Left Ventricular Septal and Left Ventricular Apical Pacing Chronically Maintain Cardiac Contractile Coordination, Pump Function and EfficiencyCLINICAL PERSPECTIVE
Background— Conventional right ventricular (RV) apex pacing can lead to adverse clinical outcome associated with asynchronous activation and reduced left ventricular (LV) pump function. We investigated to what extent alternate RV (septum) and LV (septum, apex) pacing sites improve LV electric activation, mechanics, hemodynamic performance, and efficiency over 4 months of pacing.
Methods and Results— After AV nodal ablation, mongrel dogs were randomized to receive 16 weeks of VDD pacing at the RV apex, RV septum, LV apex, or LV septum (transventricular septal approach). Electric activation maps (combined epicardial contact and endocardial noncontact) showed that RV apical and RV septal pacing induced significantly greater electric desynchronization than LV apical and LV septal pacing. RV apex and RV septal pacing also significantly increased mechanical dyssynchrony, discoordination (MRI tagging) and blood flow redistribution (microspheres) and reduced LV contractility, relaxation, and myocardial efficiency (stroke work/myocardial oxygen consumption). In contrast, LV apical and LV septal pacing did not significantly alter these parameters as compared with the values during intrinsic conduction. At 16 weeks, acute intrasubject comparison showed that single-site LV apical and LV septal pacing generally resulted in similar or better contractility, relaxation, and efficiency as compared with acute biventricular pacing.
Conclusions— Acute and chronic LV apical and LV septal pacing maintain regional cardiac mechanics, contractility, relaxation, and efficiency near native levels, whereas RV apical or RV septal pacing diminish these variables. Acute LV apical and LV septal pacing tend to maintain or improve contractility and efficiency compared with biventricular pacing.
Received May 28, 2009; accepted August 24, 2009.
Compared with normal ventricular activation, conventional right ventricular (RV) apex pacing is associated with asynchronous left ventricular (LV) activation, abnormal contraction, and reduced pump function (for review, see reference 1).1 These adverse effects have been associated with an increased risk of developing heart failure (for review, see reference 1).1 Also contributing to this adverse outcome is a reduction in myocardial efficiency during ventricular pacing, which increases total myocardial oxygen demand. Consequently, paced hearts can be expected to be more susceptible to ischemia when coronary reserve is limited,2 as during coronary artery disease and/or overload of the heart.
Clinical Perspective on p 571
Several studies have sought alternative pacing sites to improve hemodynamic performance. Because pacing leads are usually implanted transvenously, alternate sites within the RV have been studied most intensively, but results of the various studies are mixed.3,4 Experimental and clinical studies indicate that LV pacing sites often render better hemodynamic performance than RV pacing sites.5–7 In a previous acute canine study, we observed hemodynamic benefits by LV septal and LV apical pacing, compared with RV apical pacing, and mixed effects during RV septal pacing.8 No studies have directly addressed the influence of alternate site pacing on myocardial efficiency. One patient study found that cardiac resynchronization improves efficiency as compared with left bundle-branch block,9 whereas other studies showed that RV pacing decreased efficiency as compared with atrial pacing.10,11
It was the aim of this study to compare the long-term (4 months) effects of pacing at the RV apex, RV septum, LV septum, and LV apex in canine hearts by measuring the sequence of electric activation as well as the distribution of myocardial strains, blood flow, pump function, and myocardial efficiency. In addition, it was investigated how single-site LV pacing compares with biventricular (BiV) pacing.
Animal handling was performed according to the Dutch Law on Animal Experimentation (WOD) and the European Directive for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes (86/609/EU). The protocol was approved by the Maastricht University Experimental Animal Committee.
Acute Electric Activation Mapping
To avoid the physical influence of the electrode bands and Ensite balloon on the other measurements, electric activation mapping was performed in 7 separate animals, using the same anesthesia (below). Epicardial activation was determined using 2 bands of unipolar electrodes (104 in total) around the LV and RV, whereas endocardial activation was determined using Ensite noncontact mapping. Electrograms from the 64 physical electrodes on the Ensite balloon were converted by the Ensite system into 2048 virtual electrograms from the endocardial surface of the LV. These virtual electrograms were exported to a personal computer, where activation time was determined from the time of steepest negative deflection of the electrogram using custom software. All electrograms were time-referenced to the onset of the Q-wave (natural conduction) or the pacing artifact.
Chronic Ventricular Pacing Model
Adult mongrel dogs (28±3.5 kg) of either sex were premedicated, anesthetized, and treated after surgery as described before.12 All received a transvenous lead in the right atrium (Medtronic 5568) and were randomized to receive either an epicardial lead at the LV apex (n=7; Medtronic 5071) via a limited thoracotomy or a transvenous lead in either the RV apex (n=9; Medtronic 3830 or 5076), RV midseptum (n=7; Medtronic 3830), or the LV midseptum (n=8). The latter received a custom pacing lead (Medtronic 3830 lead) with extended helix that was introduced transvenously and, after positioning against the RV septum using a preshaped guiding catheter, driven through the interventricular septum with the screw-in tip until the LV endocardium was reached. All leads were positioned according to the prescribed anatomic location; no attempt was made to search for sites resulting in narrower paced QRS complexes. After creation of total AV block by radiofrequency ablation, the animal was paced for 16 weeks in VDD mode (Medtronic Sigma, Kappa, or Enpulse series). AV delay (110±20 ms) was set to maintain P-Q segment length on ECG lead II as measured just before creation of AV block. Under all conditions, pacing was performed at about twice the stimulation threshold.
MRI Tagging Measurements of Strain, Dyssynchrony, and Discoordination
After 16 weeks of VDD pacing but before the final invasive measurements (below), MRI tagging was performed in 5 short-axis slices, spanning most of the LV wall, at a temporal resolution of 15 ms.12 Myocardial strains, work, and indices of global mechanical discoordination (internal stretch fraction [ISF])13 and dyssynchrony (difference between 5th and 95th percentiles of time to peak shortening measured from 160 locations) were determined as explained in more detail in the online-only Data Supplement.
Temporal Changes in Hemodynamics and Efficiency
Measurements were recorded at 3 time points, all under full anesthesia: (1) after lead implantation but before AV block and paced in AOO mode at 110 bpm (baseline), (2) after AV block creation and approximately 1 hour of DOO pacing at the same rate (1 hour of ventricular pacing [V-pacing]), and (3) again under the same surgical and pacing conditions after 16 weeks of VDD pacing (16 weeks of V-pacing). Typical sinus rate under anesthesia was 70 to 90 bpm, and slight overdrive AOO/DOO pacing was used to reduce hemodynamic variability and rate effects during and between measurements. During DOO pacing, AV delay was increased relative to VDD to maintain P-Q segment length.
LV pressure and volume were determined using the conductance catheter technique (CD-Leycom, The Netherlands).14 All signals (ECG, pressure, volume) were digitized at 1 kHz and stored using custom-made software (IDEEQ, Maastricht Instruments, The Netherlands) and later analyzed using custom automated analysis software written for MATLAB (MathWorks, Natick, Mass).
LV contractility was assessed as the peak rate of pressure rise normalized to instantaneous chamber pressure (LVdP/dtmax/Pinstantaneous). LV relaxation was assessed as the time constant of the exponential decay fit to the falloff of LV pressure from maximal rate of decline until the level of end-diastole (τ). Mechanical interventricular asynchrony was quantified as the time delay between the upslope of the LV and RV pressure signals, estimated by cross-correlation.15 Stroke work (SW) was calculated as the loop area enclosed in the LV pressure-volume (P-V) plane. External efficiency was calculated as the ratio of SW to myocardial oxygen consumption (MVO2, see below).16
Myocardial Oxygen Consumption and Perfusion
MVO2 (mL O2/beat) was calculated according to the Fick principle (product of mean myocardial blood flow, arterial to coronary venous oxygen content difference, and inverse heart rate). Mean myocardial blood flow was indexed by continuous measurement of coronary sinus blood velocity, measured by Doppler wire (Volcano Therapeutics 1400). Average coronary sinus blood velocity was calibrated to mean myocardial blood flow17 by simultaneous Doppler velocity and microsphere flow measurements,18 once for each of the 3 hemodynamic measurement time points above. After the calibration measurement, any changes in average coronary sinus velocity were assumed to be linearly proportional to a change in mean myocardial flow.17
Fluorescent microsphere measurements were also used to determine regional myocardial perfusion as previously described.18 Postmortem samples of the anterior, lateral, posterior, and septal wall were assessed to determine distribution of myocardial blood flow within the LV wall.
Acute Comparative Pacing at 16 Weeks
After finishing the temporal measurements at 16 weeks, the thorax was opened and epicardial leads were placed at the RV apex, LV apex (in nonchronically LV-apical paced animals), and LV lateral wall. The same measurements described above were repeated during DOO pacing at 110 bpm in 4 modes: implant site (IS) pacing, RV apical pacing, LV apical pacing, and RV apical/LV lateral pacing (BiV). In this way, each chronic implant site could be compared with 3 reference sites/combinations within each animal (see Data Supplement).
Data are presented as mean±SD. Unless otherwise indicated, temporal data during V-pacing are expressed as the percent difference from the global mean baseline (AOO) value. Data on acute comparative pacing after 4 months of ventricular pacing are expressed as the percent difference from pacing at the implant site in that particular group at 16 weeks. The effects of pacing over time within subjects compared with baseline and differences between the RV apex paced group to the other groups (as well as all 4 groups to the normal conduction group for MRI tagging parameters), and separately, the effects of acute comparative pacing were evaluated for statistical significance using repeated-measures ANOVA (standard ANOVA for MRI tagging parameters) and the Sidak correction for multiple comparisons using a family significance level of α=0.05.
Details of lead position verification are included in the Data Supplement.
Acute Electric Activation Mapping
The left panel of Figure 1 depicts the electric activation sequence during normal conduction. The red to yellow colors indicate that total ventricular activation occurred within 40 ms. During RV apical pacing, the RV wall was activated earliest (Figure 1, upper left), followed by the LV septum (green colors) and then the LV lateral wall (blue color). During RV septal pacing (Figure 1, upper right), the LV septum was activated relatively early, but subsequent activation around the LV endocardium and then toward the LV lateral epicardium was slow. LV apical pacing (Figure 1, lower left) resulted in early apical activation, followed by a rapid spread of activation from LV apex to base, especially along the entire LV endocardium (see movie, Data Supplement). During LV apical pacing, the activation in the LV wall occurred synchronous in the LV lateral wall and interventricular septum, whereas the RV base was activated latest. LV septal pacing (Figure 1, lower right) led to a rapid activation around the LV endocardium, resulting in a pattern that, of all tested pacing sites, most closely resembled the pattern during normal conduction, albeit that the activation of the RV wall was moderately delayed (Figure 1). In both RV paced conditions, transseptal conduction took 43 to 55 ms (Table 1). Activation time around the LV circumference was 29 to 49 ms during RV apical, RV septal, and LV septal pacing, but was significantly shorter during LV apical pacing. LV septal pacing resulted in RV+LV as well as LV activation times that were significantly shorter than during RV apical pacing.
MRI Tagging Measurements of Strain, Dyssynchrony, and Discoordination
Examples of regional strain signals and maps of systolic shortening from each of the groups show that chronic RV septal and RV apical pacing resulted in a more heterogeneous distribution of systolic shortening in time, space, and amplitude compared with normal activation or chronic LV septal or LV apical pacing (Figure 2).
Globally, Figure 3A shows that during normal conduction ISF was 0.06±0.03, but that RV apical and RV septal pacing increased this discoordination index significantly (ISF near 0.3). In contrast, LV apical and LV septal pacing did not significantly increase ISF (≈0.1). Similarly, global mechanical dyssynchrony ranged between 100 and 150 ms during normal conduction as well as during LV septal and LV apical pacing but was twice as large during RV apical and RV septal pacing (Figure 3B).
Regionally, during normal conduction, earliest peak shortening was always observed in the lateral region and shortly thereafter (20 to 40 ms) observed in the other three quadrants (Figure 4A). A similar pattern was observed in the LV pacing groups, albeit with a slightly longer delay (40 to 60 ms). In contrast, the earliest peak shortening during RV pacing usually occurred in the septal region, whereas LV lateral peak shortening was significantly delayed.
Normal conduction resulted in a distribution of mechanical work that was mildly skewed toward the anterolateral wall. This distribution was not significantly altered in either LV pacing group (Figure 4B). However, a significant redistribution of work away from the septum toward the lateral wall was found in both RV pacing groups (Figure 4B). RV apical and RV septal pacing resulted in a significant redistribution of perfusion toward the anterolateral regions, whereas LV apical pacing led to increased septal perfusion and LV septal pacing did not significantly alter perfusion from baseline (Figure 4C).
Temporal Changes in Hemodynamics and Efficiency
At both 1 hour and 16 weeks of pacing, the 2 RV pacing modes depressed LV dP/dtmax and LV dP/dtmin as compared with baseline without changing end-systolic LV pressure (Table 2). Normalization of LV dP/dtmax to instantaneous LV pressure shows (Figure 5A) that pacing at the RV sites decreased LV contractility by ≈30% compared with baseline, whereas pacing at the LV sites did not significantly alter contractility. Similarly, τ was significantly (≈20%) prolonged (impaired relaxation) by RV pacing but not by LV pacing (Figure 5B). These differences in contractility and relaxation between pacing sites were not correlated to QRS duration, as RV apical pacing resulted in shorter QRS duration than LV apical pacing.
Table 2 shows that RV apical and RV septal pacing reduced interventricular mechanical asynchrony to more negative values than during normal conduction (RV-preceding-LV), whereas LV apical pacing resulted in the opposite shift. LV septal pacing best maintained native interventricular asynchrony. Ventricular pacing had a variable effect on absolute SW about the baseline values but consistently increased MVO2, significantly so in the RV pacing groups (Table 2; 1-hour values).
The baseline external efficiency (SW/MVO2) was approximately 0.21 (unitless). Figure 5C illustrates that this value was significantly reduced by RV apical and RV septal pacing (≈65% of baseline, P<0.05), whereas LV apical and LV septal pacing did not significantly change external efficiency).
Acute Comparative Pacing at 16 Weeks
The left 2 sets of triple bars in Figure 6A and 6B, depict that after chronic RV apical and RV septal pacing, an acute switch to LV apical pacing significantly augmented contractility (LV−dP/dtmax/Pinstant) and relaxation (τ), whereas switching to BiV pacing only improved relaxation. In the chronic LV pacing groups (right 2 sets of triple bars), an acute switch to RV apical pacing significantly impaired contractility and relaxation, whereas acute BiV pacing nonsignificantly impaired contractility and relaxation. Acute switching from LV apical to RV apical pacing decreased stroke volume significantly without significantly changing end-systolic pressure (supplemental Table).
After chronic RV apical pacing, acute LV apical and BiV pacing had little effect on external efficiency (Figure 6C). After chronic RV septal and LV septal pacing, acute LV apical pacing improved external efficiency, an increase that was significant in the LV septal pacing group. Acute switching to RV apical pacing reduced efficiency in LV paced groups. External efficiency during BiV pacing was between that of acute LV apical and acute RV apical pacing.
The present study demonstrates that in hearts with normal conduction through the ventricular myocardium, both LV septal and LV apical pacing (1) induce considerably less desynchronization of LV electric activation than RV septal and RV apical pacing, (2) maintain normal distribution of mechanical work and blood flow, mechanical synchrony, and coordination of contraction and consequently contractility, relaxation, and external efficiency over at least 4 months, and (3) appear at least as effective in minimizing desynchronization as BiV pacing.
Maintaining Synchronous Activation Using Single Pacing Sites
Although BiV pacing therapy resynchronizes the ventricles of asynchronous hearts, the primary concern during ventricular pacing of otherwise normal hearts is to prevent mechanical desynchronization. Comparison of results from large randomized clinical trials indicates that desynchronization of ventricular activation is a stronger determinant of heart failure than proper atrioventricular coupling.1
The present animal study shows that single pacing sites exist that are capable of maintaining a normal distribution of myocardial strains as well as normal hemodynamic function over several months. The only other pacing site where this is the case is the His bundle. This site is obvious, being the common rapid conduction path for both ventricles. Similar to our observations in LV apical and LV septal pacing, His bundle pacing in patients has been shown to result in better hemodynamic performance19 and more uniform distribution of perfusion when compared with RV pacing.20
The degree of blood flow redistribution during RV apical pacing is similar to that during experimental left bundle-branch block12 and is probably related to redistribution of work load and oxygen demand within the LV wall.6,12
The data from the present study extend earlier findings on the beneficial hemodynamic effects of LV septal and LV apical pacing in an acute hemodynamic study.8 In addition, it provides a mechanism for these effects, as the best pacing sites maintain a closer to normal electric activation pattern as well as mechanical synchrony and coordination. Interestingly, the 2 LV pacing sites generate a beneficial influence on the hemodynamic performance by slightly different electric activation patterns. LV septal endocardial pacing is characterized by faster activation of the entire LV, whereas during epicardial LV apical pacing the resultant synchronous contraction is predominantly due to quick engagement of the impulse into the LV endocardial layers and subsequent fast apex to base conduction along all wall segments of the LV. This fast endocardial impulse conduction is in agreement with earlier findings.21 Thirty-year-old measurements by Myerberg et al22 indicate that this high conduction velocity may be attributed at least partly to subendocardial non-Purkinje fibers.
Our promising findings on chronic LV apical pacing are in line with superior hemodynamic performance in an acute pediatric pacing study.23 Its chronic benefit was demonstrated by reversal of heart failure after switching from RV pacing to LV apical pacing in a 2-year-old patient.24 In these pediatric studies, the contraction sequence and LV pump function during single-site LV apical pacing was at least as good as that during BiV pacing.
LV Versus RV Septal Pacing
One of the most remarkable findings in the present study is the large difference in electric activation, hemodynamic effects, and distribution of both strain and blood flow between pacing at the RV and LV side of the interventricular septum. Although the RV and LV septal pacing sites were not more than ≈1 cm apart, this distance appears to be crucial for the difference between adverse effects and maintained normal function.
During RV septal pacing, the LV septal endocardium is activated ≈40 ms later, and it takes another ≈50 ms to conduct the impulse around the LV endocardium. During LV septal pacing, the transseptal conduction occurs (in rightward direction) simultaneous with the circumferential LV endocardial conduction, thus reducing total LV activation time significantly.
The considerably later mechanical activation of the LV during RV stimulation in the present study is expressed by the ≈20 ms later rise in LV pressure, whereas this timing difference was only ≈5 ms during LV septal pacing, which was similar to that during normal conduction. In addition, LV peak shortening times in the anterior and lateral walls were at least 50 ms later than that in the septal and posterior wall. Therefore, stimulating the left side of the septum significantly reduces both the interventricular and intraventricular asynchronies elicited by stimulation at the right side of the septum.
RV Apical Versus RV Midseptal Pacing
Clinically, the most studied alternative pacing sites are the RV septum and outflow tract.3 Results of acute and chronic studies show mixed results with a tendency toward better hemodynamic outcome when pacing at these alternative sites.4 However, much uncertainty is present, due to poor definition of the exact pacing site, the limited number of hemodynamic parameters studied, and nonrandomized studies. Of the 5 chronic studies referred to in Reference 4, 2 demonstrated a significant benefit of RV septal over RV apical pacing.4 In 1 of these studies, RV septal pacing produced a shorter QRS duration, whereas in the other positive study, the septum was mapped to achieve the shortest QRS duration.25,26
In the present study, the lead was implanted in the RV midseptum, based solely on position and not optimizing the QRS complex. Surprisingly, none of the parameters investigated in the present study (electric mapping, hemodynamic, regional strains, efficiency) showed a significant difference between RV apical and RV septal pacing. Similarly, no apparent benefit of RV septal pacing over RV apical pacing was observed in a clinical study of LV pressure-volume loops that also used purely anatomic lead positioning.5 A recent comparison of chronic RV apex and RV septal pacing, based entirely on lead position, showed that RV septal pacing was associated with more impaired circumferential strain (P<0.001) and worse LV dyssynchrony than apical pacing.27 Therefore, it appears that the occasionally observed beneficial effects of RV septal pacing are not achieved solely from the higher lead position on the right side of the septum, but potentially only when pacing a “sweet spot,” implying stimulation of the rapid conduction system.
Limitations and Potential Clinical Implications
Data from animal experiments should always be extrapolated to the clinic with caution. The canine hearts from the present study may differ in various respects from those of patients. In the current study, complete AV block was induced and ventricular pacing was started immediately. In the clinical situation, hearts with acquired and presumably gradually developing AV block may have undergone ventricular remodeling. Moreover, the canine hearts in the present study did not have coronary artery disease, as may be the case in patients. A benefit of our experimental approach is the possibility to investigate many variables with respect to their response to pacing site. However, statistical testing on many variables may lead to Type I errors (falsely positive significant differences), despite correction for multiple comparisons.
Despite these potential differences, adverse hemodynamic effects of RV pacing are equally clear in the human5,7,28 and canine heart.8,29 Maintaining conduction, contractile coordination, and LV pump function as close as possible to that during normal conduction, as demonstrated for LV septal and LV apical pacing over 4 months, may decrease the long-term risk of developing heart failure. After all, evidence accumulates that acute hemodynamic disturbance leads to a vicious circle of adverse myocardial remodeling1,30 and that the amount and extent of dyssynchrony is a risk factor for developing heart failure.31 Moreover, the decreased external efficiency leads to increased oxygen demand, thus reducing coronary reserve,2 which may give rise to myocardial stunning and hibernation and, consequently, further diminishment in cardiac pump function.
The present study shows that it is possible to achieve good long-term cardiac function by pacing from a single site, such as the LV apex or LV septum. Feasibility of the use of these novel alternate pacing sites clearly depends on the availability of tools for easy and safe implantation. LV apical pacing does require an open thorax or minimally invasive approach. Consequently, LV apical pacing currently is limited to children (where pacing leads are often placed epicardially) and patients undergoing surgical implantation. However, the LV apex is relatively easy to access using a subxiphoid approach, so that after development of proper tools, positioning of a pacing lead at this site could become feasible for many more patients.
In the present study, LV septal pacing was achieved using a transventricular-septal approach. This is a novel technique, allowing LV pacing while avoiding placing a lead inside the LV cavity with its associated risk of creating thromboembolic reactions. Clinical application of this approach will require further development of a proper pacing lead and guiding catheter to accurately locate the lead in a repeatable manner as well as extensive investigation of the safety of such positioning.
Although the conventional RV apex site could still be considered for pacing with normal cardiac function and structure, the use of any of the 2 studied LV pacing sites could serve as alternative to upgrading to BiV pacing or primary BiV pacing. In this case, the risk of implanting the coronary sinus lead, alone or in combination with the RV lead, should be weighed against that of positioning the LV apical or septal lead.
In contrast to RV pacing, LV apical and LV septal pacing result in moderate electric desynchronization, minor redistribution of mechanical work and perfusion, and normal levels of contractility, relaxation, and myocardial efficiency, even over 4 months of pacing. RV septal pacing does not provide a benefit compared with RV apical pacing. Single-site LV apical and LV septal pacing maintain normal cardiac function and efficiency at least as well as biventricular pacing.
We are indebted to Benjamin Paylor for his help in the microsphere analysis.
Sources of Funding
This study was supported by Medtronic, Inc (Minneapolis, Minn) and Bakken Research Center (Medtronic, Maastricht, The Netherlands).
Dr Prinzen receives research grants from Medtronic, Inc, Boston Scientific Corp (St Paul, Minn), and EBR Systems (Sunnyvale, Calif). Drs Mulligan, Skadsberg, and Cornelussen are Medtronic employees; Drs Mulligan and Skadsberg own Medtronic stock.
Knaapen P, van Campen LM, de Cock CC, Gotte MJ, Visser CA, Lammertsma AA, Visser FC. Effects of cardiac resynchronization therapy on myocardial perfusion reserve. Circulation. 2004; 110: 646–651.
de Cock CC, Giudici MC, Twisk JW. Comparison of the haemodynamic effects of right ventricular outflow-tract pacing with right ventricular apex pacing: a quantitative review. Europace. 2003; 5: 275–278.
Lieberman R, Padeletti L, Schreuder J, Jackson K, Michelucci A, Colella A, Eastman W, Valsecchi S, Hettrick DA. Ventricular pacing lead location alters systemic hemodynamics and left ventricular function in patients with and without reduced ejection fraction. J Am Coll Cardiol. 2006; 48: 1634–1641.
Nelson GS, Berger RD, Fetics BJ, Talbot M, Spinelli JC, Hare JM, Kass DA. Left ventricular or biventricular pacing improves cardiac function at diminished energy cost in patients with dilated cardiomyopathy and left bundle-branch block. Circulation. 2000; 102: 3053–3059.
Baller D, Wolpers HG, Zipfel J, Bretschneider HJ, Hellige G. Comparison of the effects of right atrial, right ventricular apex and atrioventricular sequential pacing on myocardial oxygen consumption and cardiac efficiency: a laboratory investigation. Pacing Clin Electrophysiol. 1988; 11: 394–403.
Vernooy K, Verbeek XA, Peschar M, Crijns HJ, Arts T, Cornelussen RN, Prinzen FW. Left bundle branch block induces ventricular remodelling and functional septal hypoperfusion. Eur Heart J. 2005; 26: 91–98.
Kirn B, Jansen A, Bracke F, van Gelder B, Arts T, Prinzen FW. Mechanical discoordination rather than dyssynchrony predicts reverse remodeling upon cardiac resynchronization. Am J Physiol Heart Circ Physiol. 2008; 295: H640–H646.
Verbeek XA, Vernooy K, Peschar M, Van Der Nagel T, Van Hunnik A, Prinzen FW. Quantification of interventricular asynchrony during LBBB and ventricular pacing. Am J Physiol Heart Circ Physiol. 2002; 283: H1370–H1378.
Suga H. Ventricular energetics. Physiol Rev. 1990; 70: 247–277.
Doucette JW, Corl PD, Payne HM, Flynn AE, Goto M, Nassi M, Segal J. Validation of a Doppler guide wire for intravascular measurement of coronary artery flow velocity. Circulation. 1992; 85: 1899–1911.
Vernooy K, Cornelussen RN, Verbeek XA, Vanagt WY, van Hunnik A, Kuiper M, Arts T, Crijns HJ, Prinzen FW. Cardiac resynchronization therapy cures dyssynchronopathy in canine left bundle-branch block hearts. Eur Heart J. 2007; 28: 2148–2155.
Deshmukh P, Casavant DA, Romanyshyn M, Anderson K. Permanent, direct His-bundle pacing: a novel approach to cardiac pacing in patients with normal His-Purkinje activation. Circulation. 2000; 101: 869–877.
Zanon F, Bacchiega E, Rampin L, Aggio S, Baracca E, Pastore G, Marotta T, Corbucci G, Roncon L, Rubello D, Prinzen FW. Direct His bundle pacing preserves coronary perfusion compared with right ventricular apical pacing: a prospective, cross-over mid-term study. Europace. 2008; 10: 580–587.
Frazier DW, Krassowska W, Chen PS, Wolf PD, Danieley ND, Smith WM, Ideker RE. Transmural activations and stimulus potentials in three-dimensional anisotropic canine myocardium. Circ Res. 1988; 63: 135–146.
Myerburg RJ, Gelband H, Nilsson K, Castellanos A, Morales AR, Bassett AL. The role of canine superficial ventricular muscle fibers in endocardial impulse distribution. Circ Res. 1978; 42: 27–35.
Spragg DD, Akar FG, Helm RH, Tunin RS, Tomaselli GF, Kass DA. Abnormal conduction and repolarization in late-activated myocardium of dyssynchronously contracting hearts. Cardiovasc Res. 2005; 67: 77–86.
Investigators have explored alternative pacing sites to avoid adverse clinical outcome associated with asynchronous activation and reduced left ventricular (LV) pump function induced by conventional right ventricular (RV) apex pacing. In this study in canine hearts, we investigated 3 alternative sites: RV septum, LV apex, and LV septum. LV apical and LV septal (but not RV septal) pacing maintain regional cardiac mechanics, contractility, relaxation, and efficiency near native levels over a period of 4 months. Similarity of the canine and human conduction systems suggests that the same positive effects can be expected in the human heart. LV apex pacing is beneficial in small children, in whom epicardial implantation is common practice. In adults, a minimally invasive approach seems feasible because the LV apex is relatively easy to access using a subxiphoid approach. In our animal study, LV septal pacing was achieved using a transventricular-septal approach. This novel technique avoids placing a lead inside the LV cavity with its associated risk of thromboembolic reactions. Therefore, routine clinical application of LV apical and LV septal pacing requires development of proper pacing leads and implant tools. The data also show that LV septal and LV apical pacing could serve as alternative to biventricular pacing in patients who do not tolerate RV pacing. In this case, the risk of implanting the coronary sinus lead should be weighed against that of positioning the LV apical or septal lead.
The online-only Data Supplement is available at http://circep.ahajournals.org/cgi/content/full/CIRCEP.109.882910/DC1.