Use of combined cutting balloon and high-pressure balloon technique for the treatment of double-chambered right ventricle or primary infundibular stenosis: a case series.

Five dogs and two cats with a diagnosis of double-chambered right ventricle or primary infundibular stenosis were referred to undergo a combined cutting balloon and high-pressure balloon technique. At admission five cases were asymptomatic, one had a history of syncope and one had signs of right-sided congestive heart failure. Each patient underwent a complete transthoracic echocardiogram, thoracic radiographs, an angiogram and the combined interventional procedure. Median diameter of the right mid-ventricular stenosis was 4 mm (range 2-8.7 mm) in dogs, and it measured 1.9 and 2 mm in cats. Under general anesthesia initial dilation with an 8-mm × 2-cm cutting balloon was performed from a left external jugular vein approach followed by dilation with a high-pressure balloon (1.5:1 balloon diameter-right outflow tract diameter ratio). In one dog and the two cats the procedure was not completed due to technical issues. In the other four dogs the median intracavitary proximal chamber pressure decreased from 100 mmHg (range 70-150 mmHg) before the procedure to 57 mmHg (range 45-70 mmHg) post-dilation. Long-term follow-up (from six months to two years) showed complete or partial reverse remodeling of the proximal chamber with a median residual pressure gradient below 80 mmHg (range 46-75 mmHg) for all four dogs. This case series shows that this procedure should be considered in dogs with right ventricular outflow tract obstruction. In cats, the procedure might be feasible, if additional guidewire inventory were available.

The next heartbeat: Creating dynamic and histographic Poincaré plots for the assessment of cardiac rhythms.

The rhythm of the heart is not a stationary phenomenon, and therefore, incorporation of the dynamic Poincaré plot and tachogram provides additional diagnostic information to complement and expand waveform (P-QRST) analyses from the electrocardiogram. Although pattern assessment of the Poincaré plot and tachogram can provide an appraisal for normal and abnormal rhythms and serve as a potential means for machine-learned rhythm diagnoses, time-selected windows of beat-to-beat variability permit more detailed examination. As such, expanded criteria for rhythm diagnoses, identification of arrhythmic triggers, global appreciation of rhythm changes, and recognition of patterns that provoke mechanistic questions may be gleaned from the use of the methods reviewed in this report. More specifically, these methods demonstrate that limitations exist in the reliance on traditional measures of heart rate variability in the dog due to the non-linear beat-to-beat rhythm of sinus arrhythmia in the species. Behavior of arrhythmias based on coupling intervals, repeating patterns, preceding triggers of beat-to-beat variability, and circumstantial evidence of atrioventricular nodal conduction during atrial flutter and fibrillation are a few examples of discovery founded in these techniques. The open access website, The Next Heartbeat (https://thenextheartbeat.com/), permits anyone to implement these methods in the assessment of long-term electrocardiographic examinations (Holter monitoring) so that, as yet to be revealed, features of the beating heart through time may be discovered.

Two-dimensional echocardiographic estimates of left ventricular volumes obtained in different views in dogs provide similar measurements but are not interchangeable.

INTRODUCTION: Little information exists regarding the interchangeability of left ventricular volume estimates using a monoplane Simpson's Method of Discs on images obtained from the left apical four-chamber and right parasternal long axis four-chamber views. We examined if volume estimates obtained from these views were interchangeable. ANIMALS: A total of 224 dogs: 86 healthy, 96 with mitral valve disease, 42 with various cardiac pathologies. MATERIALS AND METHODS: Investigators obtained right parasternal long-axis and left apical four-chamber views from each dog and used manufacturer-supplied software to estimate left ventricular volumes in diastole and systole using Simpson's Method of Discs. Estimates based on linear measurements (diameter cubed, 0.67∗diameter cubed, and Teichholz) were also calculated. Reproducibility for each view, and agreement between the estimates obtained with each view, and those calculated from linear dimensions, were examined using Limits of Agreement. Reference intervals for volumes indexed to bodyweight and body surface area were calculated. RESULTS: Neither method proved very reproducible. Although no bias was detected, the agreement between volumes indexed to bodyweight and body surface area was insufficient to recommend interchangeability. Estimates based on Teichholz and diameter cubed methods overestimated volumes; however, those based on 0.67∗diameter cubed performed reasonably. CONCLUSIONS: Monoplane volume estimates from the left apical and right parasternal long axis four-chamber views are similar but not interchangeable. Clinicians can perform crude estimates of left ventricular volume using the equation 0.67∗diameter cubed.

Low-energy ablation of anteroseptal accessory pathways in two dogs.

In humans, accessory pathways (APs) in an anteroseptal and midseptal position are often challenging to ablate because of their close proximity with the conduction pathways of the atrioventricular junction. The use of low-energy ablation techniques can be useful to reduce the risk of permanently damaging the atrioventricular node and the His bundle. This report describes the use of low-energy radiofrequency catheter ablation to successfully and permanently ablate anteroseptal APs in two dogs with orthodromic atrioventricular reciprocating tachycardia. In the first dog, a transient first degree atrioventricular block persisted for 30 s after radiofrequency energy delivery. In the second dog, transient paroxysmal atrioventricular conduction block was observed during the procedure but resolved within 3 days. First degree atrioventricular block was again identified 2 months later. In conclusion, anteroseptal APs can be effectively treated by low-energy radiofrequency catheter ablation with minimal and transient damage to the atrioventricular junction.

Tricuspid annular plane systolic excursion-to-aortic ratio provides a bodyweight-independent measure of right ventricular systolic function in dogs.

OBJECTIVES: To evaluate whether tricuspid annular plane systolic excursion (TAPSE) can be normalized to aortic valve (Ao) measurements in dogs. To determine TAPSE:Ao reference intervals for healthy dogs and examine diagnostic performance of TAPSE:Ao in dogs with pulmonary hypertension (PH). ANIMALS: One hundred and thirty-seven healthy adult dogs; 115 dogs with myxomatous mitral valve disease (MMVD) but no PH; 91 dogs with PH. METHODS: A combined prospective and retrospective study. Full echocardiographic evaluations were performed on all dogs; TAPSE was indexed to Ao to produce a unitless TAPSE:Ao. Reference intervals for TAPSE:Ao were generated, and TAPSE:Ao was regressed on tricuspid regurgitant jet velocity in dogs with PH and on LA:Ao in dogs with MMVD without PH. Diagnostic test analysis was used to examine the ability of TAPSE:Ao to identify severe PH. An adjusted TAPSE:Ao (TAPSE:Ao(adj)) was derived to account for MMVD in dogs with PH. RESULTS: The ratio, TAPSE:Ao, removed the effect of bodyweight from TAPSE measurements. Healthy dogs had TAPSE:Ao > 0.65. The ratio, TAPSE:Ao, showed a linear negative relationship with tricuspid regurgitation velocity and positive relationship with LA:Ao. The adjusted ratio, TAPSE:Ao(adj), increased the sensitivity of diagnosis of PH in dogs with moderate-severe MMVD without affecting the diagnosis of PH in dogs with PH and with no or mild MMVD. CONCLUSIONS: The ratios, TAPSE:Ao and TAPSE:Ao(adj), are a bodyweight-independent means of assessing right ventricular systolic function in dogs and for identifying severe PH in dogs with or without MMVD.

Structural and molecular pathology of the atrium in boxer arrhythmogenic right ventricular cardiomyopathy.

OBJECTIVE: To investigate the expression and distribution of desmosomal and gap junction proteins of the intercalated disc in the atria of boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC). ANIMALS: Nineteen control dogs and 13 boxers with histopathologically confirmed ARVC. METHODS: Right and left atrial samples were examined using immunofluorescence and Western blots. The intercalated disc proteins investigated included total and phosphorylated connexin43 (Cx43 and pCx43), connexin45, connexin40, plakoglobin, plakophilin-2, desmoplakin, and N-cadherin. RESULTS: Histopathological changes characteristic of ARVC were present in the left or right atrium of 12 out of 13 boxers and were absent in all control dogs. When compared to the 19 control dogs, immunofluorescence analysis revealed a decrease in signal intensity for pCx43 and plakoglobin in the left (p = 0.03 and p = 0.014, respectively) and right atrium (p = 0.015 and p = 0.002, respectively) of affected boxers. Connexin43 and pCx43 Western blot band density was significantly decreased in the left (p = 0.025 and p = 0.027, respectively) and right atrium (p = 0.001 and p = 0.044, respectively) of affected boxers. CONCLUSION: Altered intercalated disc and gap junction proteins were identified in atrial myocardium of ARVC boxers, supporting atrial involvement as part of this disorder. Reduction in pCx43 in conjunction with histological changes could represent the substrate for atrial arrhythmias associated with ARVC. Furthermore, these findings detected in boxer dogs, lend support for the broader term, arrhythmogenic cardiomyopathy, as preferred nomenclature used to describe this disease in humans.

Tricuspid annular plane systolic excursion (TAPSE) in dogs: reference values and impact of pulmonary hypertension.

BACKGROUND: The impact of pulmonary hypertension (PH) on right ventricular systolic function is difficult to assess. Tricuspid annular plane systolic excursion (TAPSE) is an echocardiographic measurement of right ventricular systolic function and a strong predictor of outcome in human PH patients. HYPOTHESIS/OBJECTIVES: Determine a reference range for TAPSE in healthy dogs, and quantify TAPSE in dogs with PH. It is hypothesized that TAPSE is lower in dogs with PH compared with a reference group, and decreases as PH worsens. ANIMALS: Fifty normal dogs and 30 dogs with PH. METHODS: TAPSE was measured by 2-dimensional echocardiography-guided M-mode from the left apical 4-chamber view. Peak systolic tricuspid valve regurgitation jet velocity was measured by continuous-wave Doppler to estimate right ventricular-to-right atrial pressure gradient. PH was subjectively classified as mild, moderate, and severe. RESULTS: There was a curvilinear correlation between TAPSE and body weight. The upper and lower limits of the 95% reference interval were determined by quantile regression. Interobserver and intraobserver agreement was adequate with a coefficient of variation <10%. There were significant differences when comparing dogs with PH and the healthy group, as well as between the PH subgroups (P < .01), except between dogs with mild and moderate PH (P = .99). Only dogs in the severe PH group had TAPSE values that were mostly below the lower limit of the reference interval. CONCLUSIONS AND CLINICAL IMPORTANCE: TAPSE is easily obtainable with acceptable inter and intraobserver agreement. TAPSE is decreased in PH and below the reference interval in most dogs with severe PH.

Atrial-based pacing for sinus node dysfunction in dogs: initial results.

BACKGROUND: An important consideration for the treatment of sick sinus syndrome (SSS) lies in the function of the atrioventricular (AV) node because most patients with SSS retain the ability to conduct atrial impulses. HYPOTHESIS/OBJECTIVES: This retrospective study examined the feasibility of atrial pacing (AAI) in dogs with sinus node dysfunction (SND). ANIMALS: Sixteen dogs with SND and AAI pacing were identified. METHODS: Retrospective review of medical records. RESULTS: Follow-up time ranged from 45 to 1,227 days (mean: 292 days). Only 1 dog developed AV block 3 days postoperatively. Complete lead dislodgment occurred in 3/16 dogs 1, 19, and 27 days postoperatively. Lead perforation into the pericardial space occurred in 2/16 dogs. Rising thresholds for pacing with possible lead microdislodgment or fibrosis were suspected in another 3/16 dogs 57, 192, and 1,016 days after implantation. None of these dogs had complete loss of capture but all required higher thresholds for pacing. CONCLUSIONS AND CLINICAL IMPORTANCE: Based on this small group of dogs, clinically important AV block does not appear to occur in the long-term for dogs with SND. Risks of lead perforation, complete dislodgment, and rising thresholds for pacing, possibly because of microdislodgment, may be related to the initial skill level of the operator or the leads that were used. Use of leads with reduced torque at the lead tip, higher flexibility, increased lead-tip surface of contact with the endocardium or, more likely, use of alternate locations for pacing in the small right atrium of dogs with SND may decrease the frequency of these complications.

Combination therapy with digoxin and diltiazem controls ventricular rate in chronic atrial fibrillation in dogs better than digoxin or diltiazem monotherapy: a randomized crossover study in 18 dogs.

BACKGROUND: Atrial fibrillation (AF) with excessively high ventricular rates (VR) occurs in dogs with advanced heart disease. Rate control improves clinical signs in these patients. Optimal drug therapy and target VR remain poorly defined. HYPOTHESIS: Digoxin-diltiazem combination therapy reduces VR more than either drug alone in dogs with high VR AF. ANIMALS: Eighteen client-owned dogs (>15 kg) with advanced heart disease, AF, and average VR on 24-hour Holter > 140 beats per minute (bpm). METHODS: After baseline Holter recording, dogs were randomized to digoxin or diltiazem monotherapy, or combination therapy. Repeat Holter evaluation was obtained after 2 weeks; dogs were then crossed over to the other arm (monotherapy or combination therapy) for 2 weeks and a third Holter was acquired. Twenty-four hour average VR, absolute and relative VR changes from baseline, and percent time spent within prespecified VR ranges (>140, 100-140, and <100 bpm) were compared. Correlations between serum drug concentrations and VR were examined. RESULTS: Digoxin (median, 164 bpm) and diltiazem (median, 158 bpm) decreased VR from baseline (median, 194 bpm) less than the digoxin-diltiazem combination (median, 126 bpm) (P < .008 for each comparison). With digoxin-diltiazem, VR remained <140 bpm for 85% of the recording period, but remained >140 bpm for 88% of the recording period with either monotherapy. Serum drug concentrations did not correlate with VR. CONCLUSIONS AND CLINICAL IMPORTANCE: At the dosages used in this study, digoxin-diltiazem combination therapy provided a greater rate control than either drug alone in dogs with AF.

Lidocaine converts acute vagally associated atrial fibrillation to sinus rhythm in German Shepherd dogs with inherited arrhythmias.

BACKGROUND: Lidocaine is most frequently used to treat ventricular arrhythmias. However, lidocaine may have an antiarrhythmic effect for certain supraventricular arrhythmias. HYPOTHESIS: We hypothesized that lidocaine would be effective in converting experimentally induced atrial fibrillation (AF) to sinus rhythm and that a decrease in the dominant frequency (DF) and an increase in the organization as judged by the spectral entropy (SE) would occur over the course of the conversion. ANIMALS: Seven German Shepherd (GS) Dogs. METHODS: Dogs were anesthetized with fentanyl and pentobarbital. AF was induced with standard pacing protocols while left and right atrial monophasic action potentials (MAP) were recorded. The power spectra from the MAP recordings were analyzed to determine DF and SE during treatment with boluses of 2 mg/kg lidocaine. RESULTS: Lidocaine converted AF to sinus rhythm in all dogs and all episodes (n = 19). Conversion time was 27-87 seconds. After atropine, sustained AF was not induced; however, 5 episodes of atrial tachycardia resulted, and 3 were converted with lidocaine. Frequency domain analysis of 12 conversion sequences showed that left and right DF of the MAP signals decreased from the time of injection to conversion to sinus rhythm (P < .001). Mean SE indicated a gradient between the left and right atria (P = .003) that did not change during conversion. CONCLUSIONS AND CLINICAL IMPORTANCE: Vagally associated AF in GS dogs is terminated with lidocaine. Lidocaine is likely an effective treatment in clinical dogs with vagally associated AF.