vena cava is extremely important in the radial approach, the extracardiac tissue was extensively dissected in this region. The procedures for the right atrium in the radial approach were the same as those for the maze procedure, except for the right atrial appendage incision. In the radial approach, the right atrial appendage was not excised but was incised with at least 2 cm of atrial tissue left between the incision and the sinus node region. The incision was extended anteromedially down to the tricuspid valve annulus 1 cm above the anteroseptal commissure of the tricuspid valve, and in the opposite direction, extended inferiorly toward the lower right atrium with 1 cm of atrial tissue between the intermediate right atrial artery and the incision. Trabeculae in the right atrial appendage were incised and divided to eliminate reentry using the bridging muscles. There were two incisions on the left atrium and interatrial septum in the radial approach. One incision started at the anterior limbus of the fossa ovalis, extended inferoposteriorly, and merged with a lower right atrial incision at the lower posterior septum beneath the right lower pulmonary vein orifice. This incision was further extended toward the inferior left atrium, passing near the right and left lower pulmonary vein orifices, and down to the mitral valve annulus at the commissure between the middle and posteromedial scallops. The coronary sinus was dissected, skeletonized, and cryoablated using a 3-mm cryoprobe (Frigitronics, Inc, Coopersurgical, Shelton, CT) for 2 minutes at a temperature of -60°C. The left atrial appendage was resected. The other incision started at the superior left atrium between the right and left upper pulmonary veins, with 2 cm of atrial tissue left between the right upper pulmonary vein orifice and the incision. This incision was connected to the left atrial appendage excision and extended anteromedially further down to the mitral valve annulus at the anterolateral commissure. Great care was taken to avoid injury to the left circumflex coronary artery during the dissection of the atrioventricular fat pad at this region. To prevent reentry around the right upper pulmonary vein, the atrial tissue between the upper and lower right pulmonary veins was cryoablated. In addition, the atrial tissue between the left atrial incision and each pulmonary vein orifice was also cryoablated to eliminate potential reentry around the pulmonary vein orifice, and conduction block over the incision was ensured by cryoablation at each atrioventricular annulus.
The right atrial incisions were performed while the heart was beating. The aorta was then cross-clamped, and 500 mL of hyperpotassium (26 mEq/L) crystalloid cardioplegic solution (Plegisol; Abbott Laboratories, North Chicago, IL) was infused antegradely through an aortic root cannula. Additional cardioplegic solution (300 mL) was infused 30 minutes later. The left atrial and septal incisions were performed under cardioplegic arrest. A 4-0 polypropylene suture was used to close all atriotomies. After closure of all the left-side incisions, air was removed from the heart, and the heart was reperfused. Ventricular fibrillation was defibrillated by epicardial shocks, if necessary. Dogs were rewarmed and weaned from cardiopulmonary bypass. Protamine sulfate was administered to neutralize heparinization. The chest was closed in layers over a chest tube. The animal was allowed to recover. After no evidence of air leak was confirmed, the chest tube was removed. Postoperatively, supplemental oxygen was given for 6 hours, and buprenorphine (0.01 mg/kg) was also given for pain relief. The dogs received ceftiofur sodium (2 mg/kg) subcutaneously once a day for 3 days postoperatively.
Six weeks after the initial surgical procedure, the dog was transferred from the farm for assessment. The animal was anesthetized, intubated, and ventilated as described earlier. A femoral arterial catheter was inserted to monitor systemic arterial pressure continuously. Arterial blood samples were drawn every 30 minutes to determine arterial oxygen tension, acid–base balance, and electrolyte levels. Ringer’s lactate solution was continuously infused, and sodium bicarbonate, potassium chloride, and calcium chloride were supplemented as indicated to maintain pH and electrolyte levels within normal values. The heart was exposed through a midline thoracotomy and was suspended in a pericardial cradle. After systemic heparinization (3 mg/kg), the inferior vena cava, superior vena cava, and left femoral artery were cannulated, and normothermic cardiopulmonary bypass was instituted. Bilateral ventriculotomies were performed, and the mitral and tricuspid valve leaflets were excised. Two electrode forms carrying 212 unipolar electrodes were inserted into both atria through ventriculotomies across the atrioventricular annuli retrogradely. The electrode forms were made of urethane sponge and were designed to fit the postoperative shape of the canine atrial cavities (Fig 1). The electrodes were custom-manufactured unipolar electrodes, as described previously [9]. The electrode was silver plated and had a diameter of 2 mm. A total of 104 and 108 electrodes were distributed on the right and left atrial electrode forms, respectively. The interelectrode distance ranged from 2 to 5 mm. An indifferent electrode was placed on the chest wall for unipolar reference. After the study, the animal was killed, and the heart was excised with the electrodes in place. The anatomic correlation between each atrial incision and the electrodes was verified in each dog.
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Mapping data acquisition and analysis
A 256-channel mapping system that allowed simultaneous recording of up to 256 signals was used for data acquisition and analysis. The system is based on a Vax/Station II/GPX graphics workstation (Digital Equipment Corp, Maynard, MA) connected to two 128-channel PDP 11/23 Plus-based data acquisition subsystems. The system is run with in-house–developed software (GLAS). Unipolar electrograms were directed to the differential amplifiers with an input impedance of 1012 ohms, and the frequency response was set at 50 to 500 Hz. The input range of the analog-to-digital converter was ±10 V, and an amplifier gain of 250 or 500 was used to generate an input signal range of ±20 mV. Unipolar electrograms as well as the electrocardiogram, pacing artifacts, and reference bipolar right atrial electrograms were digitized at 1,000 Hz with a 12-bit resolution. Data processing was performed at a graphic workstation (IRIS Crimson; Silicon Graphics Inc, Mountain View, CA). Local activation times were determined as the maximal negative derivative of the unipolar electrogram. Activation maps were displayed as dynamic images on a three-dimensional surface model of the canine atria. Location of the atriotomies on the maps was determined by the anatomic correlation between the atriotomies and the electrodes, which was verified in each animal after the experiment. The location was confirmed by the configuration of the electrograms; the electrograms from the electrodes adjacent to the atriotomies frequently showed double or polyphasic potentials. The location and extent of isolation of the posterior left atrium in the maze procedure were also verified by the anatomic correlation between the region and the electrodes. The electrograms recorded at the isolated atrium were usually of low voltage, and the activation times were frequently discordant with the activation times of the surrounding electrodes, suggesting remote activation [10].
To characterize the temporal distribution of atrial activation, the number of electrodes activated during each 10-ms period was represented as a histogram in all dogs. Furthermore, to quantify the atrial activation, total activation time was determined in each atrium from the activation maps during pacing at the right atrium at a paced cycle length of 400 ms. To eliminate the nonspecific delayed activation, the time between the earliest activation and the 95th percentile activation was defined as the total activation time.
Intracardiac pressures and cardiac output
Intracardiac pressures and cardiac output were determined before the initiation of cardiopulmonary bypass. The intracardiac pressure was measured using a fluid-filled catheter (Edwards Swan-Ganz catheter 93A-931H-7.5F; Baxter, Irvine, CA) inserted through the superior vena cava. A 4-0 polypropylene pursestring suture was placed on the superior vena cava 1 cm caudal to the bifurcation of the innominate vein for insertion of the catheter. Systemic blood pressure was obtained from a 16-gauge plastic catheter inserted into the femoral artery. All pressure waves were digitized, recorded, and processed using the previously described system. Systolic, diastolic, end-diastolic, and mean pressures were calculated from the average of five consecutive cardiac cycles.
Cardiac output was measured by the thermodilution method using the same catheter described earlier and a cardiac output computer (COM-1; American Edwards Laboratories, Irvine, CA). A 5-mL bolus of cold (0° to 5°C) saline was injected. The average of three measurements was recorded. Cardiac output was measured during sinus rhythm and during pacing in the right atrium or the right ventricle at the same pacing cycle length (500 ms). All pacing was performed at twice the diastolic pacing threshold. There was a 5-minute interval between the measurements during pacing at different sites. The atrial contribution to cardiac output was determined by the difference between the cardiac output during atrial and ventricular pacing divided by the cardiac output during atrial pacing.
Doppler echocardiography
Transepicardial pulsed Doppler echocardiography (Sonos 1500; Hewlett-Packard, Andover, MA) was performed before the initiation of cardiopulmonary bypass using a 2.5- or 5-MHz imaging transducer. The study was carried out from the apical four-chamber view with the sample volume positioned at the level of the tip of the mitral or the tricuspid valvular leaflets. Subsequently, the sample volume was placed at the entrance of the right superior pulmonary vein to the left atrium. Flow–velocity spectra were recorded on videotape at a display speed of 100 mm/s.
To characterize the transmitral and transtricuspid flow, the peak velocities of the early filling (E) and atrial filling (A) waves and their ratio (peak E/A) were determined. The total diastolic time–velocity integral (TDi) and the time–velocity integral of early ventricular filling (Ei) were measured directly by planimetry of the diastolic mitral and tricuspid flow–velocity spectra. The time–velocity integral of atrial filling (Ai) was calculated as the difference between the integrals ( 
). Each measurement was obtained as an average of three to five cardiac cycles. The atrial filling fraction (AFF), as an expression of atrial transport flow, was then derived as the percentage of the time–velocity integral of atrial filling in relation to the total diastolic time–velocity integral ( 
) [12]. The mitral deceleration time of the E wave was also measured from the transmitral Doppler flow spectra.
From the pulmonary venous flow–velocity spectra, the peak velocities of the systolic (S) and diastolic (D) flow components were obtained. The time–velocity integrals of the systolic (Si) and the diastolic (Di) flow components were also measured by planimetry of the flow–velocity spectra waves. The ratio of the systolic to diastolic peak velocity (S/D) as well as the ratio of the systolic to diastolic time–velocity integral (Si/Di) were determined.
To obtain the average values for these variables in normal dogs, transepicardial Doppler echocardiography was performed in 5 animals through a right thoracotomy preoperatively. Because intraoperative echocardiography during the initial operation significantly increased the incidence of infection and mortality, we did not take the baseline echocardiographic data from all the animals preoperatively.
Weighing of isolated posterior left atrium
After the study, the animal was killed, and the heart was excised. The ventricular myocardium, the great arteries, and the extracardiac tissues were removed from the atria. In the post–maze procedure heart, the electrically isolated part of the posterior left atrium was separated from the remainder of the atria. Both parts of the atria were weighed (Sartorius; Brinkmann Instruments, Inc, Westbury, NY). The percentage of the isolated portion in relation to the entire atria was calculated.
Statistical analysis
Continuous variables are expressed as mean ± standard deviation. Statistical significance of data between the two groups was determined by the Student’s unpaired t test. Comparison of the paired data from the same animal was analyzed by the Student’s paired t test. A value of p < 0.05 was considered statistically significant. Multiple analysis of variance was used to determine the effects of the type of operation and the pacing site on cardiac output.
All animals received humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society of Medical Research and the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Science and published by the National Institutes of Health (NIH publication No. 86-23, revised 1985). In addition, the study protocol was approved by the Washington University Animal Studies Committee.
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Sinus node function
Preoperative sinus cycle length was 542 ± 31 ms after the radial approach and 524 ± 64 ms after the maze procedure. Postoperative sinus cycle length was 578 ± 89 ms after the radial approach and 624 ± 36 ms after the maze procedure. There were no significant differences between the preoperative and postoperative sinus cycle lengths in the radial approach or the maze procedure. No dogs exhibited sinus bradycardia or spontaneous atrial arrhythmias postoperatively. Preoperative maximal SNRT was 674 ± 49 ms in the radial approach and 626 ± 71 ms in the maze procedure. Postoperative maximal SNRT was 704 ± 123 ms after the radial approach and 800 ± 46 ms after the maze procedure. No animals showed prolongation of the maximal SNRT preoperatively or postoperatively.
Inducibility of atrial fibrillation
Preoperatively, sustained AF of at least 10 seconds in duration was inducible in all dogs. The average duration of AF was 57.4 ± 70.7 and 79.4 ± 91.9 seconds in animals undergoing the radial approach and the maze procedure, respectively. There was no statistical difference in the preoperative duration of AF between the two procedures. Both procedures markedly suppressed the duration of AF (Fig 2). Postoperatively, sustained AF was not inducible in any animal. Two animals after the radial approach and 4 after the maze procedure showed brief periods of repetitive atrial responses (up to 10 cycles). The average duration of AF (repetitive atrial responses) was 1.0 ± 1.0 seconds after the radial approach and 0.6 ± 0.9 seconds after the maze procedure. Examples of induction of AF by atrial burst pacing preoperatively and postoperatively are shown in Figure 3. The duration of AF was significantly shorter after than before operation, and there was no statistical difference between the two procedures. Acetylcholine was administered in 3 dogs after the radial approach and in 1 after the maze procedure when no repetitive atrial responses were induced by burst pacing. Acetylcholine provoked the repetitive atrial responses. The induced repetitive responses lasted for 0.2 to 4.8 seconds. Sustained AF was never inducible in any animal.
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Total activation time
Examples of temporal distribution of atrial activation during sinus rhythm in a sham animal and in animals after the procedures are shown in Figure 7 as histograms of the number of electrodes activated during each 10-ms period. In the sham animal, both the right and left atrial activation were distributed over a narrow time range. The right and left atrial-activation completed within 50 and 70 ms after the sinus node activation, respectively. In animals after the radial approach or the maze procedure, the distribution of the right atrial activation was slightly widened and shifted rightward, and the total activation time was prolonged. As confirmed in the activation maps (Figs 4, 5), the left atrial activation started later in the maze procedure than in the radial approach. The distribution of the left atrial activation was widened and the total activation time was slightly prolonged after the radial approach. However, activation at more than 95% of the electrodes in the left atrium was completed within 70 ms (median, 60 ms) after sinus node activation. After the maze procedure, these changes were significantly different. The distribution of the left atrial activation shifted rightward (median, 97 ms), and as a result, the total activation time was prolonged. These patterns of atrial activation distribution were specific to each procedure.
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Transtricuspid flow–velocity
The A wave of the transtricuspid flow was detected in all dogs after both the radial approach and the maze procedure. The peak velocity and the time–velocity integral of the E and A waves across the tricuspid valve and the peak E/A and AFF are shown in Table 4. There was no significant difference between the procedures in any of the variables compared.
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Comment |
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Elimination of atrial fibrillation
The radial approach prevented the induction of sustained AF in canine atria equally as well as the maze procedure. The rationale for operation in AF is that a line of conduction block interrupts the macroreentrant pathway and blocks the fibrillatory wavelets by narrowing the atrial tissue [1]. It is theoretically impossible for the fibrillatory wavelet to reciprocate within atrial tissue in which the circumference is smaller than the wavelength of the wavelet. The radial approach uses the posterior left atrium as a contractile atrial component, resulting in a larger area of atrial tissue in the posterior and superior left atrium to be activated than in the maze procedure. We extended the upper left atrial incision toward the right upper pulmonary vein orifice with approximately 2 cm of atrial tissue left between the end of the incision and the right upper pulmonary vein orifice to minimize the potential for reentry in this region and to allow the activation wavefront to enter the posterior left atrium. Moreover, the tissue between the left atrial incision and the pulmonary vein orifice was cryoablated to eliminate the potential reentrant pathway around one or more pulmonary vein orifices. More recently, microreentry or automatic activity arising from one pulmonary vein orifice has been shown to be a source for AF in certain patients [12]. Therefore, it is strongly recommended that not only the tissue between the incision and the pulmonary vein orifice be cryoablated, but also each pulmonary vein orifice be cryoablated circumferentially to block the activation propagating from the pulmonary vein orifices in patients. In the present study, the radial approach was tested only in AF induced in otherwise normal canine atria. Further study is necessary to confirm that the procedure also prevents AF in enlarged or spontaneously fibrillating atria.
Atrial contribution to ventricular filling
The most important finding in the present study was that the left atrial contribution to ventricular filling was larger in animals after the radial approach than after the maze procedure. The peak E/A was smaller and the AFF was larger in animals after the radial approach than after the maze procedure. The mechanism for this superior atrial mechanical function of the radial approach may be explained by the more physiologic atrial activation sequence. Because the atrial incisions parallel the major directions of activation wavefronts and atrial coronary arteries, the procedure preserves a more synchronized left atrial activation sequence and blood supply to most atrial segments. Moreover, there was no electrically and mechanically isolated or scarred region in animals after the radial approach.
We measured the AFF, as determined by the Doppler flow spectra, as an index of atrial contribution to ventricular filling. Although it is theoretically possible to quantify the relative amount of flow occurring at a given phase in diastole by measuring the flow–velocity integral at the level of the atrioventricular annulus, precise assessment of the flow volume requires accurate measurement of annular area and the assumption that the annular size remains constant, which is not the case. Therefore, we expressed the relative ratio of flow (AFF) rather than actual flow by sampling ventricular inflow at the level of the leaflet tips in this study. The AFF has been shown to quantify the atrial contribution to ventricular filling in normal and diseased hearts [13].
Feinberg and colleagues [3] used Doppler echocardiography to examine atrial function in patients after the maze procedure, 72% of whom were without organic heart disease. They revealed that an A wave was detectable across the mitral valve in 61% of patients, and the mean AFF was 20% in patients with a detectable A wave. Other investigators [4–6] showed that the AFF ranged from 18% to 20% in patients after the modified maze procedure concomitant with mitral valve operation. Atrial function in dogs has not been studied using Doppler echocardiography. The AFF in normal dogs was 33.1% in the present study, a value similar to that in normal human control subjects [3, 13]. The A wave was detectable in 4 of 5 animals after the maze procedure, and the AFF was 14.8% in these animals. Although the AFF after the radial approach (29.9%) was significantly greater than the AFF after the maze procedure in normal dogs, further studies in a long-term model of AF are required.
As shown in Table 3, the significant differences in the peak E/A and the AFF of transmitral flow between the two procedures were brought about by the relatively smaller A waves and larger E waves after the maze procedure than after the radial approach. Similar results have been observed in patients after the maze procedure [4]. The time–velocity integral of the E wave in patients after the maze procedure was larger than that in normal subjects, whereas the A wave was identical, resulting in a smaller AFF in patients after the maze procedure than in normal subjects. Increased flow–velocity and volume during early diastole may be the compensatory process in ventricular filling. Because of a small volume transported into the ventricle during the late filling phase as a result of lesser atrial contraction, the amount of volume transported during early diastole is increased to maintain sufficient ventricular filling, which is the preload for the ventricle to generate cardiac output.
The left atrial contribution to ventricular filling is not only determined by the mechanical left atrial contraction, but is also affected by diastolic function of the left ventricle. In a heart with increased ventricular stiffness, diastolic filling of the ventricle is impaired. Elevated left ventricular end-diastolic pressure diminishes the pressure gradient between the left ventricle and the left atrium, thus impairing passive filling of the ventricle, which occurs in early diastole. Ventricular filling is compensated by atrial contraction in late diastole, leading to a larger A wave, and thus a smaller peak E/A and a larger AFF. Ventricular stiffness can be caused by abnormal myocardial elements with malaligned muscle fibers, increased extracellular components, or interstitial fibrosis [14]. In the present study, the differing ages of the animals or myocardial ischemia during cardioplegic arrest, or both, could have affected the ventricular stiffness. However, the age of the animals ranged from 6 to 13 months in the present study, which excludes the possibility of age-related causes of ventricular stiffness [13]. In addition, the cardiopulmonary bypass and the cardioplegic arrest times were identical between the two procedures. In fact, the mitral deceleration time, which is the best single measurement of chamber stiffness [15], was within the normal range in animals after both procedures. Therefore, a difference in ventricular stiffness may not be the cause of the difference in the peak E/A and AFF between the procedures, suggesting that left atrial mechanical function was better preserved in animals after the radial approach than in animals after the maze procedure.
Although there was a substantial atrial contribution in cardiac output both after the radial approach and the maze procedure, the difference in percent atrial contribution between the two procedures did not reach statistical significance because the right atrial transport function was equally preserved in both procedures, and the left ventricular diastolic function was normal in this model. The difference in the atrial contribution would be significant in patients or animals with impaired left ventricular diastolic function.
Atrial reservoir function
The present study showed that the left atrial reservoir function was reduced after both the radial approach and the maze procedure. The peak velocity and the time–velocity integral of the systolic inflow from the pulmonary veins into the left atrium (S wave) were decreased after the procedures. Similar results have been observed in patients after the maze procedure [3, 5]. Pulmonary venous systolic inflow occurs with atrial relaxation simultaneously with the reduction of left atrial pressure, whereas diastolic inflow occurs with left ventricular relaxation and rapid transmitral filling of the ventricle. Systolic inflow is closely related to left atrial pressure and atrial compliance and has also been shown to correlate with mitral annular motion and mitral valve regurgitation. Diastolic inflow follows the pattern of mitral inflow into the left ventricle. After rapid filling of the left ventricle, left atrial pressure falls below pulmonary venous pressure, and the left atrium fills. During this time, the left atrium acts as a passive conduit between the pulmonary veins and the left ventricle (conduit function). In the present study, the pulmonary capillary wedge pressure was within normal range in all the animals, and no significant mitral valve regurgitation was observed. Therefore, the reduced left atrial reservoir function is believed to be the result of impaired compliance of the atrium. Multiple atrial incisions and subsequent scarring after the procedures could cause restriction of the atrial wall and reduce the compliance. However, despite the decreased reservoir function, atrial transport function at rest was compensated by conduit function and active contractile function in the animals after the radial approach. Further studies are required to determine whether the reduced reservoir function after the radial approach does not affect overall cardiac function, even during exercise.
Prevention of mural thrombus
One of the goals of surgical treatment for AF is to alleviate the risk of systemic thromboembolism by preventing blood stasis in the left atrium, which leads to the development of mural thrombi. Recent studies have revealed that lower blood flow velocity in the left atrial appendage as well as in the posterior left atrium greatly increases the risk of thrombus formation and the incidence of stroke [16, 17]. Although the maze procedure excises the left atrial appendage, which is the most common region for development of mural thrombus, the procedure isolates the posterior left atrium between the pulmonary vein orifices electrically and thus mechanically. The present canine study showed that the isolated posterior left atrium weighed 18.3% of the total chamber after the maze procedure. A previous study [18] using human cadaveric hearts showed that the isolated left atrial block represented 35% of the endocardial surface area of the entire left atrium and 29% of the weight. Even if the remaining atria were in sinus rhythm after the maze procedure, the isolated posterior left atrium would still be fibrillating or inexcitable and flaccid. Therefore, the isolated portion of the left atrium would provide a nidus for the development of mural thrombus and continue to expose patients to the risk of thromboembolism. The radial approach does not create regional isolation in any part of the atrium. Although ultimately it must be determined by long-term observation of patients after operation, the radial approach may reduce the risk of systemic thromboembolism more effectively than the maze procedure.
Surgical technique
Another advantage of the radial approach is that the surgical procedure is technically easier than the maze procedure. The atrial incisions are more linear, and there is no isolation incision or T-shape incision in the left atrium in the radial approach. These incisions make the maze procedure technically difficult. Although the cross-clamp time was similar between the procedures, the number of cryoablations during aortic cross-clamping was seven in the radial approach versus three in the maze procedure. Therefore, if one could use two cryoprobes and ablate two regions simultaneously, one could decrease the aortic cross-clamping time. Exposure of the mitral valve in the radial approach was adequate as well as in the maze procedure. The longitudinal septal incision, extended down to the mitral valve annulus, enables sufficient exposure of the mitral valve. The entire mitral valve leaflets and annulus were visible and accessible in all dogs.
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Acknowledgments |
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We acknowledge the excellent technical assistance of Donna Hand, Gail Moore, Steven Labarbera, Duane Probst, and Dennis Gordon. We also appreciate the assistance of Julio E Pérez, MD, for helpful review of the manuscript, and Dawn Schuessler for preparation of the manuscript.
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