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Cardiac arrhythmia


Pacemaker insertion

Permanent pacing systems require the implantation of pacing electrodes in contact with the myocardium and the placement of a pulse generator in the body. There are a number of options for accomplishing these tasks. In certain circumstances it may be advisable to implant permanent myocardial electrodes on the surface of the heart at the time of open cardiac surgery. Endocardial contact with the electrode, however, appears to be more satisfactory in achieving long-term, low-threshold function of the electrode. The availability of small-diameter, flexible electrode catheters and small pulse generators makes electrode implantation via the subclavian vein and placement of the pulse generator in the chest wall possible and preferable in nearly every case in both adults and children.

Figure 44-1, A An incision is made on the anterior chest wall below the clavicle. An incision placed on either the right or left side of the chest can be used with equal ease; the choice is based on surgeon preference or patient handedness. Local anesthesia is used. A pocket is formed by separating the subcutaneous tissues from the fascia of the pectoralis major muscle. Hemostasis in the pocket must be meticulous. In children and in some adults with insufficient subcutaneous tissues, the pocket for the pulse generator can be formed beneath the pectoralis major muscle to protect the pulse generator from trauma. General anesthesia is required in these cases. B The superior edge of the incision is retracted to provide access to the first rib–clavicle passageway, beneath which lies the subclavian vein. A needle with a syringe attached is used to locate and penetrate the vein. A flexible J-tip guidewire is passed through the needle into the superior vena cava. The position of the guidewire is confirmed by fluoroscopy. C The needle is withdrawn and replaced with a peel-away catheter sheath. The pacing electrode is passed with ease through the sheath into the superior vena cava. The sheath is then peeled away from the electrode catheter. The electrode is manipulated under fluoroscopic guidance into the right atrial appendage or the apex of the right ventricle, depending on the desired location of cardiac stimulation. When two electrodes are required for atrioventricular sequential pacing, it is usually easier to make separate entry into the subclavian vein rather than attempting to simultaneously place two electrodes through a single catheter sheath. Based on individual patient conditions, a number of tricks for shaping and manipulating the electrode catheter guidewires may be required to reach the desired point in the right heart. A gentle curve anteriorly usually guides the electrode into the right ventricle and out the pulmonary artery. Withdrawal of the electrode allows it to drop into the apex of the right ventricle, where it can be firmly seated with a straight guidewire. A full J-shaped curve of the guidewire allows the electrode to be pulled back into the right atrial appendage. The tines near the tip of the electrode catch in right heart trabeculations to hold its position; generally, however, more secure fixation is desired and is accomplished using a screw-in electrode.

Automatic internal cardioverter defibrillator insertion

Insertion of an automatic internal cardioverter defibrillator (AICD) is also accomplished by electrode implantation using a transvenous technique and subcutaneous implantation of the AICD generator.

Figure 44-2, A An incision is made below the clavicle on the side of the nondominant hand (usually the left side). A subcutaneous pouch may be created if there is sufficient fat to cover the device adequately. Otherwise, the device is implanted beneath the pectoralis major muscle. B The electrodes are implanted via the veins using a needle-catheter technique. The subclavian vein is punctured by a needle, and a guidewire is passed through the needle into the vein. C A catheter sheath is passed over a dilator and the guidewire. The ventricular electrode is passed through the sheath and positioned at the apex of the right ventricle with fluoroscopic guidance. D The simplest AICD configuration uses the ventricular electrode and the generator container as the two electrodes between which the mass of the ventricle is placed to effect cardioversion. In most cases the defibrillation threshold is satisfactory with this simple electrical setup. E Another commonly used configuration employs a second transvenously placed electrode in the superior vena cava. F For patients with previously placed epicardial patch electrodes that are still functional, it may be desirable to use one of these patches in the electrical circuit.

Ventricular tachyarrhythmia

Catheter techniques for the localization and characterization of cardiac arrhythmia precede operation. Most rhythm disturbances can be controlled with properly selected medications. A large number of drugs are available, and new ones are continuously being developed. Should the arrhythmia prove refractory to medical therapy, radiofrequency ablation by intravascular catheter techniques may be indicated. In some cases operation may be indicated when less invasive techniques have failed or in conjunction with other intracardiac operations such as coronary artery bypass, resection of ventricular aneurysm, or cardiac valve reconstruction or replacement.

Figure 44-3, A At operation, the arrhythmia is characterized and localized by a combination of epicardial and endocardial mapping. Epicardial mapping is performed by systematically moving an electrode over the surface of the heart while recording electrocardiograms. A grid is developed from the various electrograms. This technique is essential during operation for Wolff-Parkinson-White syndrome. Only electrograms obtained from the ventricular surface near the atrioventricular groove (shown in larger typeface in the illustration) are important in this syndrome. These electrograms detect early entry of depolarization on the ventricle. Devices that contain multiple electrodes in a net or sock have been developed so that electrograms from multiple points can be obtained simultaneously. The information is analyzed by computer to simplify the process of localizing the focus of the arrhythmia. Endocardial mapping can be performed through a ventriculotomy using either the probe or an electrode placed on a ring. Again, the systematic acquisition of surface electrograms and the development of a grid aid in localizing the focus of the rhythm disturbance. B Operation may be indicated for ventricular tachyarrhythmia refractory to medical therapy or catheter ablation. The location of the irritable myocardium responsible for initiating the rhythm disturbance is usually well known prior to operation because these patients have had multiple catheter studies and multiple attempts to induce and control the problem medically or to ablate the focus of the arrhythmia. Further operative mapping using the surface electrograms directs the surgeon to the areas of the heart most likely to respond to operative intervention. Arrhythmogenic myocardium is usually located at the margin of a myocardial scar, the result of ischemic damage to the heart. Two approaches are commonly used to treat the affected myocardium. The irritable myocardium may be resected by removing a peel of the endocardium, or it may be isolated by an encircling incision on the endocardial surface of the ventricle. C When the focus of the rhythm disturbance is located at the margin of a scar on the anterolateral surface of the left ventricle near the apex, an incision is made into the scar to gain access to the ventricle. Localized endocardial resection of the arrhythmogenic focus is accomplished by dissecting a partial thickness of the ventricular wall. The dissection is started at the margin of the scar and proceeds in a well-developed subendocardial plane of partial scar to normal myocardium. Removal of this portion of the myocardium should eliminate the irritable focus causing the rhythm disturbance. D When the focus of the rhythm disturbance is located on the posterior wall of the left ventricle, a combination of techniques is required to isolate the area. The most complex lesions are those located in proximity to the mitral valve and the posterior papillary muscle. An incision is made through the surface myocardial scar. E The myocardium near the posterior papillary muscle can be isolated by a combination of encircling ventriculotomy and cryoablation. An incision is made in the endocardium and part way through the ventricle wall, around the base of the papillary muscle, and continued to a point near the annulus of the mitral valve. A cryoprobe is used to destroy the myocardium near the mitral annulus. Cryoablation of myocardium is safer and more effective than incision near the mitral annulus and the aortic valve.

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