[Determination of thresholds of external cardiac pacing during anesthesia]

Ventricular pacing with a novel gastroesophageal electrode: a comparison with external pacing

Temporary endocardial pacing is a technically demanding invasive procedure requiring sterile precautions and access to fluoroscopy. External (transcutaneous) pacing requires high current for capture and is poorly tolerated in the conscious patient. An esothoracic pacing system has been developed capable of reliable ventricular capture. The flexible gastroesophageal electrode is passed into the stomach. The distal 6 cm is angled to 90 degrees with an internal pulley system, positioning the tip of the gastroesophageal electrode in the fundus of the stomach. Ventricular pacing is performed with a spherical electrode (cathode) mounted on the gastroesophageal electrode tip in conjunction with a chest pad (anode) positioned medial to the cardiac apex. Of 91 subjects in which esothoracic pacing was attempted, 86 (94.5%) demonstrated successful ventricular capture at the maximum pulse duration used (40 msec). Threshold current for ventricular capture ranged from 22.5 +/- 8.1 mA at a pulse duration of 40 msec to 29.9 +/- 8.6 mA at a pulse duration of 10 msec. Esothoracic pacing was compared with external pacing in a subgroup (n = 30) of patients. Ventricular capture with the gastroesophageal electrode was more common when compared with the external approach (27 [90%] of 30 vs 13 [43.3%] of 30, p < 0.001). In those subjects in whom ventricular capture was obtained with both methods, threshold current for capture was significantly lower with the esothoracic approach. This gastroesophageal electrode may be useful in the emergency management of acute bradyarrhythmias.

[Final arrest of a pacemaker after use of electrocautery]

A case is reported of irreversible damage being caused to a permanent programmable pacemaker by electrocautery used in the epigastric region. The pacemaker was rapidly replaced, and the patient had no adverse effects of this accident. The use of monopolar electrocautery in patients who have one of the new generation of programmable pacemakers is very dangerous. Bipolar forceps can reduce the level of interference between electrocautery units and pacemaker electrodes. With programmable pacemakers, the generator instruction manual should be consulted before surgery, as placing a magnet on the generator may not necessarily convert it to the asynchronous mode. When the use of electrocautery is unavoidable, external cardiac pacing electrodes should be placed on the patient, with an external cardiac pacemaker ready.

[Anesthesia and cardiac pacing]

Nowadays, anaesthetists often have to deal with pacemaker patients. All the problems encountered in the anaesthetic management of such patients are discussed in this paper: the pacemaker, specific risks linked to the pacemaker, monitoring of such patients, and temporary pacing. The preoperative assessment of pacemaker function is an absolute necessity. The technical characteristics of the pacemaker can be found in the patient's booklet. The clinical history should reveal a possible malfunction (syncopes). The underlying cardiac disease should be known, as it will have repercussions on the anaesthetic and surgical risks. An electrocardiogram and measurement of blood electrolytes must be carried out. There are three major risks linked to the pacemaker during surgery: 1) the loss of pacing by threshold (drugs, dyskaliemia); threshold (drugs, dyskalemia); 2) ventricular fibrillation (the intracardiac electrode conducting the electrocautery currents); 3) reprogramming or damaging of the pacemaker by electrocautery, cardioversion or nuclear magnetic resonance. The only mandatory monitoring of these patients is the electrocardioscope. Other monitoring techniques will be dictated by the underlying cardiac disease or the surgery planned. Temporary pacing is indicated in the same conditions as permanent pacing. However the intracardiac electrode can be displaced by moving the patient; the efficacy of pacing must therefore be continuously checked. During cardiac surgery, with cardiopulmonary bypass, conduction disturbances can occur. Temporary pacing electrodes should therefore be sewn onto the ventricular epicardium for the duration of the surgery; atrial electrodes should be added if sinus troubles can be expected. Oesophageal pacing is possible in the operating theatre because it is easily and rapidly set up: a bipolar oesophageal electrode linked to an external pacer can speed up the heart (atrial dysfunction) or slow down a tachycardia. An oesophageal electrocardiogram can also be carried out with this electrode. Swan-Ganz catheters can be also used for temporary pacing: either with two pairs of electrodes, atrial and ventricular respectively--this system being useful in a patient who does not move--or with a newer system where a single small electrode is introduced into the right ventricle by a special lumen in the Swan-Ganz catheter. Although external pacing was historically the first technique to be developed, it was abandoned because of the muscle pains it gave. Recently, a new technique of external pacing, with large electrodes and longer stimuli, has been developed for use in emergency situations.(ABSTRACT TRUNCATED AT 400 WORDS)