Abstract
Background:
The aim of this study was to identify the ECG features that might differentiate between anterior interventricular vein (AIV) and distal great cardiac vein (d-GCV) outflow tract-ventricular arrhythmias (OT-VAs).
Methods and Results:
Radiofrequency catheter ablation was performed in 13 of 375 patients (3.5%) for AIV or d-GCV OT-VAs. We grouped the 13 patients by the origin, d-GCV (n=9) or AIV (n=4), and compared their ECGs and electrophysiological data. The OT-VA ECGs had S waves in lead I in all 13 patients. The voltage in the inferior lead III and peak deflection index showed no significant between-group differences (2.3±0.7 vs. 2.5±0.3 mV and 0.65±0.04 vs. 0.68±0.04 mV, respectively) for the d-GCV and AIV groups. There were also no significant between-group differences in the QaVL/QaVR, where Q denotes the amplitude of the Q wave in the suffix lead. However, the R/S ratio in V1 (1.7±1.0 [n=5] vs. 0.2±0.05, P=0.04), and QRS duration (149±16.6 vs. 123±3.8 ms, P=0.012) were greater in the d-GCG group than in the AIV group. There were no significant between-group differences in the activation time or pace mapping score at the optimal ablation sites.
Conclusions:
A low R/S ratio in V1 and shorter QRS duration may help identify AIV sites of epicardial OT-VA origin.
Radiofrequency catheter ablation (RFCA) is a safe and effective treatment for outflow tract-ventricular arrhythmias (OT-VAs). Approximately 1.8% of OT-VAs require ablation near the distal great cardiac vein (d-GCV).1
An even smaller percentage of OT-VAs originate from the anterior interventricular vein (AIV) and, similar to d-GCV ventricular tachyarrhythmias (VTs), are epicardial,2
but frequently difficult to ablate. The aim of this study was to identify the ECG features that might differentiate AIV from d-GCV OT-VA origin.
Methods
Study Population
RFCA of d-GCV or AIV OT-VAs was performed in 13 of 375 (3.5%) patients who underwent treatment of OT-VAs at 2 institutions. We divided these 13 patients into d-GCV (9 patients) and AIV (4 patients) groups and compared their ECG and electrophysiological study (EPS) data. All patients undergoing ablation procedures gave their written informed consent as per the institutional ethics committee requirements.
ECG Analysis
We focused on the morphology in lead I, R-wave amplitude in inferior lead III, peak deflection index (PDI),3
QaVL/QaVR, which is the ratio between the depth of the Q wave in aVL and that in aVR, R/S ratio in V1, and QRS duration in lead III as distinctive and simple ECG parameters that could possibly differentiate d-GCV from AIV origin. The PDI was determined in the inferior lead presenting the tallest R wave by dividing the time from QRS onset to the peak QRS deflection by the total QRS duration.3
The 12-lead ECG morphology of the OT VT was assessed and measured off-line using the electronic calipers in the recording system. Care was taken to ensure precision in QRS width measurement by using a uniform magnification of 100 mm/s.
EPS and Ablation
To determine the optimal ablation site, we mapped both the right and left ventricular outflow tracts (RVOT and LVOT), coronary cusps (CCs), d-GCV, and AIV. The earliest activation site was near the d-GCV in 13 patients. The pace mapping score was determined as the median value from the R/S ratio and R-wave notching in the 12-lead ECG in a blinded fashion by 3 electrophysiologists.
The GCV runs along the left circumflex artery (LCX), and the AIV runs along the left anterior descending artery (LAD). Therefore, we performed coronary angiography (CAG) to check whether the distance between the tip of the ablation catheter and the LAD was greater than 0.5–1 cm to avoid any injury to the LCX and LAD before the ablation. If we had to ablate at a site closer than 1 cm, we also performed CAG after the ablation to confirm absence of injury.
Irrigation tip catheters and/or non-irrigation tip catheters were used for the RFCA. The tip temperature of the non-irrigation tip ablation catheter in the distal GCV and AIV was maintained at 55℃ during the energy delivery for 60 s. A 4-mm electrode non-irrigation tip catheter (Blazer II, Boston Scientific Corp, Natick, MA, or Ablaze Fantasista, Japan Lifeline, Japan) was used for the RFCA. During the RFCA, the initial power was 30 W and the maximum power setting was 50 W. When the 3.5- or 4-mm tip electrode irrigated tip catheter (NAVISTAR or CELSIUS THERMOCOOL, Biosense Webster, Diamond Bar, CA, USA) was used, a power control mode with a maximum output of 40 W and temperature limit of 42℃ with an irrigation flow rate of 30 ml/min was selected.
Statistical Analysis
All values are expressed as the mean±SD and were compared by an unpaired t-test. Statistical significance was defined as P<0.05.
Results
Patients Characteristics
As
Table 1
shows, there were no differences between the 2 groups in terms of age (P=0.37), number of ventricular premature contractions (VPCs) on ambulatory monitoring (P=0.09), and left ventricular ejection fraction (P=0.27).
Table 1.
Baseline Clinical Characteristics and Ablation Data in 2 Groups of Patients Undergoing RFCA
| |
Sex |
Age (years) |
No. of VPCs |
UHD |
EF (%) |
Diameter of
the CV (mm) |
Imp. (Ω) |
No. of RF |
| Case no. (d-GCV) |
| 1 |
M |
50 |
38,464 |
HHD |
48 |
4.2 |
110 |
2 |
| 2 |
M |
23 |
Exercise |
– |
63 |
3.0 |
126 |
1 |
| 3 |
M |
52 |
31,249 |
– |
63 |
ND |
ND |
ND |
| 4 |
F |
75 |
50,619 |
– |
38 |
3.6 |
193 |
2 (Irrigation) |
| 5 |
M |
59 |
48,528 |
– |
58 |
ND |
ND |
2 |
| 6 |
F |
31 |
7,955 |
– |
65 |
ND |
ND |
3 |
| 7* |
F |
57 |
32,797 |
CM |
69 |
ND |
162 |
4 |
| 8* |
M |
76 |
23,052 |
CM |
42 |
2.6 |
170 |
5 |
| 9 |
M |
58 |
27,556 |
– |
60 |
3.4 |
169 |
3 (Irrigation) |
| Mean±SD |
|
53±18 |
32,528±13,828 |
|
56±11 |
|
155±31 |
2.8±1 |
| Case no. (AIV) |
| 10 |
M |
69 |
18,587 |
– |
68 |
3.6 |
168 |
4 (irrigation) |
| 11 |
M |
82 |
28,024 |
– |
54 |
ND |
182 |
3 (irrigation) |
| 12 |
F |
36 |
10,010 |
– |
71 |
ND |
ND |
2 |
| 13* |
M |
68 |
17,137 |
– |
60 |
ND |
ND |
0 |
| Mean±SD |
|
64±20 |
18,440±7,408 |
|
63±8 |
|
175±10 |
2.3±2 |
RFCA, radiofrequency catheter ablation; d-GCV, distal great cardiac vein; AIV, anterior interventricular vein; SD, standard deviation; No. of VPCs, number of ventricular premature contractions on 24-h ambulatory ECG recordings; UHD, underlying heart disease; HHD, hypertensive heart disease; CM, cardiomyopathy; EF, ejection fraction; CV, cardiac vein: the diameter at the optimal ablation site was measured angiographically; Imp., initial impedance at the successful ablation site; RF, radiofrequency applications; –, no UHD; ND, no data. There were no differences between the 2 groups regarding age (P=0.37), number of VPCs (P=0.09), and EF (P=0.27). *RFCA was unsuccessful in Cases 7 and 8 of the d-GCV group, and was not attempted in Case 13.
The ECGs exhibited S waves in lead I in the 13 patients. The voltage in inferior lead III and the PDI showed no significant between-group differences (2.3±0.7 vs. 2.5±0.3 mV, and 0.65±0.04 vs. 0.68±0.04 mV, for the d-GCV and AIV groups, respectively). The QaVL/QaVR in the d-GCV group was not significantly greater than that in the AIV group (Table 2). The R/S ratio in V1 was 1.7±1.0 (n=5) vs. 0.2±0.05 (n=3) (P=0.04), and the QRS duration was 149±16.6 vs. 123±3.8 ms (P=0.012) in the d-GCV and AIV groups, respectively (Table 2). There were no significant between-group differences in the activation time or pace mapping score at the optimal ablation sites (Table 3).
Table 2.
(A) ECG Findings in Both Groups of Patients Undergoing RFCA and (B) Comparison of the ECG Findings of Both Groups
| (A) |
R voltage in lead III (mV) |
R/S in V1 |
QRS (ms) |
QaVL/QaVR |
PDI |
| Case no. (d-GCV) |
| 1 |
1.8 |
R |
165 |
2.27 |
0.68 |
| 2 |
3 |
R |
160 |
1.63 |
0.71 |
| 3 |
2.6 |
0.41 |
120 |
1.40 |
0.63 |
| 4 |
2.5 |
3 |
140 |
1.43 |
0.58 |
| 5 |
1.7 |
R |
140 |
1.20 |
0.68 |
| 6 |
2.3 |
2 |
130 |
1.60 |
0.67 |
| 7 |
3.5 |
2.3 |
164 |
1.90 |
0.61 |
| 8 |
1.5 |
1 |
160 |
1.17 |
0.63 |
| 9 |
1.5 |
R |
160 |
1.00 |
0.63 |
| Mean±SD |
2.3±0.7 |
1.7±1.0 |
149±16.6 |
1.51±0.4 |
0.65±0.04 |
| Case no. (AIV) |
| 10 |
2.8 |
0.21 |
128 |
0.97 |
0.7 |
| 11 |
2.6 |
QS |
124 |
1.45 |
0.69 |
| 12 |
2.1 |
0.15 |
120 |
1.07 |
0.72 |
| 13 |
2.6 |
0.25 |
120 |
1.28 |
0.62 |
| Mean±SD |
2.5±0.3 |
0.2±0.05 |
123±3.8 |
1.19±0.2 |
0.68±0.04 |
| (B) |
Voltage in lead III (mV) |
R/S ratio in V1 |
QRS duration (ms) |
QaVL/QaVR |
PDI |
| d-GCV |
2.3±0.7 |
1.7±1.0 |
149±16.6 |
1.51±0.4 |
0.65±0.04 |
| AIV |
2.5±0.3 |
0.2±0.05 |
123±3.8 |
1.19±0.2 |
0.68±0.04 |
| P value |
0.50 |
0.04* |
0.012* |
0.16 |
0.18 |
If no S wave in V1, the R/S in V1 was not calculated. *Significant P values. PDI, peak deflection index. Other abbreviations as in Table 1.
Table 3.
Comparison of the Electrophysiological Data at the Optimal Ablation Site in Both Groups of Patients Undergoing RFCA
| |
Activation time (ms) |
Pace mapping score |
| d-GCV |
42±14 |
11.3±0.7 |
| AIV |
34±6 |
11.5±0.6 |
| P value |
0.26 |
0.7 |
Abbreviations as in Table 1.
Specific examples of the ECGs of the VPCs and pace mapping in the 2 groups are shown in
Figure 1. Note the QRS in the V1 lead. In the d-GCV group, the R/S ratio in V1 was 3.0 in Case 4 and in Case 9 there were no S waves, but a tall R wave was noted. In contrast, a QS pattern, which meant there was no R wave in V1, was seen in Case 11, and the R/S ratio in V1 was small at 0.25 in Case 13 in the AIV group. The quality of the pace mapping served to confirm the accuracy of the localization in all 4 cases.
In Case 10 in the AIV group, the OT-VA ECGs from both the AIV and d-GCV were recorded by pace mapping from the successful ablation site (Figure 2). This may be related to shifting of the tip of the ablation catheter during breathing. In the limb leads, there was an RS pattern in lead I, and lower and wider R waves in the inferior leads in the middle portion, which meant d-GCV pacing (Figure 2A). On the other hand, there was a shallow S in lead I and taller and narrower R wave in the inferior leads in the AIV pace on the right side (Figure 2A). In the chest leads, there was an RS in V1 and taller R wave in V2 in the 1st
and 2nd
beats of the pace mapping (Figure 2B); however, there was an rS in V1 and V2 in the AIV pacing (Figure 2B). Distal GCV pacing (Figure 3A, left side) created a high R/S ratio in V1, which meant a right bundle branch block (RBBB) pattern, and the local ventricular electrogram was almost equal in amplitude to the atrial electrogram at that site (Figure 3A). AIV pacing created a low R/S ratio in V1, and narrower QRS, and the local ventricular electrogram was greater in amplitude than the atrial electrogram at that site (Figure 3B).
The R/S ratio in V1 and width of the QRS complex were not helpful in discriminating between PVCs with an endocardial mitral annulus (MA) origin or from either of the epicardial origins. To do that, the PDI was better. For example, an epicardial anterior MA origin, which meant a d-GCV origin, could be differentiated from an endocardial anterior MA origin using the PDI. If the PDI was >0.6, the origin was epicardial; for example, in Case 2, the PDI at the successful site was 0.71, and that on the opposite side at an endocardial site was 0.54.
We noted that OT-VAs could not be induced with programmed stimulation in any of our 13 patients.
Ablation
Of the 6 cases in which the diameter of the coronary vein at the optimal ablation site was measured, RFCA was successful in 5 cases in which the diameter was ≥3 mm (Table 1). The percentage of cases in which the irrigated catheter was used differed between the 2 groups, so we could not simply compare the initial impedance at the successful ablation site and number of RF applications. However, they did not exhibit any significant differences.
In Case 13 in the AIV group, we performed CAG just before attempting RFCA and the optimal ablation site was too close to the LAD to perform the ablation. RFCA was unsuccessful in 2 cases in the d-GCV group (Cases 7 and 8), because the impedance was too high to perform it. In both cases, the impedance was greater than 150 ohm with a non-irrigation tip catheter. In Cases 4 and 9 in the d-GCV group, and Cases 10 and 11 in the AIV group, an irrigation tip catheter was used.
Figure 4
shows the fluoroscopic image (Figure 4A) and EPS data (Figure 4B) at the successful ablation site in Case 10. RFCA was successful in 10 of the 13 cases. Those 10 patients remained free from arrhythmias without any anti-arrhythmic drugs during a follow-up period of 58±41 months. As for the remaining 3 patients, 200 mg of flecainide was started in Case 13 in the AIV group, β-blockers were continued and the symptoms improved in Case 7, and a surgical epicardial ablation was performed successfully in Case 8.
Discussion
Main Findings
When the optimal ablation site is in the AIV, the impedance is often too high to perform RFCA, sometimes necessitating an epicardial approach.4,5
In contrast, in the d-GCV, which is downstream of the AIV, it is frequently possible to achieve successful ablation because of the greater diameter at the d-GCV than that at the AIV. Therefore, knowing the ECG characteristics that could differentiate between OT-VAs originating from the AIV and d-GCV would be very useful in planning the ablation strategy. Our study suggested that the R/S ratio in V1 and the QRS duration in the inferior leads may help identify the site of origin as either the AIV or d-GCV. The existence of S waves in lead I in the 13 study patients suggested that the d-GCV and AIV OT-VAs originated from the left-sided ventricle or ventricular septum.
The OT-VAs in the d-GCV group were similar to the OT-VAs from the endocardial MA with respect to the ECG morphology and anatomical features.6,7
This was because the d-GCV is located on the epicardial side of the MA.8
In fact, the data for OT-VAs from the endocardial MA in the previous reports6,7
exhibit an R/S ratio in V1 as high as that in the d-GCV group. One reason we calculated the PDI in the current study was that the OT-VAs in the d-GCV group could be differentiated from those from the endocardial MA by the PDI.3
It is believed that OT-VA origin might be from the epicardial LVOT away from the CCs when the activation time in the AIV is greater than that from any other site including the CCs.9
However, Jauregui-Abularach et al recently reported that successful ablation might be achieved from the left CC if the distance from that cusp to the earliest activation site near the junction between the AIV and the d-GCV is shorter than 13.5 mm and the Q-wave ratio is less than 1.45 in aVL/aVR, even if the earliest activation site is at the proximal AIV or the d-GCV.10
In the current study, the number of cases in which the Q-wave ratio was less than 1.45 in aVL/aVR was 5 of 9 (56%) in the d-GCV group and 3 of 4 (75%) in the AIV group. We did not try to perform RFCA in those patients whose QaVL/QaVR was less than 1.45, because the activation and pace mapping were better in the d-GCV or AIV than in the CCs and the distance was greater than 13.5 mm. RFCA was attempted at the left CC in Case 2 in the d-GCV group (Table 2) because the distance was 12 mm (<13.5 mm), but the QaVL/QaVR was 1.63. However, we could not achieve successful ablation at the left CC. In the case reported by Hirasawa et al,11
the distance from the left CC to the successful ablation site in the AIV was not mentioned, but the QaVL/QaVR was approximately 1 and the successful ablation site was not on the left CC, but in the AIV. The activation time of the AIV preceded that of the left CC by 16 ms in that case.
Mechanism of the ECG Difference Between OT-VAs Originating From the AIV and the d-GCV
Anatomically, the AIV is a tributary of the d-GCV (Figure 5,
Left panel). The origins in the d-GCV tended to be epicardial sites close to the MA, whereas those in the AIV tended to be high on the ventricular septum (Figure 5,
Right panel). This is likely why OT-VAs originating from the d-GCV displayed an RBBB pattern (ie, high R/S ratio in V1), and OT-VAs originating from the AIV result in a narrower QRS than those originating from the distal GCV. Although the QaVL/QaVR ratio in the d-GCV group was not significantly greater (P=0.16) than that in the AIV group (Table 2B), there is a chance that a larger study may demonstrate that the origins of the d-GCV group tend to be on the left side compared with those of the AIV group.
ECG Difference Between OT-VAs Originating From the AIV and the Septal RVOT
It is sometimes difficult to differentiate between OT-VAs originating from the AIV and those originating from the septal RVOT by ECG alone. However, a previous study indicated that when the PDI is used, an AIV origin can be identified, because the AIV origin leads to a PDI >0.6 because of its epicardial origin.3
An exception to this rule occurs when the septal RVOT origin is deep inside the ventricular septum, because the PDI could also be >0.6 in that case.3
Kurosaki et al reported that malignant arrhythmias from the RVOT, although rare, should be considered when the patient has a syncopal episode and VPCs with a positive QRS complex in lead I.12
Although we have not described RVOT-VAs, but rather epicardial OT-VAs, there were no cases of a distinctive positive QRS complex in lead I.
Unsuccessful RFCA
In Cases 7 and 8 of the present study, the impedance was too high to perform RFCA even though the site was optimal with respect to the pace mapping. Yamada et al reported a similar case in which ablation was abandoned because of inaccessibility of the catheter to the myocardium or a high impedance during the RF application within the GCV.13
Although we used a 5Fr ablation catheter first in Case 9, the impedance was too high to deliver the RF energy. In that case successful ablation was achieved with an irrigated catheter. The benefit, of course, was the use of the irrigation system with the irrigated catheter as compared with the smaller catheter. On the other hand, in Case 2 from the d-GCV group, the RFCA was unsuccessful with both a 4-mm electrode tip non-irrigated and 4-mm electrode tip irrigated catheter, forcing us to use a 5Fr ablation catheter (Life-line Japan), which lowered the impedance to 126 Ω, and resulted in successful RFCA. A small sized coronary vein at the optimal ablation site seemed to be a factor in the unsuccessful RFCA procedures. When the diameter at the optimal ablation site was not greater than 3 mm, the impedance was too high to perform RFCA. Therefore, CAG should be performed and the diameter of the d-GCV or AIV in the venous phase should be checked, and coronary venography is sometimes needed to measure the diameter at the optimal ablation site. The manner in which the ablation catheters in Cases 9 and 2 were used showed which ablation catheter was better than the other, and it seemed to depend on the individual case.
Although a surgical epicardial ablation was performed successfully in Case 8, we did not use a nonsurgical transthoracic epicardial approach in the unsuccessful RFCA cases from the d-GCV and AIV groups. That was because epicardial fat is concentrated in the interventricular grooves and along the major branches of the coronary arteries,14
which would include the d-GCV and AIV, and we believed the presence of epicardial fat would hinder the performance of RFCA.
Importance of CAG
We think that CAG is essential for successful ablation of OT-VAs originating from the AIV and d-GCV, because coronary arterial injury from RFCA must be avoided.15
Takahashi et al reported a case of acute occlusion of the LCX during catheter ablation in the coronary sinus while completing a linear lesion between the MA and left inferior pulmonary vein for the treatment of atrial fibrillation.16
Although that report was not about OT-VAs, it emphasizes the fact that coronary arteries may become occluded when RF energy is delivered to a vein that runs along the coronary artery.16
The GCV runs along the LCX, and the AIV runs along the LAD.
Arrhythmia Mechanism
In our 13 patients, the OT-VAs could not be induced with programmed stimulation. This was true for the 3 patients with underlying heart disease, as well as the 10 patients without underlying heart disease, and we interpreted the mechanism of OT-VAs as non-reentrant. Conversely, VT that can be reproducibly induced with programmed stimulation and can be entrained, such as in non-ischemic cardiomyopathy, suggests reentry as the underlying electrophysiologic mechanism.17
It is possible that our patients with underlying heart disease had an arrhythmogenic substrate, despite the non-inducibility of VA, but we did not perform confirmatory CT scan or MRI.
Study Limitations
The anatomical relationship of the AIV, d-GCV, and ventricular septum, including the RVOT side, is highly variable among patients. Therefore, in some patients, the AIV may not adhere to the entire ventricular septum. ECGs are also influenced by factors such as the position of the patient’s heart and thoracic shape. Therefore, these ECG criteria for differentiating OT-VAs originating from the AIV from those originating from the d-GCV cannot be perfect. A larger study would be helpful in determining the best cut-off values for the R/S ratio and QRS complex width.
Conclusions
Although the AIV follows the d-GCV anatomically, the R/S ratio in V1 and QRS duration may identify the site of origin as being either the AIV or d-GCV. The knowledge of these ECG characteristics may help to obtain successful ablation of epicardial OT-VAs that have a d-GCV or AIV origin.
Conflict of Interest
None declared.
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