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Ann Thorac Surg 1999;67:1292-1294
© 1999 The Society of Thoracic Surgeons

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Original Articles

Identification of P waves after the Cox-maze procedure: significance of right precordial leads V3R through V6R

^a Deutsches Herzzentrum Berlin, Berlin, Germany

Accepted for publication October 28, 1998.

Address reprint requests to Dr Pasic, Deutsches Herzzentrum Berlin, Klinik für Herz-, Thorax- und Gefäßchirurgie, Augustenburger Platz 1, D-13353 Berlin, Germany
e-mail: pasic{at}dhzb.de

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. The maze circuit lengthens the period of atrial depolarization and may lead to small or absent P waves, which may not be readily apparent in a standard 12-lead electrocardiogram. In this prospective study, we investigate if the right precordial leads V3R through V6R can improve detection of P waves and identification of atrial electrical activity.

Methods. Standard 12-lead electrocardiograms (with leads I through III, aVR, aVL, aVF, and V1 through V6) and right precordial electrocardiograms (V3R through V6R) were recorded in 30 consecutive patients during the first 5 postoperative days and 1, 3, 6, 12, and 24 months after combined Cox-maze III procedure and mitral valve surgery. The P wave identification as an indication of atrial electrical activity and atrial contraction was proved by transesophageal echocardiographic identification of atrial contractions.

Results. Despite echocardiographically identifiable atrial contractions, the P waves were not visible on standard 12-lead electrocardiograms in 7 (23%) patients after 1 and 3 months, and in 4 patients after 6 months. In contrast, right precordial electrocardiograms showed P waves in all of these patients that were best seen in lead V4R. Twelve and 24 months postoperatively, only 2 patients had no visible P waves in the standard leads that were still present in the right precordial leads. However, if P waves were easily identifiable in standard 12-lead electrocardiograms (23 patients at 1 and 3 months after surgery), the right precordial leads showed P waves only in 15 patients.

Conclusions. Right precordial electrocardiogram with leads V3R through V6R is a helpful tool for visualizing P waves after the Cox-maze procedure. Standard 12-lead electrocardiogram should be combined with right precordial electrocardiogram in all patients after the Cox-maze procedure.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
The Cox-maze operation [1, 2] with its current modification [3, 4] is the technique of choice for the management of medically refractory atrial fibrillation [4–6]. In this procedure, multiple atrial incisions are made to channel sinus impulses through a path, or "maze," to reach the atrioventricular node [2, 4]. This prevents a critical mass of contiguous atrial tissue from sustaining atrial fibrillation while maintaining atrial contractility [1, 3]. The maze circuit lengthens the period of atrial depolarization and may lead to small or absent P waves, which may not be readily apparent on telemetry or in standard 12-lead electrocardiogram. During the postoperative surveillance of our patients, we occasionally noted that P waves were visible only in the right precordial leads (V3R through V6R) but not on the standard 12-lead electrocardiograms (leads I through III, aVR, aVL, aVF, and V1 through V6). In this prospective study, we investigated if the right precordial leads V3R through V6R might allow for better detection of P waves and identification of atrial electrical activity.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
Thirty consecutive patients underwent the Cox-maze III procedure [4] concomitantly to mitral valve repair or replacement. Postoperative atrial arrhythmias were treated with antiarrhythmics (digitalis, verapamil). All patients were put on long-term anticoagulation with phenprocoumon (Marcumar) after initial heparin therapy during the first postoperative days.

Standard 12-lead electrocardiograms (with leads I through III, aVR, aVL, aVF, and V1 through V6) and right precordial electrocardiograms (V3R through V6R) were recorded immediately after admission to the intensive care unit, daily, during the first 5 postoperative days, and at 1, 3, 6, 12, and 24 months postoperatively. The diagnostic accuracy of P wave identification in leads V3R through V6R as an indication of atrial electric activity was determined by transesophageal echocardiographic proof of atrial contractions. Transesophageal echocardiographic examinations were performed on the same day as the electrocardiograms were recorded.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Atrial fibrillation disappeared in all patients immediately after surgery. Atrial electromechanical activity appeared in the operating room in 20 (66%) patients, and in 10 patients the sinus node activity was not noted in electrocardiogram, but atrial pacing was possible in all of the patients. Continuous monitoring of the rhythm was necessary because 2 patients with junctional rhythm and atrial pacing were intermittently asystole after temporary stopping of the pacemaker. Episodes of atrial fibrillation were observed in 14 patients during their hospital stay. All of them were treated with digoxin in combination with verapamil, and all patients were in stable sinus rhythm when they were discharged from our institution. Intermittent episodes of atrial fibrillation were observed in 6 (20%) of the patients after the first postoperative month.

During the regular surveillance at 1 and 3 months after surgery, 7 (23%) patients had no visible P waves on standard 12-lead electrocardiograms. However, in all of them, the right precordial electrocardiograms (V3R through V6R) showed P waves that were best seen in lead V4R. Six months after surgery, P waves were not seen in 4 of these 7 patients in standard 12-lead precordial electrocardiograms but were still identifiable in the right precordial leads. Twelve and 24 months after surgery, only 2 patients had no visible P waves in the standard leads, but they were still present in the right precordial lead. However, if P waves were readily identifiable on standard 12-lead electrocardiograms (23 patients at 1- and 3-month examinations), the right precordial leads showed P waves only in 15 patients.

The combination of standard 12-lead electrocardiograms (with leads I through III, aVR, aVL, aVF, and V1 through V6) and right precordial electrocardiograms (V3R through V6R) allowed identification of P waves in all patients with the echocardiographic proof of atrial contractions.

Transesophageal echocardiography showed a different range of atrial contractions in all instances, regardless of whether P waves were identifiable in the right or standard leads, or in both. Echocardiographic findings revealed an atrial (a) wave in Doppler echocardiography and constant atrial contractions of different intensity in echocardiographic color imaging. An improvement of atrial contractility after the maze procedure was documented with the time on close postoperative surveillance. However, there was no echocardiographic difference in atrial contractions regarding P wave identification.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
Our study showed that right precordial electrocardiogram with leads V3R through V6R was a helpful tool for visualizing P waves after the Cox-maze III procedure. Standard 12-lead electrocardiograms (with leads I through III, aVR, aVL, aVF, and V1 through V6) in combination with right precordial electrocardiograms (V3R through V6R) allowed identification of P waves in all patients with the echocardiographical proof of atrial contractions.

After the maze procedure, the main problem in rhythm analysis is whether or not P waves are recognizably present. Normally, atrial depolarization starts at the sinus node and spreads simultaneously in all directions through the myocardium of the right and left atrium. In patients with the maze procedure, multiple atrial incisions made to channel sinus impulses lengthen the period of atrial depolarization. Consecutively, the spread of depolarization within both atria is longer after the maze procedure than usual, which may make for difficult identification of a P wave in the standard 12-lead electrocardiogram. Furthermore, there are several other factors in conjunction with the surgery that may cause this situation, such as the possible alteration of regional architecture after the maze operation, trauma secondary to cardiac surgery causing sinus node dysfunction (such as hemorrhage, ischemia, necrosis, mechanical trauma due to incisions, traction on the heart with retractors and manipulations during the operation, suture injury, placement of caval canullas, damage of the arterial supply of the sinus node), autonomic dysfunction, humoral factors, and cardioactive drugs [7].

In normal individuals, minor alterations of P wave morphologic configuration is common and may reflect variation in sinoatrial and atrial activation with changes in rate, pacemaker site, autonomic tone, or all of these [8]. Furthermore, P waves may not be visible because they are not present, such as in cases of sinus arrest, sinoatrial block, and atrial flutter or fibrillation. In some instances, P waves may not be seen, although present, because they are obscured for technical reasons such as poor recording, suboptimal choice of recording lead, or in the case of low voltage P waves such as in pericardial effusion or in obese subjects. The third possibility is that P waves, although present, may not be visible because they are obscured by another part of the electrocardiogram, such as hidden in the QRS, S-T segment, or T wave.

It should be emphasized that having a P wave does not prove sinus node function and also does not necessarily prove mechanical function of the atria. Atrial contractions are markedly altered after the Cox-maze procedure for a number of different reasons, including altered electrophysiology and altered atrial contractility. Pacemaker activity with a consecutive P wave may occur not only from the sinus node but also from any other ectopic site located in parts of the atria, the coronary sinus, the AV nodal (junctional) area, the His bundle, the bundle branches, or the Purkinje network. Such sites may take over the pacing function from the sinus node due to modulation of normal pacemaker activity by neuro-humoral autonomic influences and depressed activity of the sinus node. These slight morphologic abnormalities such as a low right atrial pacemaker cannot be easily recognized, causing P waves that may also be difficult to observe. This process may be further attenuated after the Cox-maze procedure.

In our patients with echocardiographically identifiable atrial contractions, P waves were always seen in the right precordial electrocardiograms if P waves were not visible in the standard 12-lead electrocardiograms. We concluded that the right precordial electrocardiogram (V3R through V6R) is simple, readily available, and an objective tool for visualizing P waves in patients with echocardiographically identifiable atrial contractions but not readily apparent P waves in the standard 12-lead electrocardiogram. Therefore, standard 12-lead electrocardiograms should be combined with right precordial electrocardiograms in all patients after the Cox-maze procedure to improve detection of P waves and identification of atrial electrical activity.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

1. Cox J.L., Schuessler R.B., D’Agostino H.J., Jr, et al. The surgical treatment of atrial fibrillation. III. Development of a definitive surgical procedure. J Thorac Cardiovasc Surg 1991;101:569-583.[Abstract]
2. Cox J.L. The surgical treatment of atrial fibrillation. IV. Surgical technique. J Thorac Cardiovasc Surg 1991;101:584-592.[Abstract]
3. Cox J.L., Boineau J.P., Schuessler R.B., Jaquiss R.D.B., Lappas D.G. Modification of the maze procedure for atrial flutter and atrial fibrillation. I. Rationale and surgical results. J Thorac Cardiovasc Surg 1995;110:473-484.[Abstract/Free Full Text]
4. Cox J.L., Jaquiss R.D.B., Schuessler R.B., Boineau J.P. Modification of the maze procedure for atrial flutter and atrial fibrillation. II. Surgical technique of the maze III procedure. J Thorac Cardiovasc Surg 1995;110:485-495.[Abstract/Free Full Text]
5. McCarthy P.M., Castle L.W., Maloney J.D., et al. Initial experience with the maze procedure for atrial fibrillation. J Thorac Cardiovasc Surg 1993;105:1077-1087.[Abstract]
6. Kosakai Y., Kawaguchi A.T., Isobe F., et al. Modified maze procedure for patients with atrial fibrillation undergoing simultaneous open heart surgery. Circulation 1995;92(suppl II):359-364.[Abstract/Free Full Text]
7. Pasic M., Musci M., Siniawski H., Edelmann B., Teodoriya T., Hetzer R. Transient sinus node dysfunction after the Cox-maze III procedure in patients with organic heart disease and chronic fixed atrial fibrillation. J Am Coll Cardiol 1998;32:1040-1047.[Abstract/Free Full Text]
8. Boineau J.P., Canavan T.E., Schuessler R.B., et al. Demonstration of a widely distributed atrial pacemaker complex in the human heart. Circulation 1988;77:1221-1237.[Abstract/Free Full Text]

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