A critical look at temporary ventricular pacing following cardiac surgery.

The effect of atrial, ventricular, and atrioventricular (A-V) sequential pacing on cardiac output (CO) was evaluated in patients within 24 hours after cardiac surgery. In patients with normal sinus rhythm, ventricular pacing reduced CO by as much as 42% (average, 14%), whereas atrial and A-V sequential pacing at the same rate increased CO by averages of 13% and 19%, respectively. In patients with junctional rhythm, increase of the heart rate by ventricular pacing produced an increase in CO, however, and an additional 25% increase in CO could be obtained by atrial or A-V sequential pacing at the same rate. Atrial or A-V sequential pacing was superior to ventricular pacing at the same rate and they are the preferred methods for temporary carciac pacing in the postoperative period. In suitable cases elective A-V sequential pacing is an effective method for increasing CO after cardiac surgery.     

Is use of temporary pacing wires following coronary bypass surgery really necessary?

AIM: Temporary epicardial pacing wires (TEPW) which are routinely used after coronary bypass grafting may result in significant complications. We sought to identify variables that predict TEPW implantation and thereby limit their use. METHODS: This prospective study enrolled 564 patients (296 underwent coronary artery bypass grafting with cardiopulmonary bypass [ONCAB] and 268 underwent off-pump coronary artery bypass grafting, OPCAB). TEPW were placed in patients with the intraoperative presence of one or more of the following criteria: sinus bradycardia, sinus arrest, nodal/junctional rhythms, atrioventricular block, bundle branch block, ventricular tachycardia, or onset of atrial fibrillation. RESULTS: Only 31 (5.5%) patients [ONCAB: 20 (6.8%) (ventricular: 14, bichamber: 6); OPCAB: 11 (4.1%) (ventricular: 9, bichamber: 2)] had temporary epicardial pacing wires implanted intraoperatively. Indications for using temporary epicardial pacing wires for ONCAB were sinus bradycardia (8), nodal/junctional rhythms (3), atrioventricular block (3), atrial fibrillation (4), and bundle branch block (2), and for OPCAB were sinus bradycardia (8), nodal/junctional rhythms (2), and atrioventricular block (1). Mean duration for pacing was 22.4 h for the ONCAB group and 11.3 h for the OPCAB group. There were no temporary epicardial pacing wires associated complications. One paced OPCAB patient required a permanent pacemaker and 2 non-paced OPCAB patients required transvenous pacing wires. Univariate and multivariate analyses were also conducted to determine risk factors for TEPW. CONCLUSION: TEPW implantation is overused in cardiac surgery and by identifying independent predictors for pacing we conclude that TEPW use should be limited to a select few.     

Temporary transmyocardial pacing using epicardial pacing wires and pacing pulmonary artery catheters

This study investigated the feasibility of transmyocardially pacing the heart using one temporary epicardial pacing lead and one endocardial lead of a pacing pulmonary artery catheter. Twenty patients undergoing cardiopulmonary bypass with cardioplegic arrest were studied 10 to 45 minutes and 18 to 30 hours after discontinuation of cardiopulmonary bypass. The Swan-Ganz Flow-Directed Pacing TD Catheter (Baxter Healthcare Corporation) was inserted in one group of 10 patients, and the Swan-Ganz Thermodilution A-V Paceport Catheter (Baxter Healthcare Corporation, Irvine, CA) was used in another group of 10 patients. Using the Pacing TD Catheter, transmyocardial atrial (TMA) pacing was successful in 14 of 16 attempts (87.5%), and transmyocardial ventricular (TMV) pacing was successful in 15 of 16 attempts (93.8%). With the AV Paceport Catheter, TMA pacing was successful in 16 of 18 attempts (88.9%), and TMV pacing was successful in 17 of 19 attempts (89.5%). Transmyocardial atrial-ventricular sequential pacing was achieved in all cases when both TMA and TMV pacing were independently successful. There were no significant differences between catheters in the success rates of either TMA or TMV. It is concluded that transmyocardial pacing is feasible using one temporary epicardial pacing lead and one endocardial lead of a pacing pulmonary artery catheter.     

Permanent cardiac pacing after the Fontan procedure

Permanent cardiac pacing after a Fontan procedure is complicated by complex cardiovascular anatomy. Of 332 patients undergoing the Fontan procedure at the Mayo Clinic, we evaluated 15 who postoperatively required permanent pacing (mean age 16.5 years, range 4 to 31 years). Underlying congenital cardiac defects included univentricular heart in nine patients, double-outlet right ventricle in three, and tricuspid atresia in three. The indication for pacing was postoperative heart block in seven patients, congenital heart block in five, postoperative sick sinus syndrome in two, and heart block because of previous operation in one. Pacemakers were implanted immediately postoperatively in 11 patients and 12 to 57 months later in four patients. VVI systems were used in nine patients, DDD in four, AAI in one, and a Medtronic Activitrax VVI in one. All ventricular leads were epicardial. Four atrial leads were transvenous endocardial and one was epicardial. Three patients died 4, 9, and 69 months later of causes unrelated to pacing. Among the 12 survivors, mean follow-up was 34 months (range 1 to 107 months). Two patients had a total of three episodes of loss of ventricular capture because of increased chronic thresholds. Our current approach to pacing after a Fontan procedure includes (1) intraoperative placement of temporary atrial and ventricular electrodes, (2) intraoperative attachment of a permanent ventricular epicardial lead for congenital or surgically induced high-grade atrioventricular block, (3) postoperative insertion of transvenous atrial leads if dual-chamber pacing is indicated, and (4) use of programmable pulse generators with high output capability.     

Atrial and ventricular pacing after open heart surgery

The effect of cardiac pacing, through a wide range of pacing rates, has been studied in 13 patients in stable sinus rhythm within 24 hours of operation. Using first atrial and then ventricular pacing, the cardiac rate was raised to 60% above control value. The effects of atrial and ventricular pacing were compared by observing the differences in the various parameters measured at corresponding paced heart rates. With atrial pacing there was no significant difference in the cardiac output, mean aortic pressure, mean left atrial pressure, or left ventricular work. During ventricular pacing there were significant falls in cardiac output (p<0·05), mean aortic pressure (p<0·01), and left ventricular work (p<0·01). There was a significant rise in mean left atrial pressure (p<0·01).In this study atrial pacing had no significant effect on the parameters measured, through a wide range of cardiac rates. An inotropic effect resulting from increase of rate was not seen. Reported increases in cardiac output following pacing must therefore have resulted from correction of a dysrhythmia. Ventricular pacing incurs a definite haemodynamic penalty if used in patients with an intact atrioventricular conducting pathway. If atrial pacing is not available, this penalty must be balanced against the possible haemodynamic advantage of suppressing a dysrhythmia.     

Temporary external DDD pacing after cardiac operations

Temporary atrial and ventricular pacing in the DVI, VVI, and AOO modes using atrioventricular sequential DVI devices is routinely used in cardiac operations. This study evaluated a new temporary external DDD pacemaker (Medtronic 5345 External Pulse Generator) capable of ten pacing modes. Thirty-nine devices have been applied to 38 adult patients (27 male, 11 female) after a variety of open heart procedures. Group 1 had atrial pacing wires placed 1.5 to 2.0 cm apart superiorly on the right atrium, group 2 had atrial wires placed 1.0 to 1.5 cm apart on the right atrial free wall, and group 3 had atrial wires placed on the right atrial free wall 0.8 cm apart, using a Silastic ring for fixation. Ventricular wires were placed on the free wall (group 1) or the diaphragmatic surface (groups 2 and 3) of the right ventricle. Postoperative atrial and ventricular sensing and pacing thresholds were obtained on return to the intensive care unit; analysis of variance demonstrated a significantly greater atrial sensing threshold in group 3. Four patients in group 1 permanently lost atrial sensing, 1 patient in group 2 intermittently lost atrial sensing at 24 hours with return at 36 hours postoperatively, and 1 patient in group 1 lost ventricular sensing capability. All other patients had adequate atrial and ventricular sensing capability documented until elective pacemaker removal (mean, 166 hours; range, 17 to 667.5 hours). Nineteen patients required some form of temporary pacing postoperatively; 11 patients demonstrated hemodynamic benefit from a pacing mode that is not available on the currently used DVI devices, and 7 of these required true DDD pacing capability. Six patients benefited from atrial pacing with adequate atrial sensing and simultaneous ventricular backup. Burst pacing with the device was used successfully to treat postoperative atrial flutter in 2 patients. We conclude that temporary external DDD pacing is feasible and effective in postoperative cardiac surgical patients. Atrial sensing is possible in most patients but electrode positioning is important for adequate thresholds. In some patients, hemodynamic as well as electrophysiologic improvement can be demonstrated with universal DDD pacing capability as compared with standard DVI pacing.     

Influence of cardiac pacing on graft flow following aortocoronary bypass surgery--comparison of ventricular and atrial pacing

To evaluate the influence of cardiac pacing on hemodynamics and graft flow dynamics following aortocoronary bypass surgery, we measured vein graft flow, systolic and diastolic graft flow volume along with blood pressure and cardiac output during atrial and ventricular pacing in 20 patients, 26 grafts. During ventricular pacing, systolic blood pressure showed a significant decline of 17% at the minimum pacing rates (101 +/- 9/min), 17% and 21% at the pacing rates of 120 and 140, respectively (p less than 0.01) in comparison with the original heart rates (96 +/- 8/min). The cardiac output also decreased significantly (p less than 0.01) during ventricular pacing. Graft flow at the original heart rates was 86 +/- 22 ml/min and the graft flow at the minimum pacing rates, at the pacing rates of 120 and 140 decreased to 73 +/- 20, 75 +/- 21, 74 +/- 23 ml/min (P less than 0.01), respectively. These reduction in the graft flow were caused by a decrease in diastolic graft flow (p less than 0.01). In the patients with a history of myocardial infarction, ventricular pacing brought about much more decrease in blood pressure, cardiac output and graft flow volume than those in patients without myocardial infarction (p less than 0.01). During atrial pacing, no significant change was observed in blood pressure and cardiac output. The graft flow was 86 +/- 21 ml/min at the original heart rates and it increased to 93 +/- 24 at the pacing rates of 120 and 95 +/- 26 ml/min at the pacing rates of 140 (p less than 0.01). These increase in graft flow during atrial pacing were attributable to an increase in diastolic graft flow (p less than 0.05). These findings suggest that the atrial pacing following aortocoronary bypass surgery brings about the beneficial effects on coronary perfusion compared with ventricular pacing.     

Acute Hemodynamic Effects of Cardiac Resynchronization Therapy in Patients with Poor Left Ventricular Function During Cardiac Surgery

Abstract   Background: Cardiac resynchronization therapy improves systolic function in patients with heart failure and left ventricular (LV) dyssynchrony. However, the effect of biventricular (BiV) pacing on perioperative hemodynamics in cardiac surgery is not well known. We investigated the acute hemodynamic response using LVdP/dt_max in patients with depressed LV function and conduction disturbances undergoing cardiac surgery. Methods: Patients with LV ejection fraction of ≤35%, QRS duration of >130 ms, and left bundle branch block undergoing aortocoronary bypass and valve surgery were included. Temporary atrial and left and right ventricular pacing wires were applied, and LVdP/dt_max was measured with a high fidelity pressure wire in the left ventricle at the end of cardiopulmonary bypass. Responders had a ≥10% increase in LVdP/dt_max. Results: Eleven patients (age 63 ± 11 years, eight males) with a LV ejection fraction 0.29 ± 0.06% were included. Compared with right ventricular pacing (782 ± 153 mmHg/sec), there was a significant improvement in the mean LVdP/dt_max during simultaneous BiV pacing (849 ± 174 mmHg/sec; p = 0.034) and sequential BiV pacing with the LV 40 ms advanced (880 ± 157 mmHg/sec; p = 0.003). Improvement during LV pacing alone was not significant (811 ± 141 mmHg/sec). Six patients were responders with simultaneous and nine with sequential BiV pacing. Only sequential BiV pacing had a significant improvement in LV systolic pressure (p = 0.02). Conclusions: BiV pacing results in acute hemodynamic improvement of LV function during cardiac surgery. Optimization of the interventricular pacing interval contributes to the effect of the therapy.     

Interaction of an implanted pacemaker with a transesophageal atrial pacemaker: report of a case

We report an interaction of a transesophageal atrial pacemaker (TAP) with a permanently implanted pacemaker in a cardiac patient who had undergone ablative therapy for atrial tachyarrhythmia 5 years earlier. The patient’s permanent A-V pacemaker was completely inhibited by the TAP, and there was loss of ventricular contractions and blood pressure. The patient required epicardial A-V pacing to overcome the programmed heart rate of 76 bpm. We describe alternative methods to epicardial pacing. We also recommend close inspection of the chest radiograph, which often can reveal the serial numbers of the implanted pacemaker, as a means of identifying the device’s functions and programming.     

Ventricular tachycardia associated with transmyocardial migration of an epicardial pacing wire

A 66-year-old man who had undergone a three-vessel coronary artery bypass grafting (CABG) procedure 3 years previously presented with ventricular tachycardia (VT) and cardiac arrest. Echocardiography demonstrated a wire coursing through the right ventricle into the pulmonary artery. The wire was removed with a snare and confirmed to be an epicardial temporary pacing wire placed during the CABG operation. We suspect that the epicardial pacing wire eroded through the right atrium and migrated into the right ventricle, contributing to the VT. Complications due to temporary epicardial pacing wires placed during CABG are discussed.     

Biventricular pacing in a patient with severe congestive heart failure

We report a case of dilated cardiomyopathy with severe congestive heart failure (ejection fraction: 19%) and complete left bundle branch block (QRS duration: 240 ms) 13 years after aortic valve replacement. Permanent biventricular pacing was implanted by inserting a left ventricular lead thorough a small left thoracotomy following intravenous insertion of right atrial and ventricular endocardial leads. Biventricular pacing increased hemodynamic parameters such as blood pressure, cardiac output and decreased mitral regurgitation. Symptoms and exercise tolerance improved dramatically. Left ventricular epicardial lead insertion via a small thoracotomy is thus useful in selected patients.     

Right paracardiac mass due to organized pericardial hematoma around retained epicardial pacing wires following aortic valve replacement

The use of temporary epicardial pacing wires during cardiac surgery is a routine procedure and has been associated with low morbidity. We describe a rare case of right paracardiac mass due to organized pericardial hematoma with right atrial compression around the epicardial pacing wires left in-situ, presenting three months following aortic valve replacement surgery. The case highlights the fact that such delayed complications can rarely occur around retained epicardial pacing wires following open heart surgery especially in patients on oral anticoagulants. The clinician should be alert to such an occurrence and during follow-up echocardiography always pay attention not only to the valve and ventricular function, but also to the pericardial and extra-pericardial space.     

Improved cardiovascular hemodynamics with atrioventricular sequential pacing compared with ventricular demand pacing

To determine the advantages of atrioventricular (AV) sequential pacing over ventricular demand pacing, paired cardiovascular hemodynamic studies were performed in each pacing mode at a constant heart rate. The paired studies included determination of ejection fraction (EF) by echocardiography and gated blood pool radionuclide scanning, and of cardiac output (CO) by the indicator-dilution method. There was no significant difference in EF with either pacing mode. Determined by echocardiography, EF with AV sequential pacing was 57% compared with 56% with ventricular demand pacing; by the gated blood pool method, EF with AV sequential pacing was 58% compared with 57% in the ventricular mode. Significant improvement with AV sequential pacing was seen in CO (4.75 L/min from 3.75 L/min; p less than 0.01); stroke volume (58 ml from 48 ml; p less than 0.02); arteriovenous oxygen content difference (4.9 vol% from 5.6 vol%; p less than 0.01); total peripheral resistance (1,724 dynes sec cm-5 from 2,025 dynes sec cm-5; p less than 0.01); and cardiac contractility, as reflected by mixing time (6.9 seconds from 8.0 seconds; p less than 0.02). No significant changes were noted in mean arterial or atrial pressure or in systemic oxygen consumption. In a second group of 6 patients, similar paired studies were done in AV sequential pacing modes before and after therapeutic reduction of total peripheral resistance. A significant increase in CO (43%) was observed following reduction in total peripheral resistance. We conclude that AV sequential pacing improves CO more effectively than ventricular demand pacing. Cardiac output can be further enhanced in patients with congestive heart failure by pretreatment with agents to reduce total peripheral resistance.     

Load dependence of cardiac output in biventricular pacing: right ventricular volume overload in pigs

BACKGROUND: Previous work from our laboratory has demonstrated that optimization of biventricular pacing is load dependent. During acute pulmonary stenosis and right ventricular pressure overload in swine, cardiac output was maximized by pacing the right ventricle 40 ms before the left ventricle. To extend those studies, this experiment examined biventricular pacing optimization during right ventricular volume overload. METHODS: After median sternotomy in 6 anesthetized domestic pigs, complete heart block was induced by ethanol ablation. A conduit was grafted from the right ventricle to the right atrium to simulate tricuspid insufficiency. During epicardial, atrial tracking DDD biventricular pacing, atrioventricular delay was varied between 60 and 180 ms in 30-ms increments. Right ventricular-left ventricular delay was varied at each atrioventricular delay from +80 ms (right ventricle first) to -80 ms (left ventricle first) in 20-ms increments. Aortic flow, right ventricular pressure, and electrocardiogram were measured at each pacemaker setting with the graft clamped and unclamped. RESULTS: Atrioventricular and right ventricular-left ventricular delays had no significant effect on cardiac output with the graft clamped. With the graft unclamped, however, there was a statistically significant (P =.003 by mixed modeling repeated measures analysis of variance) trend toward higher cardiac output with left ventricle-first pacing. CONCLUSION: Left ventricle-first biventricular pacing in swine significantly increased cardiac output during acute tricuspid insufficiency but not during the control state. Trials are warranted to develop clinical biventricular pacing for treatment of perioperative right ventricular dysfunction.     

Prevention of atrial fibrillation after cardiac valvular surgery by epicardial, biatrial synchronous pacing.

OBJECTIVE: Postoperative atrial fibrillation (AF) after cardiac surgery is a frequent complication after valvular surgery (30-60%). The purpose of this prospective, randomized study was to determine if biatrial synchronous pacing reduces postoperative AF after cardiac valvular surgery as compared to conventional therapy. METHODS: Eighty patients subjected to valvular surgery (52 men, age 66 +/- 10 years) were randomized to one of two groups: one group was treated with biatrial, synchronous pacing (BAP) for 72 h postoperatively (n=40) the other group received no atrial pacing (controls; n=40). All patients had one pair of epicardial wires attached to the right atrium. An additional electrode was placed to the left atrium in the BAP group. These patients were continuously paced at a rate of 10 beats per minute higher than the intrinsic rate starting immediately after surgery. All patients were monitored with full disclosure telemetry or Holter monitors to identify onset of AF. RESULTS: Eighteen of the 40 patients in the control group (45%) developed AF within the first 3 days postoperatively as compared to eight patients (20%) in the BAP group (P=0.02). No complications occurred associated with the placement, maintenance and removal of the atrial pacing electrodes. CONCLUSIONS: Temporary, biatrial synchronous pacing during the first 3 postoperative days is safe and has a significant rhythm-stabilizing effect in patients undergoing valvular cardiac surgery.     

Regional myocardial blood flow and coronary vascular reserve in unanesthetized ponies during pacing-induced ventricular tachycardia

To examine the effects of tachycardia on coronary circulation, transmural distribution of myocardial blood flow (MBF, 15-μm diameter radionuclide-labeled microspheres) was studied in six healthy adult ponies at rest (heart rate = 60 ± 7 beats · min^?1), during ventricular pacing at 150 and 200 beats · min^?1, as well as with ventricular pacing at 250 beats · min^?1 before and during maximal coronary vasodilatation (iv adenosine infusion; 4 μmole · kg^?1 · min^?1). Mean aortic pressure and cardiac output were unchanged from control values with ventricular pacing. Whereas ventricular pacing at 150 and 200 beats · min^?1 resulted in a progressive uniform increase in transmural MBF and well-maintained endo:epi perfusion ratio, pacing at 250 beats · min^?1 did not result in a further increase in MBF compared to pacing at 200 beats · min^?1 and the left ventricular (LV) subendocardial:subepicardial (endo:epi) perfusion ratio was significantly less than 1.00 (0.87 ± 0.05). Blood flow to the LV papillary muscles and subendocardium was significantly less than that recorded at 200 beats · min^?1. The LV endo:epi perfusion ratio with ventricular pacing at 250 beats · min^?1 during adenosine infusion resulted in a decrease in mean aortic pressure (63% of control value) and a marked further reduction in blood flow to the LV papillary muscles as well as the LV subendocardium, while MBF increased dramatically in the LV subepicardium compared to values observed during ventricular pacing at 250 beats · min^?1 alone. This resulted in a LV endo:epi perfusion ratio of 0.39 ± 0.09. By contrast, transmural right ventricular (RV) MBF increased significantly and the RV endo:epi perfusion ratio was well maintained. These data demonstrate that coronary vasomotion functions to maintain LV subendocardial blood flow in the pony myocardium at a heart rate of 200 beats · min^?1, while at 250 beats · min^?1 exhaustion of coronary vasodilator reserve in the deeper layers limits further increase in MBF.     

Biventricular pacing with coronary bypass and Dor's ventriculoplasty

We applied biventricular pacing to a patient with severe ischemic dilated cardiomyopathy (left ventricular [LV] ejection fraction 19%, LV end-diastolic volume 360 mL, and complete left bundle branch block). An epicardial LV lead was surgically implanted concomitant with on-pump beating coronary artery bypass grafting and Dor's endoventricular circular patch plasty. Biventricular pacing immediately achieved the resynchronization of the LV contraction, and improved cardiac function as well as reducing mitral regurgitation. Biventricular pacing combined with cardiac surgery for patients with cardiomyopathy and complete left bundle branch block may produce beneficial effects on LV function.     

Load dependence of cardiac output in biventricular pacing: right ventricular pressure overload in pigs

BACKGROUND: The effect of biventricular pacing on stroke volume is believed to be dependent on right ventricular/left ventricular delay, but effects in individual patients are unpredictable. This variability may reflect relative right and left ventricular volume and/or pressure overloads. Accordingly, we tested the hypothesis that the relation of cardiac output to right ventricular/left ventricular delay is load dependent in a pig model of pulmonary stenosis. METHODS: After median sternotomy in 6 anesthetized, domestic pigs, complete heart block was induced by ethanol ablation. During epicardial, atrial tracking DDD biventricular pacing, atrioventricular delay was varied between 60 and 180 ms in 30-ms increments. Right ventricular/left ventricular delay was varied at each atrioventricular delay from +80 ms (right ventricle first) to -80 ms (left ventricle first) in 20-ms increments. Aortic flow, right ventricular pressure, peripheral arterial pressure, and electrocardiogram were measured in the control state and during pulmonary stenosis, created by tightening a snare around the pulmonary artery until cardiac output decreased by 50%. RESULTS: Atrioventricular and right ventricular/left ventricular delay had no effect on cardiac output during the control state, but during pulmonary stenosis there was a statistically significant (P =.0001, repeated-measures analysis of variance) right ventricular/left ventricular delay-related trend toward higher cardiac output with right ventricular pacing first. This effect was more pronounced when the optimal atrioventricular delay was determined first, resulting in a 20% increase in cardiac output when the optimal right ventricular/left ventricular delay was compared with simultaneous biventricular pacing. CONCLUSIONS: Optimized biventricular pacing in swine is associated with increased cardiac output during acute pulmonary stenosis, but not during the control state. Further studies are needed to determine whether specific types of right ventricular and left ventricular overload predictably affect the relation between right ventricular/left ventricular delay and cardiac output.     

The effect of dopamine,atropine, phenylephrine and cardiac pacing on oxygen consumption during fentanyl-nitrous oxide anaesthesia in the dog

In animals deeply anaesthetized with fentanyl and nitrous oxide the artierial blood pressure and heart rate were increased using dopamine, atropine, electrical pacing and phenylephrine in order to study the accompanying change in whole body oxygen consumption. Seven dogs (16–24 kg) were anaesthetized with fentanyl 1 μg · kg^-1 · min^-1. After completing instrumentation a dopamine infusion was started at a rate of 39 μg · kg^-1 · min^-1. After the mean blood pressure reached 18.6 kPa the infusion was reduced to 10 μg · kg^-1 · min^-1 and maintained for 10 minutes. After waiting 45 minutes an infusion of atropine 20 μg · kg^-1 · min^-1 was started and when the heart rate reached 120 b/min the infusion was slowed to 1.25 μg · kg^-1 ’ · min^-1 and maintained for 10 minutes. Twenty-five minutes later the heart rate was increased to 150 beats/min and maintained at that level for 10 minutes using electrical pacing. The pacing was removed and an infusion of phenylephrine 5 μg·kg^-1·min^-1 was started. When the blood pressure reached 21.3 kPa the infusion was reduced to 2.5 μg · kg^-1· min^-1 and maintained for 10 minutes. The results show increases in oxygen consumption of 14 per cent with dopamine, 19 per cent with atropine, 16 per cent with pacing, and 14 per cent with phenylephrine. All changes were significantly different from the control values. The magnitude of change in whole body oxygen consumption was best predicted by either the cardiac output x blood pressure product or by the cardiac output alone.     

Salvage transvenous rapid atrial pacing to terminate atrial flutter after cardiac operations.

Atrial flutter occurring after cardiac operations normally responds well to atrial overdrive pacing through epicardial atrial pacing wires and medication. When this fails, transvenous atrial overpacing offers an attractive alternative. We performed the procedure 29 times in 25 patients. Sinus rhythm returned acutely after 25 procedures in 21 patients and persisted with medication in 20 patients at follow-up. The procedure was well tolerated by all.