Hemodynamic Benefits of Right Ventricular Outflow Tract Pacing: Comparison with Right Ventricular Apex Pacing CAREL C. DE COCK, ALBERT MEYER, OTTO KAMP, and CEES A. VISSER From the Department of Cardiology, Academic Hospital VU, Amsterdam, The Netherlands DE COCK, C.C, ET AL.: Hemodynamic Benefits of Right Ventricular Outflow Tract Pacing: Comparison with Right Ventricular Apex Pacing. To assess optimal hemodynamics in relation to stimulation site dur- ing right ventricular pacing, 17 consecutive patients who underwent cardiac catheterization were studied. In all patients, right ventricular apex and right ventricular outflow tract stimulation was performed at 85, 100, and 120 beats/min. Cardiac index at hoth pacing sites was compared using the left ventricular out- flow tract continuous wave Doppler technique. Comparison of the two stimulation sites demonstrated that right ventricular outflow tract pacing resulted in a higher cardiac index at 85 beats/min (2.42 ± 1.2 vs 2.04 ± 1.0 L/min per m^, P < 0.002) at 100 beats/min (2.78 + 1.4 vs 2.35 t 1.1 L/minperm^, P< 0.001) and 120 beats/min (3.00 ± 1.5 vs 2.61 ± 0.9L/minperm^,P< 0.001). From a total of 51 paired observations, 45 showed an increase in cardiac index during outflow tract pacing as compared to apex pacing. Right ventricular outflow tract pacing at 120 beats/min resulted in a lower cardiac index than right ventricular apex pacing in patients with significant coronary artery disease and/or impaired left ventricular function (ejection fraction ^ 50%), whereas right ventricular outflow tract pacing produced higher cardiac indices in the absence of these abnormalities. Right ventricular outflow tract pacing resulted in higher cardiac in- dices as compared to apex pacing in all other subgroups at all other pacing sites tested. It is concluded that stimulation of the right ventricular outflow tract offers a significant hemodynamic benefit during sin- gle chamber pacing as compared to conventional apex pacing, particularly in the absence of significant coronary artery disease and/or left ventricular dysfunction. (PACE 1998; 21:536-541} hemodynamics, right ventricular outflow tract pacing Introduction Upon the introduction in 1959 of a pacemaker system using a transvenous electrode,^ the right ventricular apex was advocated as the most ap- propriate pacing site, since stability of the pacing electrode represented a major problem in the ab- sence of acute fixation.^•'^ However, in recent years a variety of lead configurations have been de- signed to prevent dislocation, and alternative pac- ing sites proved to be feasible and safe with re- spect to pacing threshold, adequate sensing, and ventricular perforation."* Address for reprints: Carel C, de Cock, M.D.. Department of Cardiology, Academic Hospital VU, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands. Fax: 31-20-4442446. Received August 28, 1996; revised February 4, 1997; accepted March 10, 1997. Because of the close relation of the right ven- tricular outflow tract to the intraventricular sep- tum, right ventricular outflow tract pacing may fa- cilitate a more physiological excitation of the myocardium,''"^ resulting in a more synchronized contraction. Therefore, right ventricular outflow tract pacing may have hemodynamic benefits as compared to conventional right ventricular apex stimulation.^-^^ The object of the present study was to assess the hemodynamic effects of tempo- rary right ventricular outflow tract pacing as com- pared to right ventricular apex pacing. Patients and Methods The study included 17 consecutive patients who underwent diagnostic left and right cardiac catheterization. Their ages ranged from 31-79 years (mean 58 ± 14) (Table I). All patients had normal sinus rhythm without intraventricular 536 March 1998 PACE, Vol. 21
Transcript
Hemodynamic Benefits of Right VentricularOutflow Tract Pacing: Comparison with RightVentricular Apex Pacing
CAREL C. DE COCK, ALBERT MEYER, OTTO KAMP, and CEES A. VISSER
From the Department of Cardiology, Academic Hospital VU, Amsterdam, The Netherlands
DE COCK, C.C, ET AL.: Hemodynamic Benefits of Right Ventricular Outflow Tract Pacing: Comparisonwith Right Ventricular Apex Pacing. To assess optimal hemodynamics in relation to stimulation site dur-ing right ventricular pacing, 17 consecutive patients who underwent cardiac catheterization were studied.In all patients, right ventricular apex and right ventricular outflow tract stimulation was performed at 85,100, and 120 beats/min. Cardiac index at hoth pacing sites was compared using the left ventricular out-flow tract continuous wave Doppler technique. Comparison of the two stimulation sites demonstrated thatright ventricular outflow tract pacing resulted in a higher cardiac index at 85 beats/min (2.42 ± 1.2 vs 2.04± 1.0 L/min per m^, P < 0.002) at 100 beats/min (2.78 + 1.4 vs 2.35 t 1.1 L/minperm^, P< 0.001) and120 beats/min (3.00 ± 1.5 vs 2.61 ± 0.9L/minperm^,P< 0.001). From a total of 51 paired observations,45 showed an increase in cardiac index during outflow tract pacing as compared to apex pacing. Rightventricular outflow tract pacing at 120 beats/min resulted in a lower cardiac index than right ventricularapex pacing in patients with significant coronary artery disease and/or impaired left ventricular function(ejection fraction ^ 50%), whereas right ventricular outflow tract pacing produced higher cardiac indicesin the absence of these abnormalities. Right ventricular outflow tract pacing resulted in higher cardiac in-dices as compared to apex pacing in all other subgroups at all other pacing sites tested. It is concludedthat stimulation of the right ventricular outflow tract offers a significant hemodynamic benefit during sin-gle chamber pacing as compared to conventional apex pacing, particularly in the absence of significantcoronary artery disease and/or left ventricular dysfunction. (PACE 1998; 21:536-541}
hemodynamics, right ventricular outflow tract pacing
Introduction
Upon the introduction in 1959 of a pacemakersystem using a transvenous electrode,^ the rightventricular apex was advocated as the most ap-propriate pacing site, since stability of the pacingelectrode represented a major problem in the ab-sence of acute fixation.̂ •'̂ However, in recent yearsa variety of lead configurations have been de-signed to prevent dislocation, and alternative pac-ing sites proved to be feasible and safe with re-spect to pacing threshold, adequate sensing, andventricular perforation."*
Address for reprints: Carel C, de Cock, M.D.. Department ofCardiology, Academic Hospital VU, De Boelelaan 1117, 1081HV Amsterdam, The Netherlands. Fax: 31-20-4442446.
Received August 28, 1996; revised February 4, 1997; acceptedMarch 10, 1997.
Because of the close relation of the right ven-tricular outflow tract to the intraventricular sep-tum, right ventricular outflow tract pacing may fa-cilitate a more physiological excitation of themyocardium,''"^ resulting in a more synchronizedcontraction. Therefore, right ventricular outflowtract pacing may have hemodynamic benefits ascompared to conventional right ventricular apexstimulation.^-^^ The object of the present studywas to assess the hemodynamic effects of tempo-rary right ventricular outflow tract pacing as com-pared to right ventricular apex pacing.
Patients and Methods
The study included 17 consecutive patientswho underwent diagnostic left and right cardiaccatheterization. Their ages ranged from 31-79years (mean 58 ± 14) (Table I). All patients hadnormal sinus rhythm without intraventricular
LAD = left anterior descending coronary artery; RCA = right coronary artery; RCX = ieft circumfiex coronaryartery.' Stenosis ^90%.
conduction delays. Half bad coronary artery dis-ease, and patients with evidence of significantvalvular disease were excluded. Right beartcatheterization, including the pacing protocol,was performed prior to left ventriculograpby andcoronary angiography. The left and right femoralvenous approacb was used to position the twostimulation electrodes. A standard bipolar tempo-rary stimulation electrode (6 French, Cordis) waspositioned in tbe right ventricular apex under flu-oroscopy. Both stimulation electrodes were con-nected to an external pacemaker (Medtronic AV-PSA model 5311 [Medtronic Inc., Minneapolis,MN. USA]). The first pacing site among patientswas randomized. Patients were paced at 85, 100.and 120 beats/min. Pacing in the right ventricularoutflow tract and right ventricular apex was per-formed in an alternating fashion. Pacing at eachposition and at each heart rate was continued for2 minutes before all measurements (includingblood pressure and ecbo-Doppler measurements)were made. There was a 5-niinute minute intervalbetween the 2-minute pacing periods to allow si-
nus rhythm to return to < 10% of baseline values.Systolic blood pressure, diastolic blood pressure,and mean arterial pressure were measured usingan automatic monitor [Critikon Dynamap vitalsigns monitor, model 1846 [Critikon Inc., Tampa,FL, USA]). A Hewlett-Packard Sonos 1000 (model77020 [Hewlett-Packard, Andover, MA, USA])witb a 3.5-MHz continuous wave transducer wasused for all echocardiographic and cardiacDoppler studies. The highest audio signal andsharpest outline were used to assess optimal reg-istration of blood flow velocities in the ascendingpart of the aortic arch. Measurements of Dopplerrecordings were performed offline using a com-puter-assisted digitalization system. Continuouswave recordings were measured using the maxi-mal envelope. The area under the Doppler flowvelocity curve was determined by digitizing thesignal from baseline to baseline.^' An average ofsix consecutive cycles was used to calculate car-diac output. Cardiac output was calculated as thesystolic velocity integral X aortic root area Xheart rate. The aortic root area was measured by
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DE COCK, ET AL.
M-mode echocardiography using the parasternallong axis view. Heart rate was measured usiugiwo consecutive spikes on the ECG. All measure-ments were performed by two experiencedechocardiographers. who were blinded for thepacing mode. Differences in functional parame-ters for different pacing sites were assessed usingthe f-test. ANOVA was used to determine differ-ences between subgroups of patients. All data areexpressed as mean ± SD. P < 0.05 was consideredstatistically significant.
Results
The mean cardiac index with sinus rhythmand intact AV conduction was 2.2 ± 1.0. Sinusrate accelerated < 10% as measured at the end ofeach 2-minute pacing period. There was no signif-icant difference in increase of sinus rate and site ofpacing.
Mean cardiac index was higher during rightventricular outflow tract pacing as compared toconventional right ventricular apex pacing atall stimulation rates [Table II). Increase in cardiacindex was 19% at 85 beats/min, 18% at 100 beats/min, and 15% at 120 beats/min. From a total of51 paired observations, 45 showed an increase incardiac index during right ventricular outflowtract pacing. A decrease in cardiac index of^ 5 % during right ventricular outflow tract pacingwas observed in 1 patient at 85 beats/min, 3patients at 100 beats/min, and 2 patients at 120beats/min. No patient showed a decrease incardiac index of >: 5% during all three pacing
Table II.
Hemodynamic Parameters Measured at the Two PacingSites During Pacing at 85, 100, and 120 Beats-Min
MAPCl
MAPCl
MAPCl
RVOT
8597 ± 13
2.42 ± 1.2100
102 ± 102.78 ± 1.4
12099 ± 13
3.00 ± 1.5
RVAP
beats/mm99 ± 12
2.04 ± 1.0beats/min
100 ± 112.35 ± 1.1
beats/min99 ± 12
2.61 ± 0.9
P Value
< 0.002
<0.01
< 0.01
Cl = cardiac index; MAP = mean arterial pressure; RVAP =right ventricular apex; RVOT = right ventricular cutflow tract.
rates. Results were not dependent on first (ran-domly chosen) pacing site.
Although mean cardiac index was signifi-cantly higher during right ventricular outflowtract pacing, in individual subjects the changein cardiac index ranged from a 29% decreaseto 91% increase. Figure 1 shows the individualchange in cardiac index in relation to stimulationsite at 85, 100, and 120 beats/min. A numberof variables were evaluated to assess possiblemechanisms responsible for tbese differences.These variables included resting cardiac index,the presence of a previous myocardial infarction,severe [^ 90%) occlusion of the left anteriordescending artery, left circumflex artery, and
Cardiac index
SSbpn
RVAP RVOT
p < 0.002
100 hpm
RVAP
Figure 1. Mean cardiac index during right ventricular apex pacing (RVAP) and right ventricularoutflow tract pacing (RVOT) at 85, 100, and 120 beats/win.
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right coronary artery, and an ejection fraction< 0.50.
From the group of eight patients with im-paired left ventricular function (ejection fraction^ 0.50) or significant coronary artery disease, fiveshowed a decrease in cardiac index during rightventricular outflow tract pacing at 120 beats/min.In the group of nine patients without impaired leftventricular function or coronary artery disease,one showed a decrease (P < 0.05). At all other pac-ing rates no subgroup demonstrated significantbenefits during right ventricular apex pacing(Tahle III).
No differences were present in current con-sumption (mA) at 0.5 ms during apex pacing (1.28± 0.48) versus outflow tract pacing (1.24 ± 0.44, P^ NS). In addition, R wave sensing (mV) duringapex pacing and outflow tract pacing were com-parahle (10.1 ± 2.3 vs 9.9 ± 2.0, P = NS).
Discussion
Selection of the right ventricular apex as thepreferred site of permanent endocardial pacingwas hased mainly on the stability of the pacingelectrode in this position, although the initial dis-location rate was high. With the introduction ofactive fixation^^ and alternative electrode designs,alternative pacing sites proved to be safe and fea-sible with respect to pacing thresholds, adequatesensing, and stability, although studies are lim-ited.'' Although the influence of pacing site on leftventricular contraction has been studied in a num-ber of animal studies,^^" '̂̂ limited data exist on thehemodynamic response of different endocardiacpacing sites in humans. In the present study there
Table III.
Increase or Decrease in Cardiac Index During RightVentricular Outflow Tract Pacing (at 120 beats/min)Related to the Presence of CAD and/or EF ^ 0,50
was a significant increase in cardiac index duringright ventricular outflow tract pacing as comparedto conventional right ventricular apex pacing,which was probably related to altered ventriculardepolarization from the latter pacing site resultingin reduced myocardial function. Previous studiesdemonstrated that different ventricular pacingsites have a major influence on left ventricularperformance. Wiggers'^ suggested that the amountof ventricular mass not effectively involved inventricular contraction is dependent directly onthe distance between the pacing site and the pointof entry of the activation front into the Purkinjesystem. This concept was supported by the elec-trophysiological studies of Lister et al.^'' and sub-sequently was observed by others.^^'^^ Kosowskyet al.^^ compared synchronous His-bundle pacingthereby maintaining the normal pattern of activa-tion with synchronous right ventricular outflowtract pacing in dogs. Ventricular function mea-sured by peak left ventricular dp/dt and left ven-tricular pressure was increased significantly in thepresence of normal ventricular activation.
Tbe sparse data reported with respect tohemodynamic effects and different pacing site inman^"'̂ ^ have presented varying results, probablyrelated to methodological limitations. Benchimoland Liggett^^ found no differences in cardiac out-put in six patients when artificial endocardialstimulation was performed at a fixed rate of 100beats/min in the outflow tract, or mid-portion orapex of the right ventricle. However, their conclu-sion was based on a small number of subjects andonly one pacing rate was studied. Barold et al.^''studied a group of 52 patients and compared en-docardial pacing at different rates from outflowand inflow tracts of the right ventricle. No influ-ence on site of ventricular pacing on cardiac per-formance could be demonstrated using thermodi-lution for hemodynamic measurements. Patientselection represented a major limitation in thisstudy since a high number of patients (37%) hadchronic obstructive lung disease, which has a sig-nificant influence in variability of thermodilutionmeasurements.^"
Raichlen et al.^^ compared right ventricularoutflow tract pacing with right ventricular apexpacing at 100 heats/min in eight patients under-going cardiopulmonary bypass surgery andreported no significant differences in cardiac
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DE COCK. ET AL.
output. However, epicardial pacing in anes-thetized patients with an open pericardium mayaffect left ventricular performance and cannot hecompared to that in suhjects with intact peri-cardium in the unanesthetized state.
Several factors may he responsible for the im-proved cardiac performance during right ventric-ular apex pacing, which may reflect alteration ofthe electrical activation sequence of the ventricles.Pacing from the right ventricular apex may affectthe competence of mitral valve closure andtherehy alter left ventricular end-diastolic vol-ume. Yellin et al.^^ concluded from animal studiesthat balanced diastolic chordal tension creates op-timal conditions for mitral valve closure at end di-astole. Grover and Elantz^° found altered transientinward wall motion at end diastole from differentpacing sites that caused an increase in mitral re-gurgitation or impaired diastolic filling resultingin altered end-diastolic volumes. Thus, increasedamounts of mitral regurgitation may be associatedwith right ventricular apex pacing resulting in anincrease in end-diastolic volume and cardiac per-formance. In addition, alterations in ventricularinteraction may affect end-diastolic volume. Littleet al.^^ demonstrated that transseptal pressure gra-dient and the resulting asynchrony between rightand left ventricular performance is dependent onmotion of the interventricular septum. In thepresent study, 12-lead ECG invariably demon-strated absence of septal q waves during right ven-
tricular apex pacing in leads V̂ and Vg while qwaves were present during outflow tract pacing,which might reflect a more physiological inter-ventricular depolarization.
Patients with advanced coronary artery dis-ease and/or impaired left ventricular functionshowed a decrease in cardiac index during pacingat 120 beats/min from the right ventricular out-flow tract as compared to the right ventricularapex. Since this was only ohserved at the highestrate, regional ischemia may be responsible for thisphenomenon. In the presence of significant coro-nary artery disease, pacing may precipitate re-gional ischemia and local contraction abnormali-ties. Initiating activation from these regions mayresult in a less effective contraction sequence.^^
The recent introduction of rate responsivepacing in patients proved to be hemodynamicallybeneficial as compared to VVI pacing, resulting inincreased cardiac performance.^* The observed in-crease in exercise performance of about 15%-20%is comparable to the increase in cardiac outputfound in the present study during right ventricu-lar outflow tract pacing. Provided improved car-diac performance from the right ventricular out-flow tract is maintained during permanent pacing,a significant improvement can be accomplishedwith substantial cost reductions in virtually allimplantations with single chamber stimulation.Whether or not similar findings are present duringdual chamber pacing remains to be established.
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