Atrial and ventricular pacing after open heart surgery

Differential relationship between decreased muscle oxygenation and blood pressure recovery during supraventricular and ventricular tachycardia

Vasoconstriction during tachyarrhythmia contributes to maintenance of arterial pressure (AP) by decreasing peripheral blood flow. This cross-sectional observational study aimed to ascertain whether the relationship between peripheral blood flow and AP recovery occurs during both paroxysmal supraventricular (PSVT, n = 19) and ventricular tachycardias (VT, n = 17). Peripheral blood flow was evaluated using forearm tissue oxygen index (TOI), and mean AP (MAP) was measured using a catheter inserted in the brachial or femoral artery during an electrophysiological study. PSVT and VT rapidly decreased MAP with a comparable heart rate (P = 0.194). MAP recovered to the baseline level at 40 s from PSVT onset, but not VT. The forearm TOI decreased during both tachyarrhythmias (P ≤ 0.029). The TOI response was correlated with MAPrecovery (i.e., MAP recovery from the initial rapid decrease) at 20-60 s from PSVT onset (r = -- 0.652 to - 0.814, P ≤ 0.0298); however, this association was not observed during VT. These findings persisted even after excluding patients who had taken vasoactive drugs. Thus, restricting peripheral blood flow was associated with MAP recovery during PSVT, but not VT. This indicates that AP recovery depends on the type of tachyarrhythmia: different cardiac output and/or vasoconstriction ability during tachyarrhythmia.

Use of temporary atrial pacing in management of patients after cardiac surgery

The authors' clinical experience with temporary atrial pacing to evaluate its use in the management of patients after cardiac surgery was reviewed. A total of 339 patients undergoing cardiac surgery were studied with regard to postoperative pacing therapy. Postoperative pacing was performed in 186 of 339 patients to treat supraventricular bradycardia or tachyarrhythmias. Rapid atrial pacing was performed to interrupt re-entrant supraventricular tachyarrhythmias. In bradycardic patients, haemodynamics could be improved as the result of significant increase of blood pressure and oxygen saturation in the pulmonary artery (SVO2) caused by atrial pacing. Premature beats could be suppressed in 63% and supraventricular tachyarrhythmias could be interrupted in 66% of the patients only by atrial pacing. Temporary atrial pacing is safe, rapid and effective as the treatment of choice; it is believed that the technique should be applied in preference to pharmacological treatment in the management of patients after cardiac surgery.

Contribution of atrioventricular synchrony to left ventricular systolic function in a closed-chest canine model of complete heart block: implications for single-chamber rate-variable cardiac pacing

This study assessed the impact of atrioventricular (AV) synchrony on characteristics of left ventricular (LV) systolic function during ventricular pacing over a wide heart rate range in a conscious closed-chest canine model of complete AV block. Ten healthy adult dogs underwent thoracotomy during which complete AV block was created by formaldehyde injection, and paired ultrasonic sonomicrometers were positioned on the LV anterior-posterior minor axis. Following recovery from surgery, peak and end-diastolic LV transmural pressure, maximum dP/dt, stroke work, end-diastolic minor axis dimension, and maximum velocity of shortening, were quantitated at heart rates of 80, 100, 120, 140, and 160 beats per minute (bpm) during both ventricular pacing alone and AV sequential pacing with increasing AV intervals (0, 50, 100, 150, 200, 250, and 300 ms). Over the heart rate range tested, parameters of LV systolic function did not differ significantly during ventricular pacing with or without AV synchrony. For example, during ventricular pacing alone maximum LV dP/dt varied from 2110 +/- 70 mmHg/s to 2463 +/- 567 mmHg/s, a range essentially identical to that observed in the presence of AV synchrony. On the other hand, although the impact on LV performance of varying AV interval from 0 to 300 ms was small, differences tended to become more pronounced at higher pacing rates. At 80 bpm, neither stroke work nor maximum LV dP/dt were affected by change in AV interval, while at heart rates greater than or equal to 120 bpm both stroke work and LV dP/dt tended to maximize at AV intervals of 50 and 100 ms and thereafter declined.(ABSTRACT TRUNCATED AT 250 WORDS)

[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)

Hemodynamic findings during sinus rhythm, atrial and AV sequential pacing compared to ventricular pacing in a dog model

The hemodynamic responses of atrial (AP), atrioventricular sequential (AVP) and ventricular pacing (VP) were compared to sinus rhythm (SR) in seventeen anesthetized dogs with intact AV conduction. The atrium and/or ventricle were paced at fixed rates above the control sinus rate. An AV interval shorter than normal conduction was selected to capture the ventricle. The changes of pulmonary capillary wedge pressure (PCWP, mmHg), mean aortic pressure (MAP, mmHg), cardiac output (CO, L/min), systemic vascular resistance (SVR, dynes/s/cm-5), left ventricular stroke work index (SWI) and mean systolic ejection rate (MSER, ml/s) during sinus rhythm, atrial pacing and atrioventricular sequential pacing (expressed in percentages of the individual values during ventricular pacing) were: (Chart: See text) The importance of atrial systole for cardiac performance was clearly demonstrated in dogs with normally compliant hearts. In both atrial and atrioventricular sequential pacing compared to ventricular pacing there was a reduction of pulmonary capillary wedge pressure (PCWP) (p less than 0.01) and systemic vascular resistance (SVR) (p less than 0.01) despite an increase in cardiac output (CO). The lesser mean systolic ejection rate (MSER) found during atrioventricular sequential pacing compared to sinus rhythm and atrial pacing may be explained by the abnormal ventricular depolarization in this pacing mode; nevertheless, the mean systolic ejection rate was still greater than that found during ventricular pacing (p less than 0.05).

Hypotension with ventricular pacing: an atria vasodepressor reflex in human beings

Hypotension with ventricular pacing has generally been attributed to loss of atrial transport, but it has been suggested that atrial vasodepressor reflexes may play a role. To study this, constant rate atrial and ventricular pacing was performed in 20 supine patients 24 to 36 hours after surgical coronary artery bypass or aortic valve replacement. The pulmonary capillary wedge tracing was examined for the presence or absence of cannon A waves during ventricular pacing in each patient. Thirteen patients had cannon A waves (group I) and seven did not (group II). Ten of the 13 patients with cannon A waves had ventriculoatrial conduction compared with only 2 of 7 patients without cannon A waves. There was a nonsignificant trend toward an association between cannon A waves and ventriculoatrial conduction (p = 0.1). Stroke volume index decreased in both groups when patients were changed from atrial to ventricular pacing. In the patients with cannon A waves, stroke volume index decreased from 31.2 to 26.3 cc/min per m2 (p less than 0.001) and from 31.2 to 25.0 cc/min per m2 (p less than 0.001) in those without cannon A waves (group I versus group II, p = NS). However, mean systemic blood pressure decreased only in patients with cannon A waves (99.4 to 85.9 mm Hg [p less than 0.001] versus 101.8 to 100.9 mm Hg [p = NS]) in those without cannon A waves (group I versus group II, p less than 0.001). Hypotension in patients with cannon A waves was caused by inhibition of the normal reflex increase in systemic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic and symptomatic consequences of ventricular pacing

After implantation of a ventricular demand pacemaker (VVI), occasional patients continue to have dizziness, syncope, or near syncope ("pacemaker syndrome"). To identify patients in whom VVI pacing may have deleterious effects, we compared cuff blood pressure responses to VVI pacing with blood pressure responses to atrioventricular sequential pacing (DVI) or sinus rhythm in 50 consecutive patients. Patients with intact ventriculoatrial conduction had a much greater decrease in systolic blood pressure with VVI pacing (24 +/- 11 mm Hg) than those with ventriculoatrial dissociation (-4 +/- 15 mm Hg) (P less than 0.005). Patients who were in heart failure had a lesser decrease in blood pressure with VVI pacing than did those without failure (P less than 0.05); 13 of the 14 heart failure patients lacked ventriculoatrial conduction. Ten patients had symptomatic dizziness after VVI pacing; the incidence of symptoms was higher in patients with ventriculoatrial conduction (9 of 23) than in those without ventriculoatrial conduction (1 of 27) (P less than 0.003). We conclude that the presence of intact ventriculoatrial conduction appears to be a crucial determinant of the hemodynamic response to VVI pacing, and its presence may identify patients who are at risk for "pacemaker syndrome."

A new orthogonal lead for P synchronous pacing

P synchronous pacing has long been identified as advantageous for patients with atrioventricular conduction defects and intact sinus node function. Prior endocavitary systems have been infrequently employed, because of unreliable P wave sensing from standard ring electrodes in the atrium or the requirement for a second atrial sensing lead. A single endocardial lead employing a unipolar ventricular stimulating electrode and an orthogonal P wave sensing design was developed and tested in 22 patients undergoing electrophysiologic study or pacemaker implantation. Thirteen centimeters from the stimulating tip of a standard permanent pacing lead, three or four electrodes with a surface area of one millimeter squared, equidistant from the tip, were placed circumferentially about the catheter. With the catheter tip normally placed in the right ventricular apex, atrial sensing electrodes were positioned in the mid-high lateral right atrium, adjacent to, but not affixed to, the right atrial wall. Bipolar orthogonal leads X and Y were obtained. In 22 patients, during sinus rhythm, atrial electrogram voltages in the X axis of 2.47 plus or minus 1.6 millivolts and 2.32 plus or minus 1.6 millivolts in the Y axis were recorded. QRS voltages of 0.078 millivolts and 0.073 millivolts, respectively, allowed dramatic ability to discriminate P from QRS complexes (P/QRS equals 32/1). There was no change in QRS or unipolar ventricular pacing. A single catheter designed for P synchronous pacing employing circumferentially placed atrial sensing electrodes has demonstrated unique atrial sensing voltages with excellent QRS signal rejection.

Unfavorable effects of ventricular pacing on myocardial energetics

The effects of ventricular pacing (90-330 beats/min) and atrial pacing (120-210 beats/min) on myocardial oxygen consumption (MVO2) and its hemodynamic determinants and on myocardial pumping efficiency were studied systematically on intact dogs. In six closed-chest experiments 158 steady states were analyzed. Myocardial blood flow was measured with a differential pressure sinus catheter, oxygen consumption (5-30 ml/min . 100g) was determined simultaneously by the Fick principle and the additive hemodynamic parameter Et. Ventricular and atrial pacing were compared with both methods at identical heart rates. Additionally, the coincidence between both methods of determining MVO2 was examined at sinus rhythm with sympathetic stimulation (norepinephrine, atropine) within each experiment. Ventricular pacing increased MVO2 overproportionally up to 50% in relation to the hemodynamic determinants. Consequently, myocardial pumping efficiency markedly decreased with increasing ventricular rate. The close relation between directly measured MVO2 and Et, found in previous studies, was maintained under sympathetic stimulation. Atrial pacing, as compared to ventricular pacing at identical rates, resulted in a decrease of MVO2 up to 25% although the expected mVO2 according to its hemodynamic determinants rather increased. The hemodynamic and metabolic mechanisms probably responsible for the energetic difference between ventricular and atrial pacing at equal heart rates are discussed.

An experimental method for thermal control of heart rate: work in progress

Evaluation of the postoperative course of coronary artery bypass patients shows that a number develop supraventricular arrhythmias that may be responsive to sino-atrial node (SAN) cooling. The sinus rate can be controlled within a clinically useful range with topical cooling probes (thermodes). The data on the variations of heart rate caused by modest nodal hypothermia indicate that a nonpharmacologic clinical system for control of supraventricular tachyarrhythmias is feasible. Prototype thermodes suitable for SAN implantation have been developed.

The influence of left ventricular filling pressure on atrial contribution to cardiac output

The influence of left ventricular filling pressure on the atrial contribution filling pressure and atrial contribution was seen in studies done at baseline (PCW (r=-.53, p less than .025), as well as in studies done after PCW was modified by volume expansion and/or nitrates (r=-.53, p less than .005). At baseline, atrial contribution averaged 9.3 +/- 1.3 c.c./M.2 in patients with PCW less than 20 mm. Hg, while it was only 2.4 +/- 1.2 c.c./M.2 in patients with PCW greater than or equal to 20 mm. Hg (p less than .005). Atrial contribution was significantly greater in patients who had no history of heart failure when they were volume loaded to a PCW above 20 mm. Hg than in patients with impaired ventricular function whose baseline PCW was above 20 mm. Hg. Thus, atrial contribution tends to be less effective in augmenting cardiac output when filling pressure is already elevated, particularly in patients with impaired left ventricular function.