Introduction
Key Teaching Points
•
Three-dimensional voltage gradient mapping can help identify the slow pathway.
•
Etripamil is a novel short acting L-type calcium channel blocker effective in terminating
supraventricular tachycardia by primarily affecting atrioventricular nodal conduction.
We report on the electroanatomic characteristic changes of the slow pathway region
using high-density voltage gradient mapping on 1 subject during phase II testing of
NODE-1.
•
Voltage gradient mapping of the atrial septum in the triangle of Koch has been reported
as a method of identifying the slow pathway region to target for ablation.
High-density (HD) mapping of tachycardias can be helpful in identifying the circuits
in complex arrhythmias. It has also been shown to be helpful in identifying the slow
pathway in atrioventricular nodal reentrant tachycardia (AVNRT). We participated in
the NODE-1 study, which was a multicenter, placebo-controlled, double-blinded, dose-ranging
phase II study comparing 4 doses of intranasal Etripamil to placebo for the conversion
of induced supraventricular tachycardia.
1
Etripamil (Milestone Pharmaceuticals Inc, Montreal, Quebec, Canada) is a novel short-acting
L-type calcium channel blocker effective in terminating supraventricular tachycardia
by primarily affecting AV nodal conduction. During testing on 1 of the subjects, serial
high-density mapping of the slow pathway region was performed.
Case report
A 62-year-old woman with recurrent documented narrow complex tachycardia presented
for radiofrequency ablation. She was consented to the NODE-1 study. The study was
approved by our local Investigational Review Board.
A routine electrophysiology study was performed. Josephson fixed curve quadripolar
catheters (Response, St. Jude Medical, Minnetonka, MN) were placed in the right atrium
and the right ventricle. A steerable decapolar catheter (Livewire, St. Jude Medical,
Minnetonka, MN) was placed in the coronary sinus (CS) and used as a reference catheter.
A 2-2-2-mm spaced steerable octapolar catheter (Biosense Webster, Diamond Bar, CA)
was placed in the His bundle region. Before induction of tachycardia, HD mapping along
with 3-dimensional mapping of the right atrial septum around the slow pathway region
was performed with the octapolar catheter and the EnSite Velocity system (St. Jude
Medical, St Paul, MN). Baseline measurements were made. AV node Wenckebach was 330
ms. During AV node effective refractory period determination, there was a jump from
the fast to the slow pathway and tachycardia was induced with a cycle length of 373
ms. Septal VA time was 61 ms and ventricular overdrive pacing just below the cycle
length of the tachycardia induced a V-A-V response with a tachycardia cycle length
> 110 ms, all consistent with typical AVNRT.
Once tachycardia was confirmed to be AVNRT, the patient was randomized in the NODE-1
protocol. The protocol specifies that the tachycardia be sustained for 5 minutes and
then study drug given via intranasal route. Within 90 seconds after inhalation of
the study drug, tachycardia terminated. At predetermined time points required in the
study (3, 15, and 30 minutes post drug inhalation) pacing maneuvers were attempted
and additional HD mapping of the slow pathway region was also repeated with the octapolar
catheter.
HD mapping was not part of the NODE-1 protocol but is routinely performed in our AVNRT
cases at our center. With the 2-mm spaced octapolar catheter, we manually obtained
and annotated multiple points at each location in the atrial septum. An average of
1154 points were collected (range, 820–1375) and 489 points annotated (range, 384–624)
to create the maps. By manually adjusting the voltage setting in cases with a slow
pathway, a low-voltage bridge can be noted in the slow pathway region reaching from
below the level of the CS os toward the compact AV node.
2
This low-voltage atrial signal represents the fractionated electrogram, which can
be targeted for ablation (Figure 1).
Figure 1
Baseline sinus rhythm voltage map. Image is left lateral view. Adjustment of the voltage
settings show heterogeneous colors (between red and yellow), which represent the low-voltage
bridge (slow pathway). This area is between areas of no voltage (gray) and high voltage
(purple). Yellow dots represent the His region. CS = coronary sinus.
To create a voltage gradient map to identify the slow pathway bridge, the high voltage
is set at 1.5 mV and dynamically adjusted. Then the minimum voltage value is dynamically
adjusted from 0.1 mV until a compressed band of heterogeneous colors appears between
the spectrum of red and yellow. The values below the lower value will display as gray
and voltages above maximum value will be purple. All maps displayed in the figures
use the same voltage gradient values. The low-voltage bridge is the area of heterogeneous
color compression (between red and yellow), which may be between 2 gray areas representing
an area of tissue that has higher signals than its surrounding area, or it may represent
a narrow band of compressed colors between the gray area (low-voltage signals) and
the purple area (high-voltage signals). This low-voltage bridge has been shown to
correlate with slow pathway function.
2
Atrial pacing down to AV block cycle length was performed at the prespecified time
points (3, 15, and 30 minutes). There was a marked change in the AV block cycle length
from baseline of 330 ms to 550 ms 3 minutes after inhalation of Etripamil. Figure 2A
shows loss of the voltage in the slow pathway region at 3 minutes post inhalation.
There was gradual improvement in the block cycle length from 490 ms down to 450 ms
at 15 and 30 minutes, respectively. Correlating to the improvement in block cycle
length, there is return of voltage in this area, as shown in Figures 2B and 3A.
Figure 2
Etripamil sinus rhythm voltage maps. A: Voltage map 3 minutes after Etripamil showing
loss of low-voltage bridge voltage. B: Sixteen minutes post Etripamil showing return
of voltage in the low-voltage bridge region. CS = coronary sinus.
Figure 3
Postablation sinus rhythm voltage maps. A: Thirty-one minutes post Etripamil showing
the low-voltage bridge. White dots (short test lesions without junctional beats) and
blue dots (successful lesions with junctional beats) showing where radiofrequency
lesions were delivered. B: Thirty minutes post ablation showing loss of low-voltage
bridge, which appears similar to Figure 2A, which was 3 minutes post Etripamil. CS
= coronary sinus.
After 45 minutes, catheter ablation of the slow pathway was performed using a 4-mm
Safire ablation catheter (St. Jude Medical, Minnetonka, MN) delivering up to 30 W,
50°C for 60 seconds, targeting the low-voltage bridge in Figure 3A. Junctional beats
were noted in the area predicted by our voltage map. After a 30-minute waiting period,
tachycardia could not be induced post ablation with or without isoproterenol infusion,
and HD mapping was again performed. Figure 3B shows loss of the bridge and the lack
of voltage 30 minutes post ablation in this area.
2
Discussion
We report on the electroanatomic effects of intranasal Etripamil on the slow pathway.
HD noncontact mapping of the AVNRT circuit has been previously reported.
3
Voltage mapping of the atrial septum has also been reported to be another method of
identifying the slow pathway.3, 4 In patients with AV node reentry, with adjustments
in the voltage settings, a discrete low-voltage channel appears in the low posterior
atrial septum near the CS os leading toward the compact AV node. Within the low-voltage
bridge, typical slow pathway electrograms can be seen. When this area is successfully
ablated, the voltage map changes and there is no longer a low-voltage bridge noted
in this region.
Etripamil is a L-type calcium channel blocker with a short half-life (<5 minutes).
After the study was completed, we were able to confirm that the patient received Etripamil
105 mg and not placebo. Serial HD voltage maps taken over the next several minutes
after medication administration shows the dramatic effects that Etripamil has on the
slow pathway region. Immediately post inhalation at 3 minutes, the map shows a dramatic
loss of voltage in the slow pathway (Figure 2A) similar to the postablation map (Figure 3B),
suggesting that Etripamil affects the slow pathway bridge. Over the next several minutes,
there is a gradual recovery of voltage in this area along with slow recovery of AV
nodal conduction (Figures 2B and 3A). The voltages surrounding tissue in the CS region
and fast pathway region do not seem to be affected as much. Unfortunately, this was
the only case in which we were able to perform HD mapping post Etripamil inhalation,
because the study closed shortly afterward. Further studies should be performed to
evaluate the slow pathway with this medication.