Structural and functional cardiovascular changes and their consequences following interventional patent ductus arteriosus occlusion in dogs: 24 cases (2000–2006)

Christopher D. Stauthammer Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.

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Anthony H. Tobias Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.

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Damon B. Leeder Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.

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Maxie U. Krüger Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.

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Abstract

Objective—To investigate cardiovascular changes and survival times following complete interventional device occlusion of uncomplicated left-to-right shunting patent ductus arteriosus in dogs.

Design—Retrospective cohort study.

Animals—24 dogs with uncomplicated patent ductus arteriosus that was fully occluded and reevaluated within 24 hours, approximately 3 months, and 1 year after the procedure.

Procedures—Information on medical history, diagnostic imaging findings, treatment received, and survival times were obtained from medical records. Patients were allocated into 2 groups on the basis of age (< 1 year [n = 14] and ≥ 1 year [10]) at the time of the procedure. Additional follow-up information was obtained through interviews of owners and referral veterinarians.

Results—Following ductal occlusion, decreases were detected in vertebral heart scale size, left ventricular chamber diameter in diastole and in systole, left atrial dimension, fractional shortening, aortic velocity, and ventricular wall thickness. There were no differences between age groups for postocclusion changes except vertebral heart scale size. Systolic dysfunction was detected in 14 (58%) patients on the final visit. Median survival time for all dogs after ductal occlusion was > 11.5 years.

Conclusions and Clinical Relevance—Complete ductal occlusion resulted in immediate removal of the volume overload state and eventual return of cardiac chamber dimensions to reference range, suggesting regression of eccentric hypertrophy. Systolic dysfunction persisted in some dogs but appeared to be clinically unimportant. Most cardiovascular changes were independent of patient age at the time of the procedure.

Abstract

Objective—To investigate cardiovascular changes and survival times following complete interventional device occlusion of uncomplicated left-to-right shunting patent ductus arteriosus in dogs.

Design—Retrospective cohort study.

Animals—24 dogs with uncomplicated patent ductus arteriosus that was fully occluded and reevaluated within 24 hours, approximately 3 months, and 1 year after the procedure.

Procedures—Information on medical history, diagnostic imaging findings, treatment received, and survival times were obtained from medical records. Patients were allocated into 2 groups on the basis of age (< 1 year [n = 14] and ≥ 1 year [10]) at the time of the procedure. Additional follow-up information was obtained through interviews of owners and referral veterinarians.

Results—Following ductal occlusion, decreases were detected in vertebral heart scale size, left ventricular chamber diameter in diastole and in systole, left atrial dimension, fractional shortening, aortic velocity, and ventricular wall thickness. There were no differences between age groups for postocclusion changes except vertebral heart scale size. Systolic dysfunction was detected in 14 (58%) patients on the final visit. Median survival time for all dogs after ductal occlusion was > 11.5 years.

Conclusions and Clinical Relevance—Complete ductal occlusion resulted in immediate removal of the volume overload state and eventual return of cardiac chamber dimensions to reference range, suggesting regression of eccentric hypertrophy. Systolic dysfunction persisted in some dogs but appeared to be clinically unimportant. Most cardiovascular changes were independent of patient age at the time of the procedure.

Patent ductus arteriosus is a common congenital cardiovascular disorder in dogs that results in volume overload and eccentric hypertrophy of the left side of the heart.1 Left ventricular systolic dysfunction may also develop secondary to the volume overload state.2–4 Ductal closure is considered curative.3,5,6 However, little is known about postclosure cardiovascular changes. It is presumed that chamber dimensions and myocardial mass return to reference range following ductal closure.7 Reductions in left ventricular and atrial chamber dimensions have been reported as well as return of left ventricular systolic function to reference range in selected patients.3,8–10,a However, evidence to indicate return of cardiac size and function to reference range following PDA closure is limited and confounded by the inclusion of patients with residual ductal flow, congestive heart failure, or concurrent cardiac disease. Consequently, the objective of the study reported here was to investigate the cardiac changes that occurred following complete occlusion of uncomplicated left-to-right shunting PDA in dogs. We hypothesized that removal of the left-sided volume overload would result in reversal of eccentric hypertrophy, with return of left heart chamber dimensions and left ventricular systolic function to reference ranges.

Materials and Methods

Case selection—Medical records of all dogs with PDA at the University of Minnesota Veterinary Medical Center between 2000 and 2006 were reviewed. Dogs were included if an uncomplicated left-to-right shunting PDA was confirmed by use of physical examination, thoracic radiography, ECG, echocardiography, and angiography and if the PDA was fully occluded as determined by use of color flow Doppler echocardiography performed 24 hours, approximately 3 months, and 12 months after the procedure. The term uncomplicated was defined as left ventricular FS > 23% and absence of congestive heart failure, concurrent congenital or acquired heart disease, atrial fibrillation, and ventricular arrhythmias.

For inclusion, dogs needed to have undergone full evaluations at 4 defined time points: before occlusion and 24 hours, approximately 3 months, and ≥ 12 months after occlusion. A full evaluation included physical examination, thoracic radiography, and echocardiography. Electrocardiography was performed in most cases at each evaluation, but this was not required for inclusion. Congestive heart failure was defined as the concurrent presence of clinical respiratory tract signs and pulmonary infiltrates on thoracic radiography or the presence of ascites with hepatic venous distention. Dogs receiving diuretics or positive inotropic medications upon initial evaluation were excluded. Patients with mitral regurgitation were included if there was no evidence on echocardiography of myxomatous degeneration, valve dysplasia, or other morphological alterations in the mitral valve apparatus. Neither the severity of mitral regurgitation nor direction of the regurgitant jet was used as an exclusion criterion. Dogs undergoing surgical ligation of the PDA were not considered for this study because of the difficulty in performing an echocardiogram within 24 hours after the ligation procedure.

Medical records review—Medical records were reviewed regarding diagnostic procedures and their results, treatments and their results, and outcome. Six-lead ECG was performed with the patient in right lateral recumbency, and R wave amplitude in lead II was measured. The patient's rhythm was monitored for a minimum of 5 minutes. Vertebral heart scale size was measured from right lateral thoracic radiographic views.11

Transthoracic echocardiography was performed with dogs in lateral recumbency. M-mode, 2-D, and Doppler studies were performed by or under the direct supervision of a board-certified cardiologist (AHT) in accordance with the recommendations of the American Society of Echocardiography.12 The ductus arteriosus was visualized from both the right parasternal short-axis and left cranial parasternal views. Doppler echocardiography was used to confirm left-to-right shunting through the ductus arteriosus on the initial evaluation and absence of residual flow after occlusion. Aortic velocities were recorded from the left parasternal view. Left ventricular diameter in diastole and systole, LAD, and IVSd and LVPWd were measured from 2-D-guided M-mode images recorded from the transverse imaging planes. A minimum of 3 measurements was recorded for each variable, and mean values were calculated. M-mode measurements were indexed by allometric scaling on the basis of body weight at each visit, as described by Cornell et al.13 Reference values13 were used for indexed M-mode measurements. M-mode measurements were used to calculate left ventricular FS.

Indices of left ventricular systolic function included FS and indexed LVDs. Systolic dysfunction was defined as FS < 23% or indexed LVDs > 1.26.13 Patients were considered to have systolic dysfunction if one of these indices was outside of the reference range.

During September 2011, referring veterinarians and owners were interviewed by telephone to obtain long-term follow-up information. Questions included whether the dog was alive, cause of death for deceased dogs, whether the dog had developed any clinical signs of cardiovascular disease, and whether the dog had or was receiving any cardiovascular medications.

Statistical analysis—Descriptive data are presented as median (range) values. Repeated-measures models were constructed to compare main effects of measurement over time and age category at occlusion as well as interaction between time and age category. A variance components covariance structure was assumed between residuals of the same subject (dog) in the model. Post hoc comparisons were performed by use of the Tukey correction for multiple comparisons. Survival analysis was performed by use of the Kaplan-Meier method with the primary endpoint defined as all causes of death and a secondary endpoint of death from cardiovascular causes. Statistical analyses were performed with commercially available software.b,c For all comparisons, values of P < 0.05 were considered significant.

Results

Thirty-one dogs underwent interventional PDA occlusion during the study period. All occlusion procedures were performed with a catheter and a variety of nitinol devices.10,14,d Seven dogs were excluded because of the presence of atrial fibrillation at initial evaluation (n = 1), residual flow through the occlusive device (2), sepsis from device infection (1), concurrent subaortic stenosis (1), or lack of follow-up information (2). No dogs that met the inclusion criteria on the initial visit died, developed congestive heart failure, or had an arrhythmia during subsequent visits. The study population consisted of 24 dogs (18 females and 6 males). Age and weight at the preocclusion evaluation were 0.94 years (range, 0.33 to 4.93 years) and 9.45 kg (20.79 lb; range, 3.70 to 31.10 kg [8.14 to 68.42 lb]), respectively. Twenty breeds were represented, including Shetland Sheepdog (n = 2), Maltese (1), mixed (1), Collie (2), Border Collie (1), German Shepherd Dog (1), Yorkshire Terrier (1), Miniature Schnauzer (1), Irish Setter (2), Coton de Tulear (1), Pembroke Welsh Corgi (1), Newfoundland (1), Miniature Poodle (2), Bichon Frise (1), English Springer Spaniel (2), Pomeranian (1), Jack Russell Terrier (1), Fox Terrier (1), and Greyhound (1). Dogs were examined 1 day (1 to 112 days) prior to ductal occlusion, and 1 day (termed the 24-hour evaluation), 100 days (78 to 191 days [termed the 3-month evaluation]), and 404 days (348 to 1,290 days [termed the 12-month evaluation]) after occlusion. Fourteen dogs were < 1 year of age, and 10 dogs were ≥ 1 year of age at the time of ductal occlusion.

Preocclusion data revealed increased R wave amplitude, VHS size, LVDd, LVDs, and LAD (Table 1). Diastolic wall thickness measurements were within reference range. Following ductal occlusion, R wave amplitude was decreased at the 3-month evaluation and had returned to reference range at the 12-month evaluation. Indexed LVDd was decreased immediately after ductal occlusion and again at the 3-month evaluation, at which time values were within reference range. Indexed LAD was decreased at each visit and returned to reference range by the 3-month evaluation. The LVPWd was increased immediately following occlusion but remained within reference range, and had returned to baseline at the 3-month evaluation. A decrease in IVSd occurred between the 24-hour evaluation and the 12-month evaluation. Peak aortic outflow velocity was decreased immediately following occlusion and again at the 24-hour evaluation and the 3-month evaluation.

Table 1—

Least squares mean ± SE values of echocardiographic variables and R wave amplitude before and at various intervals after interventional PDA occlusion in 24 dogs.

VariableBefore24 hours after3 months after> 12 months afterReference rangeP value
IVSd (cm)0.44 ± 0.020.46 ± 0.020.42 ± 0.020.41 ± 0.020.29–0.590.033
LVDd (cm)2.12 ± 0.051.88 ± 0.051.82 ± 0.051.64 ± 0.051.27–1.85< 0.001
LVPWd (cm)0.41 ± 0.010.47 ± 0.010.42 ± 0.010.41 ± 0.010.29–0.60< 0.001
LVDs (cm)1.36 ± 0.041.34 ± 0.041.32 ± 0.041.17 ± 0.040.71–1.26< 0.001
LAD (cm)1.11 ± 0.030.99 ± 0.030.88 ± 0.030.78 ± 0.030.59–0.97< 0.001
FS (%)33 ± 125 ± 124 ± 124 ± 123–47< 0.001
Aortic velocity (m/s)2.03 ± 0.091.28 ± 0.101.01 ± 0.091.08 ± 0.09< 2.2< 0.001
R wave amplitude (mV)4.1 ± 0.24.4 ± 0.33.3 ± 0.32.8 ± 0.3< 3.0< 0.001
VHS size (vertebral bodies)11.7 ± 0.1411.2 ± 0.1410.8 ± 0.1410.7 ± 0.14< 10.7< 0.001

P value relates to the overall main effect of time on each variable.

Preocclusion LVDs was greater than reference range and remained so at the 24-hour and the 3-month evaluations; however, it decreased into the upper portion of the reference range at the 12-month evaluation. Left ventricular FS decreased immediately after occlusion and did not change significantly during the remainder of the study.

There was no main effect of age at occlusion on any cardiac variable, with the exception of VHS size, which decreased during the study period but was consistently slightly smaller in dogs that had their PDAs occluded at < 1 year of age.

Fourteen (58%) dogs had evidence of systolic dysfunction at the 12-month evaluation. Six (25%) dogs had abnormalities in both variables of systolic function, whereas 8 (33%) dogs had abnormalities in 1 variable. The FS was abnormal in 13 (54%) dogs, whereas LVDs was abnormal in 7 (29%) dogs.

Survival analysis revealed a median survival time of > 11.5 years after ductal occlusion for dogs that died from any cause (no dogs died from cardiovascular causes; Figure 1). No dog developed congestive heart failure or arrhythmia during the follow-up period. None received any cardiac medications or reached the endpoint of cardiovascular-related death or euthanasia. Three dogs were euthanized for non-cardiovascular-related causes (aggression [n = 1] and orthopedic disease [2]).

Figure 1—
Figure 1—

Kaplan-Meier survival curves for 24 dogs following interventional PDA occlusion. The gray line represents cardiovascular deaths. The black line represents all causes of death.

Citation: Journal of the American Veterinary Medical Association 242, 12; 10.2460/javma.242.12.1722

Discussion

In the present study population of dogs with uncomplicated PDA, complete occlusion resulted in immediate removal of the left-sided volume overload with subsequent return of left heart chamber dimensions and wall thickness to reference ranges. With the exception of VHS size, all postocclusion cardiac changes were independent of age category at the time of the procedure. Generally, systolic function among the 24 study dogs improved. However, 58% of dogs had some evidence of systolic dysfunction at the 12-month evaluation. Despite this, and the fact that no dogs received any cardiovascular medications, median congestive heart failure-free survival time after occlusion was > 11.5 years, confirming that complete occlusion of uncomplicated PDA in these dogs was curative.

The presence of eccentric hypertrophy has been well described in dogs with left-to-right shunting PDAs and is characterized by left-sided chamber dilation with normal wall thickness and increased myocardial mass.2–4,15,16 In the present study, the baseline data also reflected the presence of eccentric hypertrophy with increased left-sided chamber dimensions and normal wall thickness.

Ductal occlusion quickly removes the left-sided volume overload because blood is no longer shunting from the aorta and returning to the left side of the heart via the pulmonary circulation. Removal of the volume overload state abruptly decreases left-sided chamber dimensions and aortic velocities.9,10,17 Data from the present study, including significant decreases in LVDd, LAD, and aortic peak velocity, were consistent with the literature. However, eccentric hypertrophy persisted immediately after occlusion as indicated by the failure of LVDd and LAD to return to reference range and increased LVPWd thickness.

Given that left ventricular eccentric hypertrophy occurs secondary to the presence of a volume overload state, it is conceivable that regression of hypertrophy (reverse remodeling) characterized by reduction in myocardial mass and cardiac chamber dimensions would occur following PDA occlusion. Our data indicated regression of eccentric hypertrophy following complete occlusion of uncomplicated PDAs. Long-term reductions were observed in VHS size and R wave amplitude with continual reduction and return to reference range in left-sided cardiac chamber dimensions (LAD and LVDd), compared with the results obtained immediately following ductal occlusion (at the 24-hour evaluation). Wall thickness also decreased from the immediate postocclusion state, returning to the preocclusion values, which suggested a reduction in myocardial mass. Given the reduction in wall thickness, the chronic changes in cardiac dimensions were unlikely to be the result of progressive reductions in volume load but instead caused by reverse remodeling.

Reverse remodeling has recently been reported in human patients after PDA closure with progressive reduction of left ventricular end diastolic volume indices 6 months after closure, compared with indices acquired immediately (24 hours to 1 week) after the procedure.18,19 Reverse remodeling has also been suggested to occur following PDA occlusion in dogs. Long-term reductions in radiographic cardiac silhouette size and R wave amplitude on ECG have been noted following ductal ligation.20,21 Van Israel et al8 found reductions in left ventricular chamber dimensions during an extended period following ductal ligation but could not distinguish between reductions in chamber size secondary to removal of the volume overload state versus regression of eccentric hypertrophy because they did not evaluate dogs immediately after the procedure. Campbell et al9 detected a progressive reduction in indexed LVDd during an extended follow-up period ranging from 12 to 63 months following PDA occlusion, suggesting reverse remodeling. However, many of their study dogs did not have return of indexed LVDd or left atrial size to reference ranges, possibly because of residual ductal flow in 12 of their 31 cases.

Immediately after occlusion of the ductus arteriosus, a decrease was detected in FS with no change in LVDs. This finding has been reported and speculated to be a result of the combination of decreased left ventricular preload and increased afterload secondary to PDA occlusion.1–3,8,22 Similar changes are noted in humans immediately after ductal occlusion.18,19,23 Over the long term in the present study population, indexed LVDs decreased without further change in FS. Mean indexed LVDs returned to reference range by the 12-month evaluation, indicating improvement in systolic function. However, this did not occur in all dogs and during the final visit, 14 (58%) dogs met the criterion of systolic dysfunction in that 1 or more variables were abnormal. Thus, our hypothesis that complete ductal occlusion would result in return to normal LV systolic function was only partially correct.

The reported frequency of residual systolic dysfunction in dogs after ductal occlusion ranges from 23% to 54%.8,24,a No predictors of postprocedural systolic function have been identified. We had suspected that the inclusion of dogs with sequelae of PDA, residual shunting, or concurrent cardiac disease would increase the prevalence of systolic dysfunction. However, the results clearly indicated that systolic dysfunction persisted in many uncomplicated cases as well. Conflicting reports have been published in regard to systolic function in human patients after PDA occlusion. Return to normal systolic function has been documented within 6 months after the procedure in a prospective study19 involving 37 children < 11 years of age and in a single case report25 involving a septuagenarian. However, a longitudinal study18 involving 45 adults > 18 years of age at the time of the procedure found 11% of patients with persistent LV systolic dysfunction at long-term follow-up (6 to 45 months). The authors reported that for the entire population, EF recovered, compared with findings immediately after closure (within 1 week); however, EF remained low, compared with findings before the procedure. The authors identified preclosure EF as the only independent predictor of late normal postclosure EF within reference range.

Despite 58% of the dogs in the present study having systolic dysfunction, median survival time for all dogs was > 11.5 years after ductal occlusion. No cardiac-related deaths were reported, and no dog received cardiac medications. The data confirm that the presence of systolic dysfunction after ductal occlusion is clinically unimportant, because affected dogs had excellent outcomes, as has been reported.2,3,24

Patient age category (< 1 year or ≥ 1 year) at the time of ductal occlusion was not associated with the cardiovascular changes in our study population except for VHS size. This finding was in contrast with a previous report24 that echocardiographic changes are rarely reversible in older dogs. This difference may have resulted from inclusion of patients with residual flow, heart failure, or concurrent cardiac disease. However, previous studies7,8 have found that patient age at the time of ductal closure was not associated with a difference in survival time. In 1 study, Van Israel et al8 found no difference in survival times among any of the subgroups, which varied in age from 0 to 6 months to > 24 months of age at the time of ductal closure.

The present study had certain limitations. The patient population comprised uncomplicated cases as defined by the absence of congestive heart failure, arrhythmia, or concurrent cardiac disease. In addition, this definition included a normal FS on the preductal occlusion evaluation. Results of the study should be extrapolated with utmost caution to dogs with PDA that fail to meet the same criteria.

A major limitation was the lack of evaluation of myocardial mass. Eccentric hypertrophy results in an overall increase in myocardial mass with chamber dilation.26 Definitive regression of eccentric hypertrophy would be characterized by a return of chamber diameters and wall thickness to reference ranges with a reduction in myocardial mass. Various echocardiographic methods for calculation of myocardial mass have been described, including the Teichholz formula, modified Simpson's disk method, and the length-area formula. The authors contemplated use of the Teichholz formula for evaluation of myocardial mass. However, this formula overestimates left ventricular volume and potentially mass.27,28 Given the retrospective nature of the present study, the described 2-D methods of mass and volume calculation could not be used.

Another limitation was in use of FS as a parameter of systolic function. The FS is merely the percentage change in left ventricular chamber dimensions between diastole and systole.15 The FS is highly load dependent because it is influenced by changes in ventricular preload, afterload, and contractility. Such variables are not only affected by shunt occlusion but also by changes in heart rate, hydration status, and blood pressure, which could not be taken into account. In addition, the M-mode variables used to calculate FS are recorded from the transverse plane of the left ventricle and only assess circumferential movement of the ventricular walls. The FS does not account for contraction along the long axis of the left ventricle or apicobasilar movement. The failure of FS to return to reference range in all of the study dogs may have been influenced by a greater effect on apicobasilar versus circumferential contraction with regression of eccentric hypertrophy. A more global assessment of left ventricular systolic function would have been provided through calculation of ventricular volume and EF, the percentage change in left ventricular volume. As stated with regard to myocardial mass assessment, such calculations could not have been determined given the retrospective nature of the study.

Complete occlusion of the ductus arteriosus in uncomplicated cases in dogs resulted in the immediate removal of the volume overload state with longer term regression of eccentric hypertrophy. Systolic dysfunction may persist after ductal occlusion, but this is not clinically consequential and requires no treatment. The cardiovascular changes that occurred after ductal occlusion, with the exception of VHS size, were independent of patient age at the time of the procedure.

ABBREVIATIONS

EF

Ejection fraction

FS

Fractional shortening

IVSd

Interventricular septal thickness in diastole

LAD

Left atrial dimension

LVDd

Left ventricular chamber diameter in diastole

LVDs

Left ventricular chamber diameter in systole

LVPWd

Left ventricular posterior wall thickness in diastole

PDA

Patent ductus arteriosus

VHS

Vertebral heart scale

a.

Oliveira P, Domenech O, Silva J, et al. Percutaneous closure of patent ductus arteriosus with Amplatz Canine Duct Occluder in 46 dogs: outcome and prognostic survival factors (abstr), in Proceedings. 19th Eur Coll Vet Intern Med Companion Anim 2009;217.

b.

SAS, version 9.2, SAS Institute Inc, Cary, NC.

c.

NCSS 2007, NCSS, Kaysville, Utah.

d.

Tobias AH, Jacob KA, Fine DM, et al. Patent ductus arteriosus occlusion with Amplatzer duct occluders (abstr), in Proceedings. 20th Annu Am Coll Vet Intern Med Forum 2002;100–101.

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