Roberto A. Santilli

Objective: To evaluate the accuracy of recordings of atrial and ventricular depolarizations in 9-lead ECG of cats, with V1 placed at the right first intercostal space at the costochondral junction and V2 and V4 at the fifth or the sixth intercostal space (adjacent to the sternum and at the costochondral junction), and to assess the effect of age-related cardiac positional changes on ECG parameters. Methods: 60 healthy client-owned cats were planned to be enrolled from January 1, 2024, through December 31, 2024. Each cat underwent physical examination, thoracic radiography, 9-lead ECG, and echocardiography. Cats were age-grouped (< 5, 5 to 10, and > 10 years). The radiographic heart-sternum angle (HSA) in right lateral view was measured and correlated with ECG findings. Results: The V1 location enabled recording of negative P waves and QRS complexes with R/S ≤ 1, with significant intergroup differences (0.68 ms [IQR, 0.42], 0.37 ms [IQR, 0.32 ms], and 0.48 ms [IQR, 0.65 ms]; P = .04). In V2 and V4 in both sites, P waves were predominantly positive, and QRS complexes showed R/S > 1, with minimal intergroup differences. Aging was associated with a significant HSA reduction ( r = −0.72) but did not affect any clinically relevant ECG variables. Conclusions: This 9-lead system, with V1, V2, and V4 positioned as in dogs, enabled accurate P waves and QRS recording in cats. Aging reduced HSA without major effects on wave morphology. Clinical Relevance: This system will support detailed arrhythmias analysis in feline patients.

A 6‐year‐old, male, entire Chesapeake Bay retriever was referred for electrophysiological mapping and radiofrequency ablation for clinical incessant supraventricular tachycardia. A baseline electrocardiogram showed frequent paroxysms of a narrow QRS complex, regular tachycardia with a ventricular rate of 200 beats per minute, with an atrial rate of 330 beats per minute, variable atrioventricular conduction ratio and negative atrial depolarisation in inferior leads (II, III, aVF). According to the electrocardiographic findings, a tentative diagnosis of left atrial flutter was made, and an electrophysiological study was recommended. Left atrial endocardial mapping confirmed the presence of a macro‐reentrant tachycardia consistent with an atypical atrial flutter with a new site of a critical isthmus within the left interatrial septum. Ablation of the isthmus was not performed due to a technical issue, which necessitated a power‐controlled irrigated catheter instead of a temperature‐controlled usual catheter, and the owner's concerns regarding risk assessment for left side radiofrequency delivery with this methodology.

A 6‐month‐old golden retriever was referred for supraventricular tachycardia. Echocardiography showed a dilated cardiomyopathy phenotype of unknown aetiology. A 12‐lead electrocardiogram revealed a non‐sustained focal atrial tachycardia from the floor of the right atrium. Baseline 24‐h Holter monitoring showed frequent supraventricular ectopic beats organised in non‐sustained runs of focal atrial tachycardia. Endocardial mapping and 14 ablations of a wide ectopic focus at the opening of the caudal vena cava were performed. Endomyocardial biopsy findings revealed signs of active advancement of non‐inflammatory necrosis and degeneration. Post‐procedure, 24‐h Holter monitoring showed rare solitary premature ectopic atrial beats. One month after discharge without complications, the dog presented with mild ascites. Echocardiography revealed acquired stenosis of the caudal vena cava secondary to radiofrequency applications; iatrogenic Budd–Chiari syndrome was diagnosed based on computed tomography scans. A cover stent was placed at the caudal vena cava with clinical signs resolved at the 8‐month follow‐up.

In humans with arrhythmogenic cardiomyopathy (ACM) late-phase depolarization and repolarization abnormalities, such as epsilon (ɛ) waves and T wave inversion (TWI), are commonly observed in right precordial leads (V1-V3). This myocardial disorder has also been described in Boxer and English bulldogs (EBs), but data on electrocardiographic alterations in these breeds are lacking. The objective of this study was to describe electrocardiographic abnormalities in EBs with ACM, comparing QRS complexes and T waves with ≤ 5-year-old EBs without phenotypic expression of the disease. This is a retrospective study including 59 EBs (37 with ACM–ACM group and 22 healthy–healthy group). Standard echocardiographic, and 12-lead electrocardiogram data were retrospectively analyzed. In all leads QRS complex, R-peak time (RPT), and R peak-end time (RPE) were evaluated. Terminal activation duration (TAD), TWI, and presence of ɛ wave, defined as a positive small spike wave in right limb (aVR) and right precordial (V1) leads, were evaluated and compared with echocardiographic measurements. Arrhythmogenic cardiomyopathy group showed wider QRS complexes in all leads due to longer RPE (P < 0.05). The TAD in lead V1 was longer in ACM group (P < 0.001). The TWI and ɛ wave in ACM group were respectively present in 19% and 32%. Prolonged QRS complex and RPE in duration V1, the ɛ wave in lead aVR and V1, TWI and prolonged TAD in V1 were correlated with echocardiographic parameters defining right ventricular systolic function (P < 0.05). The presence of fragmented QRS complexes in limb and precordial leads, the prolongation of the RPE, the prolongation of TAD in V1, the presence of ɛ wave, can all be considered electrocardiographic features associated with ACM in EBs.

Background: Supraventricular tachycardias (SVTs), despite having various anatomical substrates and pathophysiological mechanisms, frequently show similar electrocardiographic presentations. Objectives: To locate and characterize atrial deflections (ADs) on 12-lead electrocardiograms in dogs with sustained rapid SVT and assess the utility of different electrocardiographic variables in differentiating types of tachycardia. Animals: Ninety-two dogs with orthodromic atrioventricular reciprocating tachycardia, 17 with atrial flutter, 33 with focal atrial tachycardia recorded and confirmed by electrophysiological study, and 40 dogs with sinus tachycardia. Methods: Atrial deflection position on the 12-lead surface electrocardiogram was assessed according to the sequence of intracardiac activation. Its features were evaluated together with the relationship between AD and QRS complex interval (AD-R) and QRS complex and AD interval (R-AD). Results: Orthodromic atrioventricular reciprocating tachycardia was characterized by an AD-AD interval of 213 ± 30 ms, mean electrical axis (MEA) of AD of −90 (−90/−78)°, R-AD interval of 75 (65-80) ms, and R-AD/AD-R of 0.54 (0.45-0.64). Atrial flutter was characterized by an AD-AD interval of 199 ± 57 ms, MEA of 76° (72/81), R-AD of 120 (72-144) ms, and R-AD/AD-R of 0.81 (0.63-1.13). Focal atrial tachycardia was characterized by an AD-AD interval of 270 ± 38 ms, MEA of 49 (−72/76)°, R-AD of 160 (120-200) ms, and R-AD/AD-R of 1.45 (0.92-1.67). Sinus tachycardia was characterized by an AD-AD interval of 292 ± 31 ms, MEA of 66° (52/73), R-AD of 215 (192-222) ms, and R-AD/AD-R of 2.68 (2.25-3.08). Conclusions and Clinical Importance: Analyzing AD on 12-lead electrocardiogram is helpful in differentiating the most common SVTs in dogs.

Standard transthoracic echocardiography is considered the non-invasive gold standard for the diagnosis of most cardiac diseases. Defining reproducibility, repeatability, and reliability of this exam is imperative to reduce errors in clinical evaluations. The present study aimed at: (1) evaluating the reproducibility and repeatability of 15 echocardiographic parameters in dogs by analyzing measurements obtained from several operators with different levels of experience and comparing them to the ones obtained from two board-certified operators (gold standards - GSs); (2) assessing whether different formative paths have an influence on the variability of the echocardiographic measurements. Fifty-one operators have been included in this study, along with two diplomates of the European College of Veterinary Internal Medicine - Cardiology. Ten dogs were enrolled, 5 Golden Retrievers and 5 Cavalier King Charles Spaniels. Echocardiographic examination was performed on each dog by one GS and several operators on the same day. Results show the highest deviation from the GS and a poor inter-operator reproducibility for the M-mode measurements of the interventricular septum and the left ventricular free wall. Differently, M-mode-obtained internal diameters of the left ventricle in systole and diastole, and measurements of the aortic annulus and root show moderate to excellent intra- and inter-operator reliability and a good concordance with the GSs, demonstrating that all the operators correctly assess left ventricular systolic function and dilation, and evaluate the aortic valve. Furthermore, a specialist clinical activity, more than the acquired theoretical knowledge, affects the reliability of the echocardiographic examination by reducing the difference from the GS’ measurements.

Background: There is a lack of clinical data on hypertrophic cardiomyopathy (HCM) in dogs. Hypothesis/Objectives: To investigate signalment, clinical signs, diagnostic findings, and survival in dogs with HCM. Animals: Sixty-eight client-owned dogs. Methods: Retrospective multicenter study. Medical records were searched between 2003 and 2015. The diagnosis of left ventricular (LV) hypertrophy was made by echocardiographic examination. Results: Three hundred and forty-five dogs with LV hypertrophy were identified, of which 277 were excluded. The remaining 68 dogs were 0.3 to 14 years old and predominantly <10 kg (85%), and without a sex predilection. Twenty-four % were Shih Tzu and 24% terrier breeds. Most (80%) had a systolic heart murmur. Owner-determined exercise intolerance (37%) and syncope (18%) were most commonly reported signs. The majority (84%) of dogs had symmetrical LV hypertrophy, whereas asymmetrical septal and LV free wall hypertrophy was observed in 9% and 6% of dogs, respectively. Isolated basal interventricular septal hypertrophy was not observed. Commonly recorded were systolic anterior motion of the mitral valve (60%) and LV diastolic dysfunction (89% of dogs where diastolic function was evaluated). Six dogs died unexpectedly, and 3 developed congestive heart failure. Known survival times were between 1 day and 114 months after diagnosis. Conclusions and Clinical Importance: Hypertrophic cardiomyopathy in dogs should be considered as a differential diagnosis if LV hypertrophy is identified. Small breed dogs are overrepresented, and it is uncommon for dogs with HCM to develop CHF although sudden death can occur.