The electrocardiogram of unanesthetized cats fixed in a net

Electrocardiograms by standard limb lead, augumented unipolar limb lead and AB (Apex-Base) lead were recorded from 24 unanesthetized adult cats from a SPF closed colony. The unanesthetized cats were held in the sternal position or in the right lateral recumbent position by means of a net. The mean electrical axes of P, QRS and T waves were calculated on the basis of values of I, II and III leads. The ECG patterns and mean electrical axes were compared between the sternal position and the right lateral recumbent position. The results are summarized as follows. The mean values of RR duration, P wave duration, QRS complex duration, T wave duration, PQ interval and QT interval were 0.432, 0.033, 0.027, 0.101, 0.076 and 0.183 seconds, respectively. The values of duration, interval and amplitude were not prominently influenced by the change in posture. The ECG shape had a definite configuration on each lead except that leads I and a VL showed unstable patterns. Notches and R' waves appeared in every lead in many cases. There was a positive linear correlation between RR and QT duration: r = 0.798 in the sternal position and r = 0.525 in the right lateral recumbent position. The angle of QRS mean electrical axis on the horizontal plane was 66.90 degrees +/- 26.05 (SD) in the sternal position and 41.84 degrees +/- 75.23 (SD) in the right lateral recumbent position. The P and T mean electrical axes showed small variations.     

The electrocardiogram of normal ferrets and ferrets with right ventricular hypertrophy

Sixty-eight electrocardiograms were recorded on ferrets (Mustela putorius furo). These represent 29 normal weanling males, 19 normal adult males and 20 adult males with right ventricular hypertrophy (RVH). Analyses of rate, rhythm, axis and total voltage were used to define the normal electrocardiogram (ECG) and to identify changes seen in RVH. The normal ferret has a heart rate of about 300 beats per minute and a mean electrical axis of + 86 degrees +/- 6.6 (SD). A 56% increase in right ventricular weight to body weight ratio was not associated with right axis deviation. The overall voltage produced on the ECG was increased in the group with RVH as compared to the normal group (p less than 0.030).     

Effects of body position on intracranial and cerebral perfusion pressures in isoflurane-anesthetized horses.

Inhalant anesthetics may interfere with normal cerebrovascular autoregulation. It was, therefore, hypothesized that intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in isoflurane-anesthetized horses would be especially sensitive to body and head position because of the potential for large hydrostatic gradients between the brain and heart in this species. Anesthesia was induced and maintained in six clinically healthy, unmedicated geldings with 1.57% isoflurane in O(2); mechanical ventilation was used to maintain normocapnia. ICP was measured by using a subarachnoid strain-gauge transducer. Blood gases and carotid arterial, right atrial, and airway pressures were also measured. Five body positions were studied in semirandomized order: dorsal recumbency (DR) with head down (HD), DR with head level (HL), lateral recumbency (LR), sternal recumbency (SR) with HL, and SR with head up (HU). Data were analyzed by using paired t-tests. ICP and CPP values, respectively, are as follows (means +/- SD): 36 +/- 4 and 55 +/- 18 mmHg (DR-HD); 34 +/- 6 and 51 +/- 32 mmHg (DR-HL); 24 +/- 5 and 48 +/- 4 mmHg (LR); 19 +/- 11 and 87 +/- 12 mmHg (SR-HL); and -14 +/- 7 and 71 +/- 10 mmHg (SR-HU). Significant differences were found among all positions, except for SR-HL vs. LR. Significant increases in CPP were observed only in sternal positions. In conclusion, ICP in isoflurane-anesthetized horses changes inversely with the brain-to-heart hydrostatic gradient. DR may also cause increases in ICP, irrespective of head position.     

Pleural pressure as a function of body position in rabbits

Pleural pressure was measured at end expiration in spontaneously breathing anesthetized rabbits. A liquid-filled capsule was implanted into a rib to measure pleural liquid pressure with minimal distortion of the pleural space. Capsule position relative to lung height was measured from thoracic radiographs. Measurements were made when the rabbits were in the prone, supine, right lateral, and left lateral positions. Average lung heights in the prone and supine positions were 4.21 +/- 0.58 and 4.42 +/- 0.51 (SD) cm, respectively (n = 7). Pleural pressure was -2.60 +/- 1.87 (SD) cmH2O at 50.2 +/- 7.75% lung height in the prone position and -3.10 +/- 1.22 cmH2O at 51.4 +/- 6.75% lung height in the supine position. There was no difference between the values recorded in the prone and supine positions. Placement of the capsule into the right or left chest had no effect on the magnitude of the pleural pressure recorded in rabbits in right and left lateral recumbency (n = 12). Measurements over the nondependent lung were repeatable when rabbits were turned between the right and left lateral positions. Lung height in laterally recumbent rabbits averaged 4.55 +/- 0.52 (SD) cm.     

Electrocardiograms recorded from the body surface of the carp, Cyprinus carpio

The electrocardiograms (ECGs) in five kinds of bipolar leads were recorded from the body surface of the carp under water. Each component constituting the ECG wave could be detected by the present method. The potentials of the ECGs recorded by the present method were relatively small, the values being 2-64 microV. The electrical axis in most carp was directed toward the right lateral side.     

Venous hydrostatic indifference point as a marker of postnatal adaptation to orthostasis in swine.

The postulate that venous adaptation assists postural baroreflex regulation by shifting the hydrostatic indifference point (HIP) toward the heart was investigated in eight midazolam-sedated newborn piglets. Whole body head-up (+15, +30, and +45 degrees ) and head-down (-15 and -30 degrees ) tilt provided a physiological range of orthostatic strain. HIP for all positive tilts shifted toward the heart (P < 0.05), +45 degrees HIP shifted most [6.7 +/- 0.3, 5.9 +/- 0.5, and 3.6 +/- 0.3 (SE) cm caudal to right atrium on days 1, 3, and 6, respectively]. HIP for negative tilts (3.0 +/- 0.2 cm caudal to right atrium) did not shift with postnatal age. Euthanasia on day 6 caused 2.1 +/- 0.3-cm caudal displacement of HIP for positive and negative tilts (P < 0.05). HIP proximity to right atrium was not altered by alpha-, beta-adrenoceptor and cholinoceptor blockade on day 5. It is concluded that early HIP migration reflects enhancement of venous pressure control to head-up orthostatic strain. The effect is independent of baroreflex-mediated adrenoceptor and cholinoceptor mechanisms.     

Improved ECG detection of presence and severity of right ventricular pressure load validated with cardiac magnetic resonance imaging

The study aimed to assess whether the 12-lead ECG-derived ventricular gradient, a vectorial representation of ventricular action potential duration heterogeneity directed toward the area of shortest action potential duration, can improve ECG diagnosis of chronic right ventricular (RV) pressure load. ECGs from 72 pulmonary arterial hypertension patients recorded <30 days before onset of therapy were compared with ECGs from matched healthy control subjects (n = 144). Conventional ECG criteria for increased RV pressure load were compared with the ventricular gradient. In 38 patients a cardiac magnetic resonance (CMR) study had been performed within 24 h of the ECG. By multivariable analysis, combined use of conventional ECG parameters (rsr' or rsR' in V1, R/S > 1 with R > 0.5 mV in V1, and QRS axis >90 degrees ) had a sensitivity of 89% and a specificity of 93% for presence of chronic RV pressure load. However, the ventricular gradient not only had a higher diagnostic accuracy for chronic RV pressure load by receiver operating characteristic analysis [areas under the curve (AUC) = 0.993, SE 0.004 vs. AUC = 0.945, SE 0.021, P < 0.05], but also discriminated between mild-to-moderate and severe RV pressure load. CMR identified an inverse relation between the ventricular gradient and RV mass, and a trend toward a similar relation with RV volume. In conclusion, chronically increased RV pressure load is electrocardiographically reflected by an altered ventricular gradient associated with RV remodeling-related changes in ventricular action potential duration heterogeneity. The use of the ventricular gradient allows ECG detection of even mildly increased RV pressure load.     

Heart rate in caged Macaca fascicularis. Effects of short-term physical exercise.

Electrocardiograms were recorded hourly for five days in 16 caged Macaca fascicularis by means of a miniaturized ECG transmitter connected to two chest leads. The lowest heart rates were 135 +/- 35 (mean +/- SD, n= 31) beats/min at 5 a.m., and the highest were 192 +/- 22 (n = 29) beats/min at 3 p.m. Sinus arrhythmia was common. Eight of the animals were trained to exercise in a specially designed enclosed treadmill; their heart rates were recorded daily during two 10-min periods of running at 3.4 km/h. Transfer of the monkeys (n k0) to the treadmill increased heart rate from 186 +/- 24 to 228 +/- 23 beats/min; exercise further increased it to 271 +/- 8 beats/min.     

Hypoglycemia of squirrel monkey neonates: implications for infant survival

Neonatal deaths are a serious problem in breeding colonies of squirrel monkeys. Seriously ill neonates in our colony are always hypoglycemic on presentation. To determine normal glucose values for squirrel monkey infants of various ages, serum glucose determinations were done at 1, 3, 7, 10, 14 days and 1 month of age using a standard laboratory test for serum glucose. Glucose concentration increased from a low of 49 +/- 3 mg/dl (Mean +/- SEM) at 1 day (n = 21) to 109 +/- 4 mg/dl at 1 month of age (n = 17). Glucose values for 1, 3 and 7 day-old infants were significantly lower than 1 month-old infants (P less than .05). To provide a time-averaged indication of blood glucose, glycosylated hemoglobin (GHb) measurements were made at 1 day, 1 week, 2 weeks, 1 month, 2 months, 1 year of age and in adults (greater than 3 years of age). GHb values ranged from 2.6% +/- 0.1 for 1 day old infants (n = 13) to 4.0 +/- 0.2 for adults (n = 10) with a steady increase during the first 2 months of life. Animals 1 year of age and younger had significantly lower glycosylated hemoglobin than adults. These studies indicate that blood glucose concentration is significantly lower in squirrel monkey neonates than in older infants, juveniles and adults. Maternal rejection, trauma, and associated problems occur commonly in socially reared squirrel monkeys. The marginal hypoglycemic state of these infants places them at high risk for clinical hypoglycemia as a sequel to such perturbations.     

Subject-specific profiles of QT/RR hysteresis

The time lag of the QT interval adaptation to heart rate changes (QT/RR hysteresis) was studied in 40 healthy subjects (18 females; mean age, 30.4+/-8.1 yr) with 3 separate daytime (>13 h) 12-lead electrocardiograms (ECG) in each subject. In each recording, 330 individual 10-s ECG segments were measured, including 100 segments preceded by 2 min of heart rate varying greater than +/-2 beats/min. Other segments were preceded by a stable heart rate. In segments preceded by variable rate, QT/RR hysteresis was characterized by lambda parameters of the exponential decay models. The intrasubject SDs of lambda values were compared with the intersubject SD of the individual means. The lambda values were also correlated to individually optimized parameters of heart rate correction. Intrasubject SDs of lambda were substantially smaller than the population SD of individual means (0.390+/-0.197 vs. 0.711, P<0.0001). The lambda values were unrelated to the QT/RR correction parameters. When compared with the corrected QT (QTc) for averaged RR intervals in 10-s ECGs and with the averaged RR intervals in 2-min history, QTc for QT/RR hysteresis led to a substantially smaller SD of QTc values (11.4+/-2.00, 6.33+/-1.31, and 4.66+/-0.85 ms, respectively, P<0.0001). Thus the speed with which the QT interval adapts to heart rate changes is highly individual with intrasubject stability and intersubject variability. QT/RR hysteresis is independent of the static QT/RR relationship and should be considered as a separate physiological process. The combination of individual heart rate correction with individual hysteresis correction of the QT interval is likely to lead to substantial improvements of cardiac repolarization studies.     

Electrocardiographic patterns in biventricular pacing delivered by second-generation cardiac resynchronization devices

Background

With increasing use of cardiac resynchronization therapy (CRT), treating physicians should be familiar with different electrocardiographic (ECG) patterns of left ventricular (LV) lead and biventricular (BiV) pacing. However, there are a few publications on ECG patterns during BiV pacing.

Electrocardiogram,vectocardiogram and body surface maps in patients with panic disorder

An increased risk of myocardial ischemic changes was demonstrated in patients suffering from panic disorder (PD). Using classical ECG methods, this risk cannot be evaluated in most patients. We measured the vectocardiogram (VCG) using Frank orthogonal leads and body surface maps (BSM) including 12-lead ECG. In our study of 11 PD patients (2 men, 9 women), without any seizures and pharmacological treatment and without cardiovascular symptoms, we found marked sinus tachycardia (heart rate 90.1 +/- 12.2 min(-1)) and a shorter R-R interval (678 +/- 93.6 ms) than in 27 controls (heart rate 73.6 +/- 7.7min(-1), R-R 822.7 +/- 86.4 ms) (5 men, 22 women) (p<0.001). The VCG measured spatial QRS-STT angle was more opened (70.3 +/- 24.5 degrees) than in the control group (49.5 +/- 19.5 degrees) (p<0.05). The maximum (extremum) in depolarization (DIAM max 30, 40) and repolarization (RIAM max 35) of body surface isoarea and isointegral (RIIM max) maps was less positive (p<0.001) and the minimum (DIAM min 40) was less negative than in the controls (p<0.05) even in the period free of a panic attack. Our results showed the changes in the heart electric field parameters occurred in PD patients when compared to the control group.     

Myocardial ischaemia in patients with frequent angina pectoris.

One hundred patients with angina pectoris underwent 16-point electrocardiographic (ECG) mapping of the left hemithorax during a standardised exercise test. Forty-five patients had maximum ST-segment depression at position V5, while 35 had no ECG signs of ischaemia at this position. In 20 V5 was on the edge of the precordial area, which showed less severe ST-depression than the central positions. An Oxford ECG recorder and highspeed analyser were modified and used in 50 of the patients with daily angina for recording ST-segment changes over 24 hours. Serial 24-hour ambulatory recordings from the edge of the precordial area of ischaemia identified during exercise detected a mean of only 14 +/- SD 3% of the episodes of ST-segment changes recorded from the centre of the same area. Only 16 +/- 2% of the episodes detected by ECG were accompanied by chest pain. More episodes occurred between 4 am and 6 am than at any other time during the night. This study shows the importance of recording ECG evidence of ischaemia from the precordial position showing maximum changes during exercise. ECG evidence of ischaemia occurs more frequently than anginal pain. These objective measurements add important information to the frequency of chest pain reported by patients with ischaemic heart disease.     

Echocardiographic assessment of age-associated changes in systolic and diastolic function of the female F344 rat heart.

Aging is associated with hypertrophy, dilatation, and fibrosis of the left ventricle (LV) of the heart. Advances in echocardiographic assessment have made it possible to follow changes in cardiac function in a serial, noninvasive manner. The purpose was to determine whether there is echocardiographic evidence of age-associated changes in chamber dimensions and systolic and diastolic properties of the female Fischer 344 (F344) rat heart. On the basis of previous invasive studies, it was predicted that echocardiographic assessment would detect age-associated changes in indexes of systolic and diastolic function. Rats were sedated with 1.5% isoflurane and placed in the supine position. Two-dimensional images and two-dimensionally guided M-mode, Doppler M mode, Doppler tissue, and pulsed-wave Doppler recordings were obtained from the parasternal long axis, parasternal short axis, and/or apical four-chamber views as per convention by using a 15-MHz linear array or 8-MHz phased-array transducer or a GE S10-MHz phased-array transducer. Compared with young adult 4-mo-old rats, there is a significant decrement in the resting systolic function of the LV in 30-mo-old female F344 rats as evidenced by declines in LV ejection fraction (80 +/- 9 vs. 89 +/- 5%; mean +/- SD), fractional shortening (43 +/- 9 vs. 54 +/- 8%) and velocity of circumferential fiber shortening (2.43 +/- 0.53 vs. 2.99 +/- 0.50 circ/s). Evidence for age-associated differences in diastolic function included an increase in isovolumic relaxation time (25.0 +/- 7.6 vs. 17.2 +/- 4.4 ms) and decreases in the tissue Doppler peak E waves at the septal annulus and at the lateral annulus of the mitral valve. The modest changes in systolic and diastolic LV function that occur with advancing age in the female F344 rat are likely to reduce the capacity of the heart to respond to hemodynamic challenges.     

Effect of temperature on heart rate in diploid and triploid brook charr, Salvelinus fontinalis, embryos and larvae

Increased cell size in triploid fish likely affects rates of respiratory gas exchange. Respiratory deficiencies can be addressed in fish by adjustments in cardiac output, through changes in heart rate and stroke volume. The aim of this study was to determine whether heart rate differs between triploid and control (diploid) brook charr, Salvelinus fontinalis, at embryo-larval stages, when the heart is easily visible and the fish are relatively inactive. Heart rate was measured at 6, 9 and 12 degrees C at three developmental stages: eyed-egg, hatch and yolk absorption. Heart rate was unaffected by ploidy, but increased with temperature and age from a low of 43.4+/-2.2 beats/min (6 degrees C, eyed egg) to a high of 73.3+/-1.5 beats/min (12 degrees C, yolk absorption). The Q(10) for heart rate was unaffected by ploidy and age, but decreased with temperature from 1.99+/-0.28 at 6-9 degrees C to 1.72+/-0.17 at 9-12 degrees C. Triploid brook charr thus do not use adjustments in heart rate as a mechanism to deal with the physiological consequences of altered haematology at embryo-larval stages.     

Accelerometer-based body-position sensing for ambulatory electrocardiographic monitoring

Our objective is to validate the ability of 3 appropriately placed accelerometers to determine body position during ambulatory electrocardiographic (ECG) monitoring and to demonstrate the clinical applicability of this method. During ambulatory (Holter) monitoring, the ability to know a patient's position (lying down, sitting, standing, or changing from one position to another) is important in the evaluation of common symptoms such as dizziness, palpitations, and syncope. Changes in body position are also known to alter the electrical axis of the heart, resulting in artifactual changes in QRS amplitude and ST-segment morphology. We have developed an ambulatory patient-monitoring instrument that, through the use of microfabricated accelerometers, can simultaneously record body-position information and 2 channels of ECG data. The accelerometers measure the effects of gravity and dynamic acceleration, allowing determination of a patient's orientation and movements. The accelerometer and ECG signals are input to a portable recorder and are filtered and digitized. Algorithms were developed to automatically determine body position. Ten healthy volunteers wore the device for 1 hour and followed a protocol of standing, sitting, walking, lying supine, and lying in the left and right lateral decubitus positions. An observer manually recorded times of position changes. Data were recorded and analyzed using software designed with MATLAB. The ability of the accelerometers and computer algorithms to determine body position was analyzed in terms of the sensitivity and specificity for each body position. The sensitivities for sitting, standing, walking, lying supine, lying right, and lying left were 98.8%, 99.2%, 95.5%, 99.1%, 98.9%, and 94.8%, respectively. The specificities were 99.7%, 99.4%, 99.6%, 99.0%, 99.8%, and 99.9%, respectively. The use of microfabricated accelerometers is a clinically feasible method to determine body position and can be applied to future studies correlating body position with ECG or other physiologic data.     

The development of homeothermy in mink (Mustela vison)

In mink (Mustela vison) kits newborn mortality is very high. One of the major causes of death is hypothermia. The objectives of this study were to observe the development of thermoregulation in mink kits, and their ability to maintain their body temperature during the postnatal period (1-50 days of age). Based on the kit's body weight (BW), and rectal and ambient temperature measurements during cold (+4 degrees C) and warm (+40 degrees C) exposures, a homeothermy index (HI) and cooling and warming rates were calculated. No significant differences in the body temperatures were found between the kits and the dam after 36 days of age. The kits were able to maintain homeothermy by 22 days of age (HI 90%). The body cooling rate was 0.88+/-0.04 degrees C min(-1) on day 1 but only 0.35+/-0.03 degrees C min(-1) at 22 days of age. The body WR was lower: day 1, 0.85+/-0.04 degrees C min(-1) and 0.22+/-0.03 degrees C min(-1) at 22 days of age. All measured and calculated thermophysiological variables were significantly influenced by BW and age of the kit.     

Early changes in rat hearts with developing pulmonary arterial hypertension can be detected with three-dimensional electrocardiography

The study aim was to assess three-dimensional electrocardiogram (ECG) changes during development of pulmonary arterial hypertension (PAH). PAH was induced in male Wistar rats (n = 23) using monocrotaline (MCT; 40 mg/kg sc). Untreated healthy rats served as controls (n = 5). ECGs were recorded with an orthogonal three-lead system on days 0, 14, and 25 and analyzed with dedicated computer software. In addition, left ventricular (LV)-to-right ventricular (RV) fractional shortening ratio was determined using echocardiography. Invasively measured RV systolic pressure was 49 (SD 10) mmHg on day 14 and 64 (SD 10) mmHg on day 25 vs. 25 (SD 2) mmHg in controls (both P < 0.001). Baseline ECGs of controls and MCT rats were similar, and ECGs of controls did not change over time. In MCT rats, ECG changes were already present on day 14 but more explicit on day 25: increased RV electromotive forces decreased mean QRS-vector magnitude and changed QRS-axis orientation. Important changes in action potential duration distribution and repolarization sequence were reflected by a decreased spatial ventricular gradient magnitude and increased QRS-T spatial angle. On day 25, LV-to-RV fractional shortening ratio was increased, and RV hypertrophy was found, but not on day 14. In conclusion, developing PAH is characterized by early ECG changes preceding RV hypertrophy, whereas severe PAH is marked by profound ECG changes associated with anatomical and functional changes in the RV. Three-dimensional ECG analysis appears to be very sensitive to early changes in RV afterload.     

Influences of calorie restriction and age on energy expenditure in the rhesus monkey

Caloric restriction (CR) is known to retard the aging process, and a marker of aging is decreased energy expenditure (EE). To assess longitudinal effects of CR on EE in rhesus monkeys (Macaca mulatta), data from 41 males (M) and 26 females (F) subjected to 9 or 15 yr of CR were studied. EE and body composition of monkeys 11-28 yr of age were measured using indirect calorimetry and dual X-ray absorptiometry. Total EE (24-h EE) was divided into daytime (day EE), nighttime (night EE), and daytime minus nighttime (D - N EE). M calorie-restricted monkeys showed a lower 24-h EE (means +/- SD = 568 +/- 96 kcal/day, P < 0.0001) than controls (C; 630 +/- 129 kcal/day). Calorie-restricted M had a lower night EE (difference = 36 kcal P < 0.0001) compared with C M, but after adjusting for FFM and FM, night EE was not different between calorie-restricted and C males (P = 0.72). The 24-h EE decreased with age (13 kcal decrease/yr, P < 0.0001), but there was no difference between CR and C. Adjusted for FFM and FM, D - N EE decreased with age (9 kcal/yr, P < 0.0001), with no interaction with age (P = 0.72). The F were compared with age-matched M selected from the male cohort. F had a lower 24-h EE (496 +/- 84 kcal/day) than M (636 +/- 139 kcal/day) (P < 0.0001). Adjusting for FFM and FM, night EE was lower in F compared with M (difference = 18 kcal, P = 0.077). Night EE did not differ between calorie-restricted and C younger monkeys after adjusting for FFM and FM. In conclusion, CR did not alter the age-related decrease in EE with CR.