FOR SOME PATIENTS WITH atrial fibrillation (AF) and no coronary artery or valvular heart disease, a minimally invasive cauterization procedure called Mini-Maze is showing promise for curing the dysrhythmia without the need for sternotomy or cardiopulmonary bypass.
The Mini-Maze is based on the Maze procedure, which is open-heart surgery involving multiple carefully placed incisions in the left atrium. These incisions are sewn back together, generating mazelike scar tissue that force aberrant electrical signals to follow a more direct path to the ventricles. Another Maze version involved ablating tissue around the four pulmonary veins. Because of the open sternotomy, the surgeon doing a Maze procedure could also perform coronary artery bypass grafting or valve surgery if necessary.
In contrast, the Mini-Maze procedure, which is performed thoracoscopically, focuses on ablating the ganglia surrounding the pulmonary veins and the ligament of Marshall (a remnant from fetal development believed to initiate adrenergic atrial tachycardia that can lead to AF). The left atrial appendage also is excised or stapled. Patients who undergo this less invasive procedure have expected hospital stays of 1 to 2 days, compared with 3 to 5 days for open cardiac surgery.
The procedure is indicated for patients with symptomatic paroxysmal AF that can't be controlled by medical therapy. Patients who've had previous heart surgery may not be candidates because pericardial scarring and lung adhesions can make it difficult or impossible to perform the Mini-Maze procedure thoracoscopically.
Before the procedure, the surgeon will obtain the patient's informed consent. Potential risks of the Mini-Maze procedure include infection, bleeding, and embolism leading to stroke or myocardial infarction. Like all cardiac surgeries, the Mini-Maze procedure poses the risk of heart failure and fluid overload. Rarely, an open sternotomy is needed if the thoracoscopic approach can't be done—for example, because of adhesions. The surgeon should discuss this possibility with the patient before surgery and obtain consent for an open procedure if he discovers during surgery that the thoracoscopic approach isn't possible.
Preoperative testing includes a stress test to assess coronary artery blood flow. Some surgeons require a two-dimensional echocardiogram to determine left atrial chamber size and to look for a clot in the left atrial appendage. To map atrial structures and valves, the surgeon also may order computed tomographic coronary angiography to evaluate the left atrium and pulmonary veins, especially if the patient has had right-sided heart catheter ablation.
Routine preoperative testing for cardiac surgery includes a complete blood cell count, complete metabolic panel, ECG, chest X-ray, urinalysis, and type and cross-match for packed red blood cells.
Depending on the facility and physician preference, the patient may be asked to stop taking anticoagulants and antiplatelet medications at least 1 week before surgery. To reduce the risk of emboli during this time, the patient may be given low-molecular-weight heparin or unfractionated heparin for 4 to 5 days before surgery. He'll also wear antiembolic stockings or have sequential compression devices on his legs preoperatively and during the procedure.
To reduce the risk of infection, have the patient shower with an antibacterial soap the night before surgery and clean the chest walls with antibacterial cloths on the night before and morning of surgery.
The Mini-Maze procedure in brief
The 3- to 4-hour long procedure is performed in the OR with the patient endotracheally intubated and under general anesthesia. With the patient positioned on his left side, the surgeon makes three small incisions in the chest—one for the ablation device, one for the endoscope, and one for surgical instruments. He opens the pericardium above the phrenic nerve and dissects the areas surrounding the right pulmonary veins. By isolating and ablating the tissue surrounding the veins, he interrupts the abnormal circuits that trigger the dysrhythmia. (He leaves the right-sided atrial appendage intact because it produces atrial natriuretic peptides that reduce peripheral edema.)
After the patient is repositioned on his right side, the surgeon isolates and ablates tissue surrounding the left pulmonary veins. He also ablates selected left atrial autonomic ganglionated plexuses, which are nests of nerve cells on the surface of the atrium that can send out electrical impulses. He staples or excises the useless left atrial appendage—a major source of clot formation—and ablates the ligament of Marshall.
Postprocedure nursing care
Although most patients will be in normal sinus rhythm after the Mini-Maze procedure, some may still revert to AF while the scars on the peripulmonary vein tissues are developing. Another reason for temporary postoperative AF is that atrial tissue becomes edematous after the procedure, shortening the cells' refractory periods. This postoperative condition makes it easier for an irregular beat to trigger AF, so monitor the patient closely. Fortunately, postprocedure AF generally responds to medical therapy with beta-blockers, calcium channel blockers, and warfarin if indicated.
Postprocedure hypokalemia and hypomagnesemia also can trigger AF, so closely monitor the patient's serum potassium and magnesium levels and administer potassium or magnesium replacement as prescribed. Keep the patient's potassium level above 4 mEq/L and magnesium level between 2 and 2.2 mg/dL.
Because of the high risk of postprocedure pericarditis, the surgeon may prescribe tapering doses of steroids for 10 to 12 days. Monitor the patient for increased sedimentation rate, fever, chest pain, and leukocytosis, which can indicate pericarditis. You also may note pleuric pain referred to the shoulder or trapezius muscle, ST-segment elevation, or PR-segment depression. A pericardial friction rub confirms the diagnosis of pericarditis.
Small-bore chest tubes or drainage tubes, generally inserted bilaterally during the procedure, are removed in 1 to 2 days, once drainage is less than 100 mL in 24 hours. Antibiotics aren't routinely prescribed (but if you see signs and symptoms of infection, such as purulent drainage, obtain a specimen for culture and sensitivity testing and notify the healthcare provider).
To manage postoperative pain, the patient will have I.V. analgesia such as morphine or hydromorphone, typically given via patient-controlled analgesia pump. Once normal active bowel sounds return and the patient can eat and drink, he'll be switched to oral medication, such as acetaminophen with hydrocodone. Administer an oral analgesic 30 to 60 minutes before ambulation. Encourage early aggressive ambulation to reduce the risks of prolonged bed rest, which include venous thromboembolism and pressure ulcers.
In about 6% of patients, underlying sick sinus syndrome, atrioventricular block, or symptomatic bradycardia means the patient may need an implanted pacemaker postoperatively.
A potential postoperative complication is temporary phrenic nerve paralysis and shortness of breath caused by the trocar used for the thoracoscopic procedure. (The sixth or seventh intercostal spaces, where the trocar usually is introduced, are close to the phrenic nerve.) This paralysis, while annoying, usually resolves over a few weeks to a few months.
Your patient will probably be discharged home within a day or two after the procedure. Teach him about his medications, including analgesics, antiarrhythmics, and anticoagulants. Explain dietary restrictions he must follow while taking anticoagulants, and enroll him in a warfarin clinic to monitor his blood levels. Teach him about wound care and tell him to report signs and symptoms of infection such as fever, drainage, redness, increasing pain, and swelling at the incisional site.
Your patient will take antiarrhythmic and anticoagulant medications for at least 6 months postoperatively. During this time, he'll be monitored closely for reemergence of the AF, with a spot 12-lead ECG done at 3 weeks and 3 months postoperatively. Tell him to keep a log of any symptoms such as palpitations or irregular pulse and to document what he was doing at the time and how long his symptoms lasted. If the symptoms don't resolve or he develops AF with a rapid ventricular rate, he should seek emergency medical treatment.
At the 6-month follow-up visit, he'll be asked to wear a 7-day continuous loop heart monitor to detect any evidence of AF, which can be asymptomatic in some patients. Because the Mini-Maze procedure is relatively new, he'll need continuous loop heart monitoring every 3 to 6 months for 5 years to assess continued sinus rhythm. (If he has a pacemaker that continuously records rhythm, the cardiologist can just interrogate his pacemaker to elicit the recorded rhythms for the past several months.)
If the 6- and 12-month visits show no incidence of AF, the antiarrhythmic may be discontinued; after 18 months, anticoagulation can be weaned. If the 6-month visit shows isolated paroxysmal episodes of AF, the patient will remain on an antiarrhythmic and anticoagulation and return to the clinic at 9 months postoperative to be reassessed.
Occasionally, a patient's AF or atrial flutter persists because the foci are in the ganglionic plexuses in the right atrium. In this case, the patient would return to the hospital, where the cardiologist can ablate these tissues via femoral venous access. This procedure should be done at least 3 to 6 months after the Mini-Maze, to give cardiac tissues time to heal. Electrical cardioversion may be performed concurrently with the ablation. The patient will need bridging with anticoagulation therapy with a documented therapeutic international normalized ratio for 3 to 4 weeks before a second ablation can be performed.
The Mini-Maze procedure has successfully been used to treat AF in hundreds of patients. By understanding the different treatments available to the patient and the risks and benefits of each, you can help your patient make an informed decision about his care and guide him through the Mini-Maze.
Barnett SD, Ad N. Surgical ablation as treatment for the elimination of atrial fibrillation: A meta-analysis. J Thorac Cardiovasc Surg.
Gillinov AM, McCarthy PM, Blackstone EH, et al. Surgical ablation of atrial fibrillation with bipolar radiofrequency as the primary modality. J Thorac Cardiovasc Surg.
Minimally Invasive Surgery for Atrial Fibrillation.http://www.minimaze.org/minimazesurgery.htm