Left-to-right shunting PDA is one of the most commonly recognized congenital diseases in dogs.1,2 Substantial left-to-right shunting can lead to pathological pulmonary overcirculation and volume overload of left-sided cardiac structures, potentially resulting in congestive heart failure. If PDA occlusion is not performed, 64% of affected dogs die within 1 year.1 Treatment of this disease involves permanent attenuation of ductal flow, either through SL or minimally invasive transcatheter occlusion with devices such as CDOs, vascular plugs, or embolization coils implanted via an arterial or venous approach.3–5
Surgical ligation techniques include standard dissection and circumferential ligation, application of hemoclips,6 oversewing the ends of a transected ductus,7 the Jackson-Henderson dissection technique,8 and an intrapericardial dissection technique.9 Surgical ligation can be curative when performed at an early age in dogs without clinical signs of heart failure,10 with a high overall success rate.11 The most serious complication associated with surgical dissection and ligation is potentially fatal hemorrhage, which has occurred in 1% to 17% of dogs treated with this technique1,7,12,13 and has been associated with mortality rates ranging from 0% to 7%.7,10,11
Among the minimally invasive treatment approaches, transcatheter occlusion with a CDO device has been reported as the treatment of choice for dogs with left-to-right shunting PDA. The CDO is superior to other minimally invasive devices because CDO implantation is associated with a low complication rate (as low as 3%) and achieves complete cessation of ductal flow, with a reported success rate of 92%.5 Potential major complications associated with all transarterial devices include dislodgement or embolization of the device into an unintended location, inadvertent damage to the aorta or other major blood vessels leading to hemorrhage, and ductal reopening through the device.14 The overall embolization rate when a CDO is used is low relative to that when embolization coils are used.5,15
Several studies11,16,17 have been reported in which outcomes were compared between SL and minimally invasive transcatheter techniques for the treatment of dogs with left-to-right shunting PDA. However, these studies all included coil embolization as a transcatheter technique. In 1 study,11 comparison between SL and transarterial coil occlusion revealed that SL was more successful overall (94%) but carried a higher rate of major complications (12%), whereas transarterial coil occlusion had a lower initial success rate (84%) but fewer complications overall (4%).
At the authors' institution, CDO implantation is the preferred technique for PDA closure when feasible owing to its minimally invasive nature, low complication rate, and effectiveness. In addition, SL is preferred to transarterial coil embolization for dogs ineligible for CDO implantation; however, objective data to support this clinical practice are lacking.
To the authors' knowledge, no direct comparison of outcomes between CDO implantation and SL outcomes has been reported in the peer-reviewed veterinary literature. The primary objective of the study reported here was to compare short-term major complications and rate of survival to hospital discharge between the 2 methods for the treatment of dogs with left-to-right shunting PDA. We hypothesized that dogs treated with SL would have a significantly greater rate of major intraoperative complications and lower rate of survival to hospital discharge than dogs treated with CDO implantation.
Materials and Methods
Animals
Electronic medical records of canine patients at the Oregon State University Veterinary Teaching Hospital from January 1, 2006, to October 31, 2016, were searched to identify those that had received an echocardiographic diagnosis of left-to-right shunting PDA by a board-certified veterinary cardiologist and were subsequently treated with SL or CDO implantation. All surgeries and transarterial procedures had been performed or directly supervised by a board-certified veterinary surgeon or cardiologist, respectively. No specific exclusion criteria were applied. Included dogs were grouped by whether they had been treated by SL (SL group) or CDO implantation (CDO group).
Medical records review
Preoperative data—Preoperative data collected from each dog's medical records included breed, sex and neuter status, age and body weight at the time of ductal occlusion, and clinical signs potentially related to the PDA (eg, coughing or dyspnea). Whether the dog had any concurrent cardiac congenital defects or left-sided congestive heart failure was noted. All thoracic radiographs from the time of diagnosis were reviewed by the same investigator (BR), and cardiac size was measured with the VHS method.18 Echocardiographic measurements collected from the medical record included LVIDd, LVIDs, LA:Ao, fractional shortening, and subjective scoring of the presence and severity of mitral valve regurgitation (none [0], trace [1], mild [2], moderate [3], or severe [4]). The LVIDd and LVIDs measurements were normalized to body weight per principles of allometric scaling by use of the formulas LVIDd/(BW)0.33 and LVIDs/(BW)0.33, respectively.19 Whether any arrhythmias had been diagnosed by electrocardiography and whether those arrhythmias were malignant were recorded. Preoperative administration of cardiac medications such as diuretics (eg, furosemide), inodilators (eg, pimobendan), and angiotensin-converting enzyme inhibitors (eg, enalapril) was also recorded.
Intraoperative data—All SL procedures were performed via a left fourth intercostal thoracotomy approach and standard circumferential double-ligation with silk suture material as described elsewhere,1 unless reported otherwise. All minimally invasive procedures were performed by use of a specific CDO devicea via femoral arteriotomy with fluoroscopy guidance as described elsewhere.3
Intraoperative data extracted from the medical records included anesthetic status (American Society of Anesthesiologists status I through V, with higher scores indicating increased anesthetic risk20), duration of surgical procedure (from time of skin incision to placement of the final skin suture for the SL group, and from beginning of transesophageal echocardiography to the final skin suture for the CDO group), duration of fluoroscopy (CDO group only), and duration of anesthesia. The nature of any intraoperative complications was recorded, including any hypotension (arterial blood pressure < 70 mm Hg as measured by Doppler ultrasonic flow detector) or arrhythmias, including bradycardia (heart rate < 50 beats/min). Use of vasopressors (eg, dopamine or dobutamine), antiarrhythmic drugs (eg, lidocaine), and parasympatholytics (eg, atropine or glycopyrrolate) was also recorded.
For dogs in the SL group, major intraoperative complications were recorded and classified as hemorrhage from a major blood vessel (eg, aorta, pulmonary artery, or ductus arteriosus), any method of ductal attenuation other than standard surgical dissection with circumferential double ligation, inadvertent injury to surrounding tissues requiring an additional procedure, failure of ductal ligation requiring another surgical attempt, cardiopulmonary arrest, and death or euthanasia. For dogs in the CDO group, major intraoperative complications were recorded as device dislodgement or embolization, arterial vessel perforation, cardiopulmonary arrest, and death or euthanasia. For dogs in both groups, the nature of any other concurrently performed procedures was recorded. Dogs for which CDO implantation failed that subsequently had SL performed were also identified.
Postoperative data—All dogs were assessed for residual ductal flow by echocardiography the day following SL or CDO implantation. Noted residual ductal flow was subjectively classified as none, trivial, mild, moderate, or severe by a board-certified veterinary cardiologist. Postoperative administration of diuretics, inodilators, or angiotensin-converting enzyme inhibitors was recorded. Rate of survival to hospital discharge was determined for both groups. Details regarding any dog that failed to survive to discharge were documented and investigated.
Statistical analysis
Data were analyzed and statistically compared between the SL and CDO groups with the aid of statistical software.b Hypothesis tests were 2-tailed, and values of P ≤ 0.05 were considered significant. Normality of data distribution was assessed by use of the D'Agostino-Pearson omnibus normality test. Numeric data were compared between groups with the unpaired t test (normally distributed data) or Mann-Whitney U test (nonnormally distributed data). Binary data were compared between groups with the χ2 or Fisher exact test. Unless otherwise indicated, normally distributed numeric data are reported as mean ± SD and nonnormally distributed numeric data are reported as median and range. Binary data are reported as a percentage of dogs in each group with various characteristics.
Results
Signalment
A total of 120 client-owned dogs were included in the study. The SL group (n = 62) consisted of 46 (74%) sexually intact females, 12 (19%) sexually intact males, 3 (5%) neutered males, and 1 (2%) spayed female. The CDO group (n = 58) consisted of 23 (40%) sexually intact females, 19 (33%) spayed females, 9 (16%) sexually intact males, and 7 (12%) neutered males. The SL group contained 12 (19%) Chihuahuas, 9 (15%) Pomeranians, 5 (8%) Dachshunds, 4 (6%) Alaskan Klee Kais, 4 (6%) mixed-breed dogs, 3 (5%) Yorkshire Terriers, 2 (3%) Australian Shepherds, 2 (3%) Japanese Chins, 2 (3%) Coton de Tulears, 2 (3%) Labrador Retrievers, 2 (3%) Maltese, and 1 (2%) each of various other breeds. The CDO group contained 6 (10%) Labrador Retrievers, 5 (8%) Border Collies, 5 (8%) German Shepherd Dogs, 4 (6%) Pembroke Welsh Corgis, 3 (5%) Newfoundlands, 3 (5%) mixed-breed dogs, 2 (3%) Miniature Australian Shepherds, 2 (3%) English Springer Spaniels, 2 (3%) Pomeranians, 2 (3%) Irish Setters, 2 (3%) American Staffordshire Terriers, and 1 (2%) each of various other breeds.
Preoperative data
Preoperative data for dogs in both groups were summarized (Table 1). Dogs in the CDO group were significantly older and heavier than dogs in the SL group. Six of the 62 (10%) dogs in the SL group had congenital cardiac defects diagnosed in addition to the PDA, including pulmonic stenosis (n = 3 [5%]), subaortic stenosis (2 [3%]), and aortic valve dysplasia (1 [2%]). One of the 58 (2%) dogs in the CDO group had subaortic stenosis. Echocardiographic data indicated that dogs in the CDO group had more pathological cardiac remodeling (as indicated by mitral regurgitation scores, LA:Ao, and fractional shortening values) than dogs in the SL group. Thoracic radiographs from the time of diagnosis were available for VHS calculation for 48 (77%) dogs in the SL group and 52 (90%) dogs in the CDO group, and these scores did not differ significantly between groups.
Summary of preoperative data for client-owned dogs with left-to-right shunting PDA treated by SL or CDO implantation.
| Variable | SL (n = 62) | CDO implantation (n = 58) | P value |
|---|---|---|---|
| Numeric data | |||
|   Age (mo) | 4 (2–78) | 8 (1.5–156) | < 0.001 |
|   Body weight (kg) | 2.8 (0.7–26.0) | 10.3 (2.7–38) | < 0.001 |
|   VHS* | 11.9 ± 1.1 | 12.4 ± 1.4 | 0.08 |
|   VIDdN | 2.046 ± 0.457 | 2.094 ± 0.455 | 0.56 |
|   LVIDsN | 1.310 (0.680–2.110) | 1.420 (0.850–2.640) | 0.08 |
|   LA:Ao* | 1.430 (0.970–3.740) | 1.575 (0.960–3.460) | 0.02 |
|   Fractional shortening (%) | 37 (10–56) | 33 (10–48) | < 0.001 |
|   Mitral regurgitation score | 1 (0–3) | 2 (0–4) | 0.009 |
| Categorical data | |||
|   Cardiac comorbidities | 6 (10) | 1 (2) | 0.11 |
|   Syncope | 2 (3) | 1 (2) | 1.00 |
|   Respiratory signs | 20 (32) | 16 (28) | 0.55 |
|   Left-sided CHF | 10 (16) | 16 (28) | 0.18 |
|   Arrhythmia | 8 (13) | 3 (5) | 0.20 |
|   Diuretics | 13 (21) | 14 (24) | 1.00 |
|   Inodilators | 2 (3) | 4 (7) | 0.71 |
|   ACE inhibitors | 6 (10) | 12 (21) | 0.21 |
Values for nonnormally distributed numeric data are reported as median (range), values for normally distributed numeric data are reported as mean ± SD, and values for categorical data are reported as number (%) of dogs with the indicated characteristic or treatment. Mitral regurgitation scores were assigned on a scale of 0 to 4 (none = 0, trace = 1, mild = 2, moderate = 3, and severe = 4). Values of P ≤ 0.05 were considered significant. To convert kilograms to pounds, multiply by 2.2.
Radiographs for VHS calculation were available for only 48 dogs in the SL group and 52 dogs in the CDO group.
ACE = Angiotensin-converting enzyme. CHF = Congestive heart failure.
Intraoperative data
Intraoperative data for dogs in both groups were summarized (Table 2). Durations of anesthesia and surgery were significantly longer in the CDO group than in the SL group. Dogs in the CDO group were more likely to have hypotension and to have received vasopressors, whereas dogs in the SL group were more likely to have received antiarrhythmic and parasympatholytic medications.
Summary of intraoperative data for the dogs in Table 1.
| Variable | SL (n = 62) | CDO implantation (n = 58) | P value |
|---|---|---|---|
| Numeric data | |||
|   Duration of surgery (min) | 95 (40–185) | 119.5 (45–240) | 0.003 |
|   Duration of anesthesia (min) | 144 (95–305) | 188.5 (103–360) | < 0.001 |
|   ASA status | 3 (2–4) | 3 (2–4) | 0.81 |
| Categorical data | |||
|   Hypotension | 25 (40) | 39 (67) | 0.003 |
|   Vasopressors | 23 (37) | 37 (64) | 0.005 |
|   Antiarrhythmics | 6 (10) | 1 (2) | 0.04 |
|   Parasympatholytics | 36 (58) | 19 (33) | 0.003 |
|   Major complications | 6 (10) | 0 (0) | 0.02 |
ASA = American Society of Anesthesiologists.
See Table 1 for remainder of key.
No major complications developed for any dog in the CDO group. However, for 6 (10%) dogs in the SL group, CDO had been first attempted on the same day as (n = 3), 1 day prior to (2), or 1 week prior to (1) the SL procedure but had failed. The attempted CDO procedure had been aborted in all instances because the femoral artery was judged too small to accommodate an appropriately sized introducer sheath, as determined by the attending board-certified veterinary cardiologist. Median duration of fluoroscopy for dogs in this group was 7.5 minutes (range, 3 to 26 minutes).
Six of the 62 (10%) dogs in the SL group developed major intraoperative complications. Three dogs had an inadvertent tear of the PDA, necessitating blood transfusion and leading to cardiopulmonary arrest. Two of these 3 dogs were successfully resuscitated. Their ductal tears were repaired with polydioxanone (3-0 suture for one dog and 5-0 suture for the other) in a simple continuous or interrupted pattern, followed by completed PDA dissection and ligation, and the dogs survived to discharge from the hospital 48 hours after surgery. Resuscitation was unsuccessful for the remaining dog, and a necropsy was subsequently performed by a board-certified veterinary cardiologist. The cause of death was deemed inadvertent ligation of the ascending aorta. A fourth dog in the SL group received an inadvertent lung laceration during chest tube placement that was successfully treated by partial lung lobectomy. A fifth dog in the SL group had minor intraoperative hemorrhage, and a modified Jackson-Henderson technique was consequently used to ligate the PDA; no residual ductal blood flow was observed after this surgery. The final dog in the SL group had no complications identified during surgery but had severe residual ductal flow 24 hours later. Revision surgery for this dog was successfully performed 5 months later by use of size-0 polypropylene suture; only data from the original surgery were included in the analyses.
Postoperative data
No significant differences were identified between groups in any evaluated postoperative variable except use of angiotensin-converting enzyme inhibitors (Table 3). Residual ductal blood flow the day after the procedure was characterized as trivial in 4 dogs in the SL group, mild in 4 dogs in the CDO group and 1 dog in the SL group, and severe in 1 dog in the SL group (the same dog that required revision surgery). All dogs survived to hospital discharge, except for the dog in the SL group that died during surgery (survival rates, 98% [61/62] for the SL group and 100% [58/58] for the CDO group).
Summary of postoperative data for the dogs in Table 1.
| Variable | SL (n = 62) | CDO implantation (n = 58) | P value |
|---|---|---|---|
| Residual ductal flow | 6 (10) | 4 (7) | 0.74 |
| Diuretics | 10 (16) | 15 (26) | 0.26 |
| Inodilators | 6 (10) | 11 (19) | 0.31 |
| ACE inhibitors | 6 (10) | 15 (26) | 0.02 |
| Survived to hospital discharge | 61 (98) | 58 (100) | 1.00 |
Values represent number (%) of dogs with the indicated characteristic or treatment.
See Table 1 for remainder of key.
Discussion
The primary objective of the present study was to directly compare major complications and rates of survival to hospital discharge between SL and CDO implantation for the treatment of left-to-right shunting PDA in dogs. Our findings suggested that successful outcomes may be expected with either procedure. The difference in major complication rates between the 2 procedures was significant, in agreement with our study hypothesis. Consistent with other findings in the extant peer-reviewed veterinary literature, the results of our study supported the supposition that PDA occlusion via SL or CDO implantation results in high rates of survival to hospital discharge, although the risk of major complications with SL must be considered when choosing a treatment method.
Dogs in the present study included a greater proportion of females than males in both groups (> 70% of dogs), similar to previous reports.1,10,13,21 Dogs in the SL group were also significantly younger and weighed less than those in the CDO group. This could be explained by size restrictions for the CDO group, whereby dogs considered too small for a CDO were routinely referred for SL at our institution. Additional reasons for referral for SL at our institution included the difference in cost between the 2 procedures and dogs having ductal diameters that exceed the maximum CDO size (ie, large-breed dogs). Breeds represented in the SL group were similar to those reported2 previously for dogs with PDA, generally consisting of toy or small breeds. Meanwhile, breeds in the CDO group were similar to those in a study22 involving PDA in older dogs, in which most (67%) were medium-sized to large-breed dogs.
Attempts at CDO deployment were performed and aborted in 6 dogs because of inadequate femoral artery diameter, and these failed attempts were followed by successful SL in all 6 dogs. The limiting factor in these dogs was not the size of the CDO device but rather the size of the requisite delivery sheath (5F or 7F, with an external diameter of approx 2 to 3 mm). The 6 dogs ranged in size from 2.7 to 4.4 kg (5.9 to 9.7 lb). At least one of these dogs had a ductal orifice measurement on transesophageal echocardiography that was larger than the measurement on preoperative transthoracic echocardiography, necessitating a larger delivery sheath than anticipated that subsequently failed to fit into the femoral artery. Given our data, we recommend against use of a threshold body weight as the sole factor when determining CDO candidacy and suggest that ductal size, ductal shape, body confirmation, and body condition (ie, presence and degree of obesity) also be considered. Our results are concordant with those of another study5 in which CDO was compared with other transvascular occlusion devices, indicating that the primary limitation of CDO implantation was dog size.
The preoperative data in the study reported here indicated that dogs in the CDO group had slightly more deleterious cardiac remodelling associated with the PDA than did dogs in the SL group. For example, LA:Ao and mitral regurgitation scores were higher in the CDO group, whereas fractional shortening was lower. Although differences between groups in other relevant variables such as LVIDdN, LVIDsN, VHS, and distributions of dogs with left-sided congestive heart failure were not significant, dogs in the CDO group appeared to have slightly more advanced disease. This pattern may be explained by the fact that dogs in the CDO group were significantly older, with a longer duration of shunting, than dogs in the SL group. Although the difference was not significant, concurrent cardiac defects were detected in 10% of dogs in the SL group and 2% of dogs in the CDO group. This was also consistent with the older nature of dogs in the CDO group, given that previous reports23,24 have suggested that up to 10% of young dogs with PDA may have concurrent defects, whereas such abnormalities are less prevalent in older dogs. Therefore, younger dogs with more abnormalities may have more clinical signs earlier and could be referred for intervention sooner than older dogs.
Durations of surgery and anesthesia were both significantly longer in the CDO group than in the SL group. Although no study has been reported regarding a direct comparison between SL and CDO implantation for the treatment of dogs with left-to-right shunting PDA, no difference in procedure duration was identified between SL and transarterial catheter coil occlusion in 1 study.11 Median duration of the CDO procedure was similar between our study and this other study11 (119.5 minutes vs 116 minutes, respectively); however, median duration of the SL procedure was briefer (95 minutes vs 107 minutes, respectively). In both studies, the duration of transesophageal echocardiography was included in the calculation of procedure duration for the CDO group (because this echocardiographic procedure was necessary to delineate ductal size and morphological characteristics) but not in the calculation for the comparison group. Duration of anesthesia in the other study11 was not reported, so no comparisons can be made between studies in this regard.
Both hypotension and the use of vasopressors were more common in the CDO group than in the SL group in the present study, and this could have been related to the longer duration of anesthesia in the CDO group. Meanwhile, intraoperative use of antiarrhythmic and parasympatholytic drugs was more prevalent in the SL group, possibly because of arrhythmias caused by manual handling of the heart. Arrhythmias were less common in the CDO group, likely because of the manipulation of catheters occurring primarily in the great vessels with the CDO deployment.
The difference in major intraoperative complication rates between the SL and CDO groups (10% vs 0%, respectively) was significant (P = 0.02) in the study reported here. The rate of intraoperative hemorrhage during the SL procedure (6%) was comparable to that in previous studies1,7,12,13 (1% to 17%). In other studies7,10,11,13 of SL for PDA occlusion in dogs, mortality rates ranged from 0% to 7%, similar to the 2% mortality rate for this procedure in the present study. The only death in our study resulted from severe hemorrhage from a ductal tear causing poor visibility and accidental ligation of the aorta. Mortality rates approaching 0% are possible when surgeons are experienced.10 Size of PDA may play a role in complications, and the larger size of the ductus arteriosus in older versus younger dogs may be associated with a higher risk of bleeding during surgery.1,6,7 Aside from hemorrhage, the other 2 major complications in the present study were related to technical errors during surgery (inadvertent lung laceration during chest tube insertion and failure to tighten the PDA ligature adequately during the first surgery).
The Jackson-Henderson technique was used in only 1 dog in the present study owing to ductal hemorrhage. This dog did not require a blood transfusion and survived to discharge with no residual ductal blood flow noted. In a previous study,21 standard ligation and the Jackson-Henderson technique for PDA occlusion were compared, revealing more residual flow with the Jackson-Henderson technique. Given that only 1 dog was treated with this technique in the present study, no comparisons can be made with this other study.
In another study11 in which SL was compared with transarterial coil placement for PDA occlusion in dogs, the success rate (defined as survival to hospital discharge without requiring a second procedure) was 94% for SL and 84% for coil occlusion. If this definition of success were applied to the present study, the success rates would have been 97% (60/62) and 100% (58/58) for the SL group and the CDO group, respectively. The CDO procedure was more successful (98% to 100%) than the coil procedure (86%) for PDA occlusion in a previous study.5 In that study, the mean percentage of residual ductal blood flow in the CDO group was 3%, which was significantly lower than that in the coil occlusion group (45%). The high success rates achieved with both SL and CDO implantation in the present study suggested that these techniques are superior to coil occlusion.5,11
The main limitation of the present study was its retrospective nature and the lack of long-term outcome assessment; however, long-term outcomes for dogs treated for PDAs that survive to hospital discharge are reportedly excellent.10,16,17 Reported survival times following ductal occlusion range from 11 to 14 years.17,25 A large retrospective study16 involving 520 dogs treated for PDA showed that long-term reverse remodeling (ie, smaller cardiac chamber volumes) occurred in most treated dogs. In addition, all dogs that received a CDO device in the present study were treated via a femoral arteriotomy approach, and a transvenous approach may have permitted CDO implantation by accommodating a relatively large delivery sheath.26 A final factor for consideration is that the study was performed at a teaching institution, where resident training could influence complication rates, as suggested previously,13 as well as durations of anesthesia and surgery.
The present study yielded important comparative information about complications and rates of survival to hospital discharge associated with the 2 most current treatment approaches for PDA in dogs. Given the results, we concluded that SL and CDO implantation were both viable treatment methods for left-to-right shunting PDAs with comparably high rates of survival to hospital discharge. The higher intraoperative complication rate associated with SL and the limitations of CDO device sizing should be considered when choosing a treatment method for a dog with PDA.
ABBREVIATIONS
| CDO | Canine ductal occluder |
| LA:Ao | Left atrial-to-aortic root diameter ratio |
| LVIDd | Left ventricular internal diameter during diastole |
| LVIDdN | Left ventricular internal diameter during diastole, normalized to body weight |
| LVIDs | Left ventricular internal diameter during systole |
| LVIDsN | Left ventricular internal diameter during systole, normalized to body weight |
| PDA | Patent ductus arteriosus |
| SL | Surgical ligation |
| VHS | Vertebral heart scale |
Footnotes
Amplatz CDO, Infiniti Medical LLC, Menlo Park, Calif.
GraphPad Prism, version 6.02, GraphPad Software Inc, San Diego, Calif.
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