Effect of acute haemorrhage on QRS amplitude of the lead II canine electrocardiogram

OBJECTIVE: To examine the effect of acute haemorrhage on the QRS amplitude of the canine lead II surface electrocardiograph (ECG). DESIGN: Ten adult racing Greyhounds were tranquilised, anaesthetised, positioned in right lateral recumbency and connected to recording electrodes of an ECG unit. Baseline six-lead ECG traces were recorded, and further traces were obtained after one unit (460 mL) of blood, and then a second unit, were collected from the femoral artery. RESULTS: There was a consistent and progressive reduction in amplitude of the QRS complex in all leads during acute haemorrhage. QRS amplitude in lead II after removal of two units of blood averaged 74% of the baseline voltage, with individual values of 61 to 91% (P < 0.0001). There were even greater reductions in QRS amplitudes in lead aVL during haemorrhage. In three additional dogs, reductions in QRS voltages were shown to be accompanied by reductions in end-diastolic left ventricular internal dimensions measured echocardiographically. Furthermore, the effects of haemorrhage on the QRS amplitude and echocardiographic measurements were reversed when circulating blood volume was restored by re-infusion of blood removed previously. CONCLUSION: Acute haemorrhage corresponding to an approximately one-third reduction in blood volume caused a substantial reduction in QRS voltage of the surface ECG. It is postulated that this resulted from diminished ventricular distension as a consequence of reduced venous return. A similar mechanism may account for the small-amplitude ECG complexes associated with pericardial effusion, severe dehydration and hypovolaemia.     

Morphology of ventricular arrhythmias in the boxer as measured by 12-lead electrocardiography with pace-mapping comparison

The QRS amplitude and polarity were determined in 12-lead electrocardiograms recorded from 22 Boxers with ventricular arrhythmias. Eighty-one percent (18/22) of dogs displayed a positive QRS morphology in the caudoventral leads (II, III, and aVF) and 77% (17/22) of dogs displayed a positive QRS morphology in the left precordial leads (V2-V6). In leads I and V1, the polarity of the QRS complex was variable (positive or negative). To determine if these morphologic features were suggestive of ventricular complexes arising from the right or left ventricle, a comparison was made to the QRS complexes in a pace-mapping study performed in 7 healthy mixed-breed dogs. A total of 3 right and 4 left ventricular sites were paced. None of the left ventricular paced sites resulted in a QRS morphology similar to the most common spontaneous ventricular arrhythmia in the Boxers. In contrast, QRS morphology in each of the 3 right ventricular sites was similar to that observed in the Boxers (P < .033). Each of these produced positive deflections in the caudoventral and left precordial leads, but both positive and negative QRS complexes were observed in leads I and V1 only when the right ventricular septum was paced. This finding suggested that the right ventricular septum might be a site of origin for the ventricular rhythm observed in the Boxers because in the Boxers the polarity of leads I and V1 also varied. Pacing the right ventricular outflow tract always resulted in a negative QRS complex in lead 1, whereas pacing the right ventricular apex always resulted in a positive QRS complex in lead I and a negative QRS complex in V1. However, these locations cannot be excluded as possible sites of origin for the spontaneous ventricular arrhythmias in the Boxers because the arrhythmias could be originating from both of these locations. The spontaneous ventricular arrhythmia of the Boxer is most similar to that of paced ventricular rhythms arising from the right ventricle. More precise localization to a region of the right ventricle such as outflow tract, septal, or apical could not be made.     

Cardiac evaluation of anesthetized Grevy's zebras (Equus grevyi)

OBJECTIVE: To determine ECG and echocardiographic measurements in healthy anesthetized Grevy's zebras (Equus grevyi). ANIMALS: 20 healthy zebras. PROCEDURES: Auscultation, base-apex ECG, and echocardiography were performed on anesthetized zebras. RESULTS: Low-grade systolic murmurs were detected in the left basilar region in 4 of 20 zebras. Evaluation of ECGs from 19 zebras revealed sinus rhythm with a predominantly negative QRS complex and a mean +/- SD heart rate of 67 +/- 10 beats/min. Echocardiograms of sufficient image quality were obtained for 16 zebras. Interventricular septal thickness in diastole, left ventricular chamber in diastole and systole, left atrial diameter, and left ventricular mass were significantly and moderately correlated with estimated body weight (r values ranged from 0.650 to 0.884). Detectable swirling of blood in the right and sometimes the left ventricles was detected in 9 of 16 zebras, whereas physiologic regurgitation of blood was detected for the aortic valve in 3 zebras, pulmonary valve in 2 zebras, mitral valve in 2 zebras, and tricuspid valve in 1 zebra. CONCLUSIONS AND CLINICAL RELEVANCE: Results of this study provide reference information for use in the cardiac evaluation of anesthetized Grevy's zebras.     

Effects of endurance training on standard and signal-averaged electrocardiograms of sled dogs

OBJECTIVE: To determine the effect of endurance training on QRS duration, QRS-wave amplitude, and QT interval. ANIMALS: 100 sled dogs in Alaska. PROCEDURE: Dogs were examined in early September (before training) and late March (after training). During the interim, dogs trained by pulling a sled with a musher (mean, 20 km/d). Standard and signal-averaged ECG were obtained before and after training. RESULTS: Endurance training significantly increased mean QRS duration by 4.4 milliseconds for standard ECG (mean +/- SEM; 62.3 +/- 0.7 to 66.7 +/- 0.6 milliseconds) and 4.3 milliseconds for signal-averaged ECG (51.5 +/- 0.7 to 55.8 +/- 0.6 milliseconds) without changing body weight. Increase in QRS duration corresponded to a calculated increase in heart weight (standard ECG, 23%; signal-averaged ECG, 27%). Signal-averaged QRS duration was correlated with echocardiographically determined left ventricular diastolic diameter for the X orthogonal lead (r = +0.41), Y orthogonal lead (r = +0.33), and vector (r = +0.35). Training also increased QT interval (234 +/- 2 to 249 +/- 2 milliseconds) and R-wave amplitude in leads II and rV2, increased peak-to-peak voltage and S-wave amplitude in the Y orthogonal lead, and decreased Q-wave amplitude in the Y orthogonal lead. CONCLUSIONS AND CLINICAL RELEVANCE: Electrocardiographic changes reflected physiologic cardiac hypertrophy in these canine athletes in response to repetitive endurance exercise. The QRS duration increases in response to endurance exercise training and, therefore, may be of use in predicting performance in endurance activities.     

A Study of Electrocardiographic Patterns in a Population of Commercial Broiler Chickens

Olkowski, A.A., Classen, H.L., Riddell, C. and Bennett, C.D., 1997. A study of electrocardiographic patterns in a population of commercial broiler chickens. Veterinary Research Communications, 21 (1), 51-62. A study was completed to characterize the electrocardiographic (ECG) patterns of male broiler chickens. Data were collected from 300 commercial broilers. ECG readings were collected from all birds between 12 and 15 days of age and then twice more at 10-day intervals. The measurements included heart rate and rhythm, QRS complex duration, amplitude and mean electrical axis (MEA), incidence of ascites and incidence of sudden death syndrome (SDS). Eight birds died from SDS and 4 birds died from ascites. Twelve birds were condemned for ascites at the processing plant. The overall population heart rate declined with age. Birds that died of SDS had a higher heart rate, whereas those that developed ascites had a lower heart rate than the remainder of the population. The normal MEA was found to be between 0° and 180°. On average 30% of birds showed left or right QRS axis deviation, and this pattern was observed in 14 of the 16 birds that developed ascites. Several types of cardiac arrhythmias were observed, the most common being premature ventricular contractions (PVC). The incidence of PVC increased with age, ranging from 1% at 12-15 days of age to 8.9% at 32-35 days of age. QRS axis deviation was present in 5 SDS birds. It is concluded that some 30% of the broiler flock tested was at risk of developing heart failure or heart-related disease.     

Echocardiography of the normal bovine heart: technique and ultrasonographic appearance

Fifty-one clinically healthy cows were examined ultrasonographically from the third and fourth intercostal spaces on both sides of the thorax. A 3.0 MHz transducer was used and the heart was examined in the caudal long, caudal short and cranial long axes on the right side, and in the caudal and cranial long axes on the left side. In each position the optimal transducer orientation and the images of the structures were recorded. In the caudal long axis view of the heart on the right (transducer positioned at the fourth intercostal space), all four chambers were visible with the transducer positioned 8 to 10 cm dorsal to the level of the olecranon. The left ventricular outflow tract, consisting of the aortic valve and ascending aorta, were visible in the same position with the transducer rotated 10 to 40 degrees clockwise. In the caudal short axis view of the heart on the right, the left and right ventricles were visible in cross-section with the transducer held at right angles to the ribs in the fourth intercostal space, 3 to 6 cm dorsal to the olecranon and tipped slightly dorsally. In the cranial long axis view of the heart on the right, the right ventricular outflow tract, consisting of the pulmonary valve and pulmonary artery, was visible in the third intercostal space, 8 to 10 cm dorsal to the olecranon with the transducer angled craniodorsally and rotated 10 to 20 degrees clockwise. In the caudal long axis view of the heart on the left, the left and right ventricles and the left ventricular outflow tract were visible with the transducer placed in the fourth intercostal space. In the cranial long axis view on the left, the right ventricular outflow tract was visible.     

Gene expression of endothelin-1 and its receptors in the heart of broiler chickens with T(3)-induced pulmonary hypertension

To investigate the effect of T₃-induced pulmonary hypertension on endothelin (ET) production and genes expression of ET-1, ET_A and ET_B receptors (ET_AR and ET_BR) during rearing, semiquantitative RT-PCR and enzyme immunometric assay were performed in the heart ventricles and serum, respectively. The ET-1 and its receptor genes were expressed in the right and left ventricles of control and T₃-treated broilers at 12, 28 and 49 days of age. There were significant (P < 0.05) reductions of the relative amounts of ET-1 (in both ventricles) and ET_AR (in the right ventricle) mRNAs at 28 and 49 days of age, in T₃-treated broilers compared to controls. The relative amounts of ET_BR mRNA in the right and left ventricles did not significantly differ between control and T₃-treated broilers at any age. The serum level of ET was significantly (P < 0.05) increased in T₃-treated chickens at 28 and 49 days of age when compared with that of the control. It is concluded that ET-1, ET_AR and ET_BR genes are normally expressed in the heart ventricles of broilers. It is likely that increased serum level of ET and decreased ET-1/ET_AR genes expression in the ventricles are involved in the heart dysfunction of broiler chickens with developmental pulmonary hypertension.     

Determination of heart dimensions in cattle via 2-D-mode echocardiography

The goal of this study was to determine via echocardiography the size of the left and right cardiac ventricles and the width of the interventricular septum and the left free ventricular wall in 51 healthy cows. The heart regions were examined in standing cows using a 3.0 Mhz sector transducer in 2-D-Mode. The dimensions of the heart were measured in the caudal long and short axes on the right side and in the caudal and cranial long axes on the left. The diameter of the ventricles was determined in a plane immediately beneath the mitral or tricuspid valves and that of the aorta and pulmonary artery in a plane immediately above the aortic and pulmonary valves, respectively. At the end of the study, all of the cows were slaughtered, the hearts were removed and the same parameters were determined using a tape measure. Results of in vivo and in vitro measurements were compared. In the right caudal long axis, the diameters of the left ventricle during both diastole (x +/- s = 7.0 +/- 0.73 cm) and systole (4.5 +/- 0.69 cm) were larger than those of the right ventricle during diastole (4.1 +/- 1.02 cm) and systole (3.6 +/- 0.98 cm). The diameter of the ventricles during diastole was larger than that during systole. Analogous results were obtained in both other axes. The diameter of the right ventricle during systole was larger when measured in the right caudal long axis (3.6 +/- 0.98 cm) than in the right caudal short axis (3.2 +/- 1.15 cm). This was also true for measurements obtained during diastole. The interventricular septum and the left ventricular wall were thicker during systole than during diastole. The diameter of the pulmonary artery was larger during diastole (5.6 +/- 0.82 cm) than systole (5.2 +/- 0.84 cm). The diameter of the aorta was smaller than that of the pulmonary artery and did not change significantly during diastole (4.9 +/- 0.92 cm) and systole (4.8 +/- 0.80 cm). The diameters of both ventricles measured at post mortem were smaller than those measured in vivo during diastole and larger than those measured during systole. There were no significant differences between the measurements performed twice, three days apart, in 11 of the cows.     

Congenital cardiac disease in dogs

Patent ductus arteriosus, aortic stenosis, ventricular septal defect, pulmonic stenosis and tetralogy of Fallot are the most frequently reported cardiac anomalies of dogs. Systolic murmurs occur after the first heart sound but before the second, while diastolic murmurs occur after the second heart sound. Murmurs associated with the pulmonic, aortic and mitral valves are best heard at the left intercostal spaces 3, 4 and 5, respectively, and those of the tricuspid valve at the right intercostal space 3 or 4. Mucosae at both ends of the animal should be examined for cyanosis. Right ventricular enlargement is characterized by a mean electrical axis greater than 100 degrees, a Q wave amplitude greater than 0.5 mv in leads II, III and AVF, and a positive T wave in lead V10. Left ventricular enlargement causes an axis of less than 40 degrees, a QRS complex duration greater than 0.06 seconds, an R wave amplitude greater than 3 mv, and a slurred or depressed ST segment. Atrial enlargement is characterized by a P wave duration greater than 0.04 seconds and a P wave amplitude greater than 0.4 mv. The cardiac silhouette is more upright and round on DV radiographs than on VD projections.     

Electrocardiographic changes in the growing Mastín Español

Serial electrocardiograms were recorded from 70 Mastín Español dogs in right lateral recumbency, aged between one day and three years, in order to observe the changes in the waveform and intervals, QRS morphology, cardiac rhythm and heart rate caused by their growth. Age and bodyweight caused a gradual increase in the duration and amplitude of the P wave, duration of the PR, QT and RR intervals, amplitude of the R wave and duration of the QRS complex and ST segment. Q wave was observed in nearly all the recordings with different amplitudes. The S wave was only significant in one-day-old animals and QRS morphology showed significant important changes from qrS and rS to qR and qRs morphologies during the first two weeks of life. The T wave increased its amplitude until the age of two months and changed its polarity (from negative to positive) from five months of age onwards. The heart rate decreased until the age of seven months, reaching stabilised values of 110 ± 7-3 beats per minute. Sinus tachycardia was commonplace in animals under one month old and respiratory sinus arrhythmia was found from six months of age. Sex only influenced the duration and amplitude of the T wave. Males had higher mean values than females.     

Macroscopic anatomy of the heart of the ringed seal (Phoca hispida)

Anatomical properties of the ringed seal (Phoca hispida) heart and associated blood vessels reveal adaptations related to requirements for diving. Seven adult ringed seals were embalmed and dissected to document the gross anatomical features of the heart. Computed tomography images of the thoracic cavity were taken on one seal prior to dissection. The shape and position of the heart is different from the typical carnivore heart. The most notable difference is its dorsoventral flattened appearance with its right and left sides positioned, respectively, within the thoracic cavity. The long axis of the heart is positioned horizontally, parallel to the sternum. The right ventricle is spacious with thin walls which extend caudally to the apex of the heart such that the apex is comprised of both right and left ventricles. The cusps of the left atrioventricular valve of the ringed seal heart resemble an uninterrupted, circular curtain making it challenging to distinguish the divisions into parietal and septal cusps.     

Ventricular dyssynchrony as a cause of structural disease in the heart of Dorper sheep

Ventricular dyssynchrony is a disturbance of the normal, organized electromechanical coupling of the two ventricles. This condition has many causes, such as left bundle branch block, ventricular preexcitation, right ventricular pacing and right ventricular premature ventricular complexes (PVCs). Ventricular dyssynchrony has many adverse haemodynamic effects on the left ventricle and we wanted to know whether these adverse haemodynamic effects might have any structural consequences on the left ventricles of such hearts. Six healthy Dorper wethers were subjected to numerous right ventricular PVCs to induce ventricular dyssynchrony in order to determine whether any structural consequences will occur in the left ventricles of these hearts. Myocarditis in the musculature of the left ventricles of all six these hearts was seen.     

Invasive pressure measuring for the determination of the aortic opening surface in normal and stenotic left ventricular outflow tracts

A method of evaluation of the aortic opening area in healthy dogs and dogs with aortic stenosis is described. Through right and left heart catheterisation intraventricular and intravascular pressures were measured. For the determination of cardiac output the thermodilution technique is used. The aortic opening area is calculated by using the GORLIN-formula. Values of normal and stenotic left ventricular outflow opening area are given.     

Congestive heart failure associated with myxomatous degeneration of the left atrioventricular valve in a parakeet

Congestive heart failure was diagnosed in a 27-year-old Indian ringneck parakeet with exercise-induced dyspnea. A grade IV/VI holosystolic murmur that radiated to the right sternal area was auscultated over the left side of the sternum. Radiography revealed progressive cardiomegaly, hepatomegaly, pulmonary edema, and accumulation of fluid within the coelomic cavity. Echocardiography revealed biatrial enlargement and enlargement of the right ventricle. Doppler recording revealed high velocity left and right atrioventricular valve regurgitation. Treatment with digoxin and furosemide alleviated clinical signs for approximately 10 months. Gross postmortem examination revealed cardiac enlargement and eccentric hypertrophy of both ventricles on cross-section. Pulmonary congestion and edema, hepatomegaly, hepatic congestion, and ascites were also evident. Histologic examination of the heart revealed myxomatous degeneration of the left atrioventricular valve, muscular hypertrophy of the right atrioventricular valve, and biventricular chronic myofiber degeneration and necrosis.     

Effects of graded pleural effusion on QRS in the dog

Six anesthetized healthy dogs were placed in right lateral recumbency. Electrocardiographic leads I, aVF, V10, rV3, V3, and V5 were obtained during a control period and after introduction of pleural effusions ranging between 0.66 and 55 ml of isotonic saline solution/kg of body weight. Peak-to-peak amplitudes of QRS were measured, and the effusion required to decrease this amplitude by more than 1 SD from the mean of healthy dogs was determined for each lead tested. Sensitivity of detecting pleural effusion was greatest in lead I in which an effusion of 2.75 ml/kg could be detected. The QRS amplitudes in leads V10 and aVF were decreased to a significant level only at large effusions. Leads V3 and V5 were "blind," even to the greatest pleural effusions. Radiographs taken with the graded pleural effusion documented that the heart "floated" away from rV3 and toward V3 and V5, thus explaining the sensitivity of rV3 and insensitivities of V3 and V5. It seems that pleural effusion can be detected by using these leads in dogs in right lateral recumbency, that detection is best if serial recordings are taken, and that relatively high sensitivities are achieved using lead I.     

Cause of heart murmurs in 57 apparently healthy cats

Heart murmurs are caused by turbulent blood flow or by vibration of cardiac structures. Turbulent blood flow may originate from structural heart disease or from physiological phenomena. The aims of this study were to establish the cause of heart murmurs in apparently healthy adult cats and to determine whether a heart murmur is a reliable indicator of heart disease. In this retrospective study, we reviewed the medical records of cats in which a heart murmur was detected during physical examination by one of the authors in the period January 2008 to December 2009. Cats younger than 6 months and those with systemic disease were excluded. Timing, grade, and point of maximum intensity of the murmur were determined by one observer (MD) before 2D-, M-mode and Doppler echocardiography. Fifty-seven cats (median age 76 months, range 6-194) were included, 30 neutered females and 27 neutered males. All murmurs were systolic and varied in intensity from 2/6 to 5/6. The point of maximum intensity was the left or right parasternal region in 34/57 (61%) of murmurs. Murmurs were caused by dynamic left ventricular outflow tract obstruction in 25/57 (44%) cats, dynamic right ventricular outflow tract obstruction in 9/57 (16%) cats, and combined dynamic left and right outflow tract obstruction in 11/57 (19%) cats. In 5 (9%) cats the cause of the murmur could not be identified. Heart disease was present in 50 (88%) cats, namely, left ventricular hypertrophy in 44 (77%) and congenital defects in 6 (11%) cats. In conclusion, most heart murmurs in apparently healthy cats are detected in the left or right parasternal region and are caused by dynamic left and right ventricular outflow tract obstruction. Because most cats (88%) with a heart murmur had heart disease in this study, if a heart murmur is detected in an apparently healthy cat, echocardiography is recommended to determine the cause of the heart murmur and the presence of heart disease.     

Orthodromic atrioventricular reciprocating tachycardia conducted with intraventricular conduction disturbance mimicking ventricular tachycardia in an English Bulldog

Electrocardiographic tracings of an English Bulldog referred for cardiogenic shock due to an orthodromic atrioventricular reciprocating tachycardia conducted with intraventricular conduction disturbance and mimicking ventricular tachycardia (VT) are presented. At admission the surface ECG showed a wide QRS complex tachycardia (WCT) that was converted to sinus rhythm using manual cardioversion (chest thump). This change revealed pre-existing right bundle branch block, and a final diagnosis of supraventricular tachycardia (SVT) with intraventricular conduction disturbance was made. Electrophysiologic study defined the SVT mechanism as an atrioventricular macroreentrant tachycardia mediated by a single mid-septal accessory pathway. The differentiation between various types of WCT is essential when antiarrhythmic therapy is considered. The surface ECG should be systematically evaluated in order to recognize the characteristic features of SVT and VT. Moreover chest thump procedure can be very helpful in the attempt to convert the rhythm to sinus rhythm and to correctly recognize the underlying arrhythmia.     

Effect of hyperlipidemia on cardiovascular responses to adrenergic stimulation in piglets.

This study was designed to assess the effect of hyperlipidemia on cardiovascular responses to adrenergic stimulation in a porcine model. Four-week-old piglets (n = 10) were divided into two groups; one fed a control diet and the other was fed an atherogenic diet for 8 weeks. Cardiovascular responses were evaluated to both norepinephrine (NE; 0.5 and 2.5 micrograms/kg) and isoproterenol (ISO; 0.1 and 0.5 microgram/kg) from simultaneous recordings of femoral arterial pressure, heart rate, left intraventricular pressure and left intraventricular dP/dt. It was found that no significant difference in the baseline values of cardiovascular function was observed between the control and hyperlipidemic groups. However, in the hyperlipidemic group as compared with the control group: 1) arterial blood pressure responses to NE were significantly increased (P less than 0.05), 2) cardiac contractile responses to NE and ISO were significantly potentiated (P less than 0.05), and 3) reflex bradycardia in response to increasing arterial blood pressure did not occur. These findings indicate that hyperlipidemia can potentiate the cardiovascular responses to adrenergic stimulation, whereas reflex cardiovascular regulation is somewhat altered by hyperlipidemia. Conceivably, these observations may have relevance to the possible role of the mechanism of the interaction of hyperlipidemia and hypertension in atherogenesis.     

Method of selective and non-selective angiocardiography for the horse

A practical and safe method of angiocardiography for the horse is described. The technique involved the rapid injection of 50 to 150 ml contrast agent via catheters in the right and left heart, pulmonary artery and aorta. The examination was carried out with the horse in the standing position or under general anaesthesia. Angiocardiograms were performed on 10 normal horses and satisfactory pictures of the right and left ventricles, pulmonary arteries, aorta and coronary circulation were obtained. The technique was also used in a foal with severe congenital heart disease. The most practical methods of recording the images in the standing position were cinefilm or video taperecording. In the recumbent position both cinefilm and radiographs were taken. No damage to the heart was inflicted by the catheters and only a few ventricular premature contractions (less than five) were produced by the pressure of injection. No signs of toxicity were recorded using repeated injections of contrast material (ie, less than 600 ml).