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.     

Institution of Physiological Pacing Utilizing Preexisting Hardware

Six patients with ventricular inhibited pacemakers, who experienced adverse effects from loss of atrial contribution to cardiac output and loss of atrioventricular synchrony, were successfully converted to atrial demand (3 patients) and atrioventricular sequential systems (3 patients). The preexisting ventricular pulse generator was used for atrial pacing in 3 patients, and the preexisting ventricular leads were employed for atrioventricular sequential pacing in 3 patients. The advantages and potential risks of utilizing preexisting hardware for conversion of ventricular pacing into physiological pacing are discussed.     

An inordinate elevation in pacing threshold after myocardial electrode implantation

An inordinate elevation in pacing threshold beyond a maximal output of the pulse generator was observed in 4 patients during the acute interval following permanent pacemaker implantation using a myocardial electrode. Pacemaker implantation was performed in these patients (9 months, 11 months, 5 years and 32 years of age) for the treatment of brady-arrhythmias (complete A-V block or atrial fibrillation) developed following open heart surgery. In two infants, hypopotassemia caused transient pacing failure due to an increase in threshold over 5 volt. In other two patients, threshold increased to levels more than 10 volt within 36 and 12 days probably due to unsuitable pacing site, and then the pulse generators were removed. It is important to measure threshold periodically after permanent pacemaker implantation and to consider the possibility of an inordinate elevation in threshold.     

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.     

Temporary A-V sequential pacing using transluminal pacing electrodes

A case is presented which describes the initiation of atrialventricular (A-V) sequential pacing using atrial epicardial wires and an in situ transluminal ventricular pacing probe. A 68year-old female with a permanent A-V sequential pacemaker was scheduled for elective aortocoronary bypass. Following sternotomy, pacing function was converted to ventricular pacing (WI) with the use of electrocautery. A Chandler® V-pacing probe was introduced through a Paceport® (American Edwards) pulmonary artery catheter and with a paced increase in ventricular rate, the cardiac output increased from 2.8 to 3.2 L · min^-1. At the conclusion of cardiopulmonary bypass the patient was in sinus rhythm at a rate of 67 · min^-1 and was paced to a faster rate using bipolar atrial epicardial wires. The patient subsequently developed intermittent heart block so temporary A-V sequential pacing was established using atrial epicardial wires and the in situ ventricular pacing probe. Pacing was achieved at routine generator output settings of seven milliamps (mA) for both atrium and ventricle and at an A-V interval of 0.120 sec. This resulted in an immediate increase in cardiac output from 3.3 to 4.1L- min^-1. The compatability of these two pacing systems offers an increased margin of safety in cardiac surgery patients requiring atrial pacing, who are at risk for developing postoperative heart block.     

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.     

Atrial pacing thresholds measured in anesthetized patients with the use of an esophageal stethoscope modified for pacing

Transesophageal atrial pacing (TAP) with the use of standard, thermistor-equipped, esophageal stethoscopes, modified for pacing by incorporation of a 4-French, bipolar TAP probe (pacing esophageal stethoscope [PES]), was evaluated in 100 adult patients under general anesthesia. A commercially available TAP pulse generator supplied 10-ms pulses with current variable between 0 and 40 mA. Pacing distances (in centimeters) were measured from the infraalveolar ridge to midway between PES electrodes (1.5-cm interelectrode distance). Pacing thresholds (milliamperes) were measured at the point of a maximum-amplitude P-wave (PMAX) in the bipolar esophageal electrogram and points 1 cm proximal or 1, 2, or 3 cm distal to PMAX. TAP (70-100 beats per min) was used for sinus bradycardia less than or equal to 60 beats per min (36 patients) or atrioventricular (AV) junctional rhythm (2 patients) and blood pressure changes with TAP documented. In male patients (n = 49), PMAX was 32.7 +/- 0.3 cm (mean +/- SE) and minimum pacing threshold 5.1 +/- 0.4 mA (range, 1-13 mA) at 33.6 +/- 0.3 cm (range, 30-37 cm). In female patients (n = 51), PMAX was 30.4 +/- 0.4 cm and minimum pacing threshold 4.4 +/- 0.4 mA (range, 2-14 mA) at 31.1 +/- 0.4 cm (range, 26-40 cm). TAP produced an average 13-16 mmHg increase in systolic, diastolic, or mean arterial pressure in patients with sinus bradycardia or AV junctional rhythm. There were no subjective patient complaints (epigastric discomfort, dysphagia) that could be attributed to TAP; objective evaluation (esophagoscopy) was not performed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Atrioventricular Sequential Pacemakers: Indications,Complications, and Long-Term Follow-up

Our experience with 32 patients with atrioventricular (AV) sequential pacemakers and an average follow-up of 22 months is presented. The pertinent literature and physiology are reviewed. The indications, advantages, and complications of AV sequential pacemakers are analyzed. Half of the patients required bifocal pacing for control of arrhythmia alone, while half required control of arrhythmia associated with congestive heart failure due primarily to a noncompliant left ventricle. It is anticipated that the hemodynamic improvement occurring as a result of AV sequential pacing will increase the use of this mode of cardiac pacing in selected patients.     

Influence of atrioventricular synchrony on hemodynamics in patients with normal and low ejection fractions following open heart surgery

The authors wished to test the hypothesis that atrioventricular synchrony has a relatively greater effect on hemodynamic parameters in postoperative patients with low ejection fractions compared to those with normal ejection fractions. Temporary pacing wires were placed on the right atrium and right ventricle of patients undergoing open heart surgery. Duplicate thermodilution cardiac outputs were determined during atrial pacing and ventricular pacing at 100 beats/min. Mean left atrial and systemic blood pressures were monitored. Thirteen patients with ejection fractions of 45 per cent or less (range 24 to 45%, mean 37.3%) were included in the low ejection fraction group, and 27 patients with ejection fractions of 59 per cent or greater (range 59 to 80%, mean 66.8%) were considered in the normal ejection fraction group. All hemodynamic parameters improved significantly when changing from ventricular pacing to atrial pacing in both the normal ejection fraction group and low ejection fraction group (P less than 0.05). The magnitude of change between the groups showed no significant difference for all parameters except left atrial pressure, which decreased by a greater percentage in the low ejection fraction group with atrial pacing (P less than 0.001). The atrial contribution to hemodynamic enhancement is important in patients with normal and low ejection fraction following open heart surgery. Patients with low ejection fractions do not sustain a relatively greater reduction in cardiac output, stroke volume index, or systemic blood pressure with loss of atrioventricular synchrony when compared to patients with normal ejection fractions.     

Pacing at a Very Short Pulse Width

From March, 1973, to June, 1975, 112 variable pulse width pulse generators (Medtronic 5931, 5961) were implanted in 109 patients. The devices were used routinely with both acute (59) and chronic (53) pacing electrodes. No special technique to obtain an unusually low pacing threshold was used or necessary.A chronic pulse width of 0.29 ± 0.07 msec was set, and no patient had failure to pace in the absence of severe electrode malfunction. Follow-up of between two and four and a half years is available on 93% (104) of the series, 8 patients having been lost to follow-up. A total of 38 pulse generators are out of service because of death unrelated to pacing (11), death related to pacing (3), electrode malfunction (16), pulse generator failure (5), or miscellaneous causes (3). Actuarial analysis for pulse generator failure shows a 92% survival at three years and 85% at four years with a total of 66 pulse generators remaining in service. Similar analysis shows a consistent incidence of 6% per year for both electrode malfunction from all causes and patient death from all causes.Clinical pacing at a pulse width shorter than that commonly used is safe and practical and results in a significant increase in the longevity of mercury cell-powered pacemakers. With the high cost and limited real-time longevity experience with pacemakers powered by lithium cells, a standard mercury-zinc pulse generator remains an acceptable alternative in selected patients.     

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.     

Acute hemodynamic benefit of multisite ventricular pacing after congenital heart surgery

BACKGROUND: Cardiac dysfunction after congenital heart surgery is a major cause of morbidity and mortality. Cardiac resynchronization through multisite ventricular pacing (MSVP) improves cardiac index and ventricular function, and lowers systemic vascular resistance (SVR) in adults with heart failure and interventricular conduction delay. METHODS: The acute hemodynamic effects of MSVP after congenital heart surgery were assessed. Twenty-nine patients (aged 1 week to 17 years) with prolonged QRS interval had atrial and ventricular unipolar epicardial temporary pacing leads placed at surgery. Group 1 consisted of patients with a single ventricle (n = 14); group 2 included patients with two-ventricle anatomy (tetralogy of Fallot, ventricular septal defect) undergoing ventricular surgery (n = 10); and group 3 included patients with two-ventricle anatomy undergoing other cardiac surgery (n = 5). At a mean postoperative day 1 (range, 0 to 6), blood pressure, systemic and mixed venous oxygen saturations, electrocardiograms, and echocardiograms were obtained before and after 20 minutes of MSVP. RESULTS: The QRS duration decreased with MSVP in all patients (mean, 23%, p < 0.005). Systolic blood pressure improved in all patients (mean, 9.7%, p < 0.005). Cardiac index improved in 19 of 21 patients tested, with no change in 2 patients (mean, 15.1%, p = 0.0001). In 2 patients, MSVP facilitated weaning from cardiopulmonary bypass. Echocardiographic mitral or tricuspid valve inflow was not significantly different with MSVP. CONCLUSIONS: Multisite ventricular pacing results in improved cardiac index and increased systolic blood pressure, and it can also facilitate weaning from cardiopulmonary bypass. Multisite ventricular pacing may be used as adjunct to standard postoperative treatment of cardiac dysfunction after congenital heart surgery.     

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.     

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.     

Ineffectiveness and potential proarrhythmia of atrial pacing for atrial fibrillation prevention after coronary artery bypass grafting

BACKGROUND: Atrial pacing is often used empirically to suppress atrial ectopy and prevent atrial fibrillation after coronary artery bypass grafting. METHODS: To determine whether atrial overdrive pacing reduces atrial fibrillation and atrial ectopy after coronary artery bypass grafting, 100 patients were randomized to no atrial pacing (Control) versus AAI pacing at 10 beats/min or more above the resting heart rate (Paced), started by postoperative day 1 and continued through day 4. Major end points were new atrial fibrillation and frequency of atrial ectopy during the first 4 days after coronary artery bypass grafting. RESULTS: Atrial fibrillation occurred by day 4 in 13 of 51 (25.5%) Paced and in 14 of 49 (28.6%) Control patients, p = 0.90. Control patients who developed atrial fibrillation had significantly more atrial ectopy than those who did not. Atrial ectopy was paradoxically more frequent in the Paced group (2,106+/-428 versus 866+/-385 per 24 hours, p = 0.0001). Loss of capture, sensing, and consistent atrial pacing occurred frequently during atrial pacing. CONCLUSIONS: Contrary to prevailing opinion and practice, postoperative atrial overdrive pacing significantly increases atrial ectopy and does not reduce the likelihood of atrial fibrillation.     

Effects of magnesium sulphate on atrioventricular conduction times and surface electrocardiogram in dogs anaesthetized with sevoflurane

We have studied the effects of magnesium on atrioventricular (AV) conduction times and surface electrocardiogram during both sinus rhythm and atrial pacing in seven dogs anaesthetized with 1 MAC of sevoflurane. A bolus dose of magnesium sulphate (MgSO4) 30, 60 and 90 mg kg-1 significantly increased plasma magnesium concentrations from 1.3 (SEM 0.1) to 15.3 (1.3) mg dl-1. MgSO4 significantly prolonged A-H (AV nodal conduction time during sinus rhythm), St-H (intra-atrial and AV nodal conduction time during atrial pacing) and H-S (total ventricular conduction time) intervals at doses > or = 30 mg kg-1 ; H-V interval (His-Purkinje conduction time) at doses > or = 60 mg kg-1; RR and PR intervals and QRS duration at doses > or = 30 mg kg-1 in a dose- related manner during both sinus rhythm and atrial pacing. QTc interval remained unchanged during sinus rhythm. The doses of MgSO4 used did not have deleterious effects on AV conduction times and surface electrocardiogram during 1 MAC of sevoflurane anaesthesia. This finding suggests that MgSO4 in high doses was safe and may be indicated for cardiac arrhythmia and hypertension during sevoflurane anaesthesia. However, further study is required to apply these findings to clinical anaesthesia.      

Complex arrhythmia analysis in uraemic haemodialysed patients

Impulse formation and conduction disturbances of the heart were investigated in 23 uraemic patients with transvenous and oesophageal electrodes. Utilizing regular atrial pacing the sinoatrial conduction time (SACT) was obtained and sinus automaticity was evaluated by measurement of the sinus node recovery time (SNRT). The atrial effective refractory period and the Wenckebach point were also determined. The effects of regular haemodialysis treatment on impulse formation and propagation disorders caused by uraemia were observed. In 16 patients transitory or permanent cardiac stimulation had to be carried out because of 2nd and 3rd degree AV block.No complication was observed during simultaneous haemodialysis and pacemaker treatment.It is concluded that the non-invasive, simple bedside oesophageal atrial stimulation method is a good alternative and should be used in the exact diagnosis of heart conduction disturbances of haemodialysed patients.     

Atrioventricular conduction during adenosine-induced hypotension in dogs anaesthetized with sevoflurane

We have studied the effects of adenosine-induced hypotension on A-H interval (atrioventricular (AV) nodal conduction time during sinus rhythm), St-H interval (intra-atrial plus AV nodal conduction time during atrial pacing), H-V interval (His-Purkinje conduction time) and H-S interval (total ventricular conduction time) by His-bundle electrocardiography in addition to surface electrocardiogram during both sinus rhythm and atrial pacing in nine dogs anaesthetized with 1 MAC of sevoflurane. Stepwise increases in infusion rates of adenosine to 0.1, 0.3, 0.5 and 1.0 mg kg-1 min-1 produced a dose-related decrease in mean arterial pressure from 91 (6) to 38 (2) mm Hg. Adenosine significantly increased the A-H interval at infusion rates of 0.5 mg kg- 1 min-1 and above, and the St-H interval at 1.0 mg kg-1 min-1. The H-V and H-S intervals remained unchanged. Heart rate decreased significantly only at 1.0 mg kg-1 min-1 with a significant increase in the PR interval. Adenosine-induced hypotension did not have deleterious effects on AV conduction times and the surface electrocardiogram in dogs anaesthetized with 1 MAC of sevoflurane. This may indicate that the effects of adenosine on AV conduction were small and therefore are unlikely to be a contraindication to the use of adenosine for inducing hypotension in patients with initially normal conduction during sevoflurane anaesthesia.      

Comparison of longevity, pacing, and sensing characteristics of steroid-eluting epicardial versus conventional endocardial pacing leads in children

OBJECTIVE: Because of either cardiac anatomy or small size, pacing in children often occurs by means of epicardial leads. The disadvantage of epicardial leads is the shorter longevity of these leads compared with endocardial leads. During short-term follow-up, improved stimulation thresholds were found for the newer steroid-eluting epicardial leads. The longevity of these leads may be better than that of conventional epicardial leads. An improved longevity of epicardial leads may influence the choice to either epicardial or endocardial pacing in children. METHODS: We studied the longevity and the pacing and sensing characteristics of 33 steroid-eluting epicardial pacing leads (group I, 15 atrial, 18 ventricular) implanted between November 1991 and October 1996 in 20 children with a mean age of 7.6 +/- 6.5 years (mean +/- SD), and 29 endocardial pacing leads (group II, 15 atrial, 14 ventricular) implanted during the same period in 21 children with a mean age of 11.7 +/- 4.7 years. RESULTS: The mean follow-up in group I was 2.9 +/- 1.6 years and in group II 3.1 +/- 1.7 years (P =.61). The 2-year survival of the leads in group I was 91% +/- 5% and in group II 86% +/- 7% (P =.97). Lead failure occurred in both groups in 4 leads (P =.85). Chronic stimulation and sensing thresholds were similar. CONCLUSIONS: Steroid-eluting epicardial leads have the same longevity as the conventional endocardial leads. Pacing and sensing thresholds were similar and did not change during follow-up. Therefore steroid-eluting epicardial pacing leads are a good alternative for endocardial leads in small children and in children with congenital heart disease.     

Hemodynamic effects of various modes of cardiac pacing after operation for idiopathic hypertrophic subaortic stenosis

The hemodynamic effects of varying heart rate and pacing site were studied in 6 patients with idiopathic hypertrophic subaortic stenosis following operative relief of outflow obstruction. Ventricular pacing (117 beats per minute) resulted in a 26% decrease in cardiac output (p less than 0.02), a 54% increase in pulmonary capillary wedge pressure (p less than 0.03), and a 23% decrease in mean blood pressure (p less than 0.05), compared with normal sinus rhythm (88 beats per minute). Slow atrial pacing (112 beats per minute) did not significantly alter any hemodynamic variable compared with normal sinus rhythm. Rapid atrial pacing (143 beats per minute) produced a similar degree of hemodynamic impairment as ventricular pacing. This study demonstrates that ventricular pacing at heart rates commonly used clinically and rapid atrial rates result in a significant fall in cardiac output. Preservation of atrial systole at heart rates that allow adequate diastolic ventricular filling of a hypertrophied, noncompliant ventricle is stressed. In addition, atrial electrodes are useful to record atrial electrograms or induce rapid atrial stimulation to treat supraventricular tachyarrhythmias.