Optimized Left Ventricular Endocardial Stimulation Is Superior to Optimized Epicardial Stimulation in Ischemic Patients With Poor Response to Cardiac Resynchronization Therapy: A Combined Magnetic Resonance Imaging, Electroanatomic Contact Mapping, and Hemodynamic Study to Target Endocardial Lead Placement

Abstract

Objectives: The purpose of this study was to identify the optimal pacing site for the left ventricular (LV) lead in ischemic patients with poor response to cardiac resynchronization therapy (CRT).

Background: LV endocardial pacing may offer benefit over conventional CRT in ischemic patients.

Methods: We performed cardiac magnetic resonance, invasive electroanatomic mapping (EAM), and measured the acute hemodynamic response (AHR) in patients with existing CRT systems.

Results: In all, 135 epicardial and endocardial pacing sites were tested in 8 patients. Endocardial pacing was superior to epicardial pacing with respect to mean AHR (% change in dP/dt_max vs. baseline) (11.81 [-7.2 to 44.6] vs. 6.55 [-11.0 to 19.7]; p = 0.025). This was associated with a similar first ventricular depolarization (Q-LV) (75 ms [13 to 161 ms] vs. 75 ms [25 to 129 ms]; p = 0.354), shorter stimulation-QRS duration (15 ms [7 to 43 ms] vs. 19 ms [5 to 66 ms]; p = 0.010) and shorter paced QRS duration (149 ms [95 to 218 ms] vs. 171 ms [120 to 235 ms]; p < 0.001). The mean best achievable AHR was higher with endocardial pacing (25.64 ± 14.74% vs. 12.64 ± 6.76%; p = 0.044). Furthermore, AHR was significantly greater pacing the same site endocardially versus epicardially (15.2 ± 10.7% vs. 7.6 ± 6.3%; p = 0.014) with a shorter paced QRS duration (137 ± 22 ms vs. 166 ± 30 ms; p < 0.001) despite a similar Q-LV (70 ± 38 ms vs. 79 ± 34 ms; p = 0.512). Lack of capture due to areas of scar (corroborated by EAM and cardiac magnetic resonance) was associated with a poor AHR.

Conclusions: In ischemic patients with poor CRT response, biventricular endocardial pacing is superior to epicardial pacing. This may reflect accessibility to sites that cannot be reached via coronary sinus anatomy and/or by access to more rapidly conducting tissue. Furthermore, guidance to the optimal LV pacing site may be aided by modalities such as cardiac magnetic resonance to target delayed activating sites while avoiding scar.

Keywords: AHR, acute hemodynamic response; CMR, cardiac magnetic resonance; CRT; CRT, cardiac resynchronization therapy; EAM, electroanatomic mapping; LV, left ventricle/ventricular; LVendo, left ventricular endocardium; LVepi, optimal epicardial response; LVepi1, implanted LV lead; LVepi2, temporary LV lead; Q-LV, first ventricular depolarization; cardiac magnetic resonance imaging; electroanatomic map; endocardial pacing.

Graphical abstract

Figure 1

Fluoroscopic and Electroanatomic Imaging of the Study Protocol (A) Fluoroscopic image of the invasive protocol. (B) Corresponding electroanatomic endocardial, contact scar map using a decapolar left ventricular (LV) catheter and the EnSite Velocity NavX system (St. Jude Medical, Inc., St. Paul, Minnesota); right anterior oblique (left) and left anterior oblique (right) projections. Data points with a sensed electrogram amplitude of <0.5 mV were defined as scar (grey), those with voltage of >1.5 mV were defined as healthy tissue (purple) and those points in between were in the scar border zone with a color range. The anterior surface of the heart in the left panel has been removed to see the location of the endocardial catheter (green) and distal tip (green circle). The epicardial pacing (LVepi)2 lead is in an anterior vein and displayed in blue on the EAM. In addition, the position of the implanted (LVepi)1 lead is shown on fluoroscopy and has been superimposed on the electroanatomic map in both views. Epi = epicardial pacing; HRA = high right atrial; LVEndo = endocardial pacing; RA = right atrial; RADI = LV pressure wire; RV = right ventricular.

Figure 2

Electroanatomic Contact Scar Map With Associated Acute Hemodynamic Responses During Biventricular Pacing at Different Sites Anteroposterior (left) and left anterior oblique (right) projections. Data points with a sensed electrogram amplitude of <0.5 mV were defined as scar (grey), those with voltage >1.5 mV were defined as healthy tissue (purple), and those points in between were in the scar border zone with a color range. The best epicardial (LVepi1 and LVepi2) acute hemodynamic response (% change in dP/dt, mm Hg compared with baseline during biventricular pacing) is displayed alongside 5 endocardial (LVendo) positions. Abbreviations as in Figure 1.

Figure 3

The Optimal Site for LV Stimulation During Biventricular Pacing Optimal endocardial (left) and epicardial (right) sites (by acute hemodynamic response [AHR]) for placement of the LV lead in the 8 patients. Black circles with a yellow circumference represent the best overall location (LVendo vs. LVepi). This demonstrates that in 6 patients, LVendo pacing produced the best AHR and the optimal locations were dispersed throughout the geometry of the LVendo. Two patients had the best AHRs achieved with LVepi pacing; as can be seen the pacing locations were clustered due to the constraints of the epicardial veins. AHA = American Heart Association; ANT = anterior; ANT LAT = anterior lateral; POST = posterior; POST LAT = posterior lateral; SEPT = septal; other abbreviations as in Figure 1.

Figure 4

Local Activation Map, Correlation With Myocardial Fibrosis on CMR and Associated AHR at Different Locations in 1 Patient (Top) Electroanatomic (EAM) contact map showing local activation in the same subject as in Figure 2. White signifies earliest activation and blue latest activation, demonstrating the basal lateral region as the site of latest electrical delay. In this case, the optimal AHR (star) matched the site of latest electrical delay, which was distant from ischemic scar. (Bottom) Cardiac MR (CMR), late gadolinium enhancement sequences in the short axis, mid ventricular (left), 2-chamber (middle), and 4 chamber (right) views. The white arrows demonstrate areas of thin walled myocardium with associated subendocardial myocardial fibrosis, corresponding to an left anterior descending (LAD) territory myocardial infarction. There is a close correlation between the scar demonstrated on the EAM and that displayed with CMR. (Right) AHA bulls-eye plot diagram with scar (derived from CMR and EAM) spray painted in grey (anterior, LAD infarct). All different positions for the LV lead are demonstrated (both epicardial and endocardial) with the legend detailing whether the associated AHR with biventricular pacing was <10% or >10% improvement from baseline. Pacing around the anterior regions of scar corresponded to a poor AHR, compared with much better AHRs in sites out of scar. Abbreviations as in Figures 1 and 3.

Figure 5

Local Activation Map and Associated Acute Hemodynamic Response in a Patient With Electrical Latency Within a Large Area of Scar Dilated, globular heart with a heavy burden of myocardial scar. Earliest activation is white and latest activation blue/purple. In this case, LVendo locations were not superior to conventional LVepi with respect to the AHR. The point of latest electrical activation in this case is around the anteroseptum, most likely as a result of slow activation spreading and encircling a large region of scar. Although these sites are the latest activated they will not produce a good AHR because they are in scar and may explain why the latest activated site is not always the optimal pacing site. Abbreviations as in Figures 1 and 3.