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PubMedDate not supplied

Spectral analysis of heart period variance (HPV)--a tool to stratify risk following myocardial infarction.

The purpose of this study was to contribute to the improvement of stratification of post-myocardial infarction patients at increased risk of malignant ventricular arrhythmia (MVA). Power spectral analysis of heart period variability (HPV) was used as a non-invasive tool to assess cardiac autonomic control. Three groups were used: (1) post-myocardial infarction patients with MVA; (2) post-myocardial infarction patients without MVA; and (3) a control group without heart disease. Spectral analysis of HPV (AR model) was performed on four minute long RR-interval time series derived from consecutive hours of Holter ECG. Significant decrease of powers of mid-frequency (MF) (70-150 mHz) and high-frequency (HF) (150-450 mHz) spectral components of HPV was obtained in Group 1 as compared to Group 2 (p = 0.001 and p = 0.02, respectively). There were no significant differences between groups concerning the power of low frequency (LF) (10-70 mHz) component HPV, spectra of patients in Group 1 were dominated by a single low frequency spectral peak (with a central frequency of 37 mHz). The relative power was computed as the percentage of power in each of the above (HF, MF, LF) components related to the total spectral power. Highly significant differences (p = 0.04) were obtained between Group 1 and Group 2 concerning relative powers of MF and LF components as well as LF/MF ratio. The above method appeared to be highly sensitive in differentiating patients with increased risk of MVA.

Adult↗
PubMed1991

[Magnetocardiography. Biomagnetic localization of impulse development and transmission of the heart].

Magnetocardiography is a non-invasive biomagnetic technique for measuring magnetic fields produced at the surface of the body when the heart is stimulated to beat. The measurement is contact-free and is independent of tissue resistance. For the first time, magnetocardiography employing multi-channel systems permits the accurate, non-invasive localization of accessory conduction pathways and ectopic ventricular activity.

Cardiac Complexes, Premature↗
PubMed1982

Effect of nebulized isoproterenol on cardiac conduction in man.

The effects of Isuprel administered by means of a mistometer were studied in 8 patients with heart disease. Recordings were made at varied heart rates using atrial pacing. In addition, the functional and effective refractory periods were measured with the use of the extra stimulus technique. Four inhalations of the mistometer were administered to each patient (0.5 mg). The AH interval was 100 +/- 13 msec before and 93 +/- 23 msec 5 minutes after the Isuprel administration (p less than 0.05). Isuprel significantly reduced the AH interval with atrial pacing. The AH interval at an atrial pacing rate of 100/minute was 148 +/- 70 msec before and 131 +/- 51 msec after Isuprel (p less than 0.05). Isuprel had no significant effect on the HV interval. The effective and functional refractory period of the atrioventricular node was not significantly changed after Isuprel. The heart rate and blood pressure showed no significant change after Isuprel. No cardiac arrhythmias were seen. (The systemic absorption of the drug was probably minimal.) Isuprel administered by means of the mistometer can improve conduction through the atrioventricular node. Nevertheless, the potent bronchodilating effects of Isuprel and the absence of tachycardia and cardiac arrhythmias does attest to the safety of this agent.

Administration, Oral↗
PubMed1992

[Conventional roentgen functional diagnosis--videodensitometry. 4. Conventional roentgen videodensitometry exemplified with peri-cardiac vessels].

It is possible to record movement-parameters by means of roentgen videodensitometry of the great central vessels as well the pulmonary artery as the thoracic aorta visible in fluoroscopic image (provided by videorecorder). We could noninvasively measure pre-ejection periods (PEP) for the right heart (PEP f) as well for the left heart (PEP g) by synchronous electrocardiography for each cardiac action and for each examination process. It is important to form a quotient between PEP f and PEP g in the individual case. First findings in patients with cardiac septal defects (with and without right heart block and pulmonary hypertension) show characteristic quotients and figures of the curves. In cases with electrocardiographic left heart block the elongated PEP g can be stated in graduated form. Further investigations on the mechanic interaction between the right and left heart, especially in cases of disorders in the heart conduction system, might be of interest.

Absorptiometry, Photon↗
PubMed1982

Hyperbaric exposures alter cardiac excitation-contraction coupling.

Cardiac excitation-contraction (E-C) coupling variables were measured in anesthetized cats during helium-oxygen dives to 1000 fsw (305 msw). At constant pacing rates of 190-300/min the delay between onset of ventricular excitation and onset of developed pressure increased with depth, the larger increases occurring at faster rates. The electrocardiographic Q-T interval increased with depth at all rates, but rate-related shortening of Q-T was less at depth. At a rate of 190, the indexes of contractile performance were enhanced by increases in depth, but they showed little change or were lessened at faster rates. Predive changes in contractility, time to peak pressure, and systolic duration correlated positively with rate-induced changes in the Q-T interval. The correlations were reduced or reversed at depth, however, suggesting a dissociation of E-C coupling. Several cases of conduction arrhythmias or pulsus alternans were encountered with increases in depth and heart rate. These results suggest cardiac E-C coupling is altered by interactions of depth and heart rate. Further, these findings may have relevance to the capacity of the cardiovascular system to support periods of work in a hyperbaric environment.

Animals↗
PubMed1976

Electrocardiogram in Hyperkalemia: electrocardiographic pattern of anteroseptal myocardial infarction mimicked by hyperkalemia-induced disturbance of impulse conduction.

In a patient with renal failure and shortness of breath, Q waves transiently appeared in the right precordial leads of the electrocardiogram (ECG) during episodes of hyperkalemia, without a substantial change in mean electrical axis. With restoration of the plasma potassium level to normal, R waves reappeared in these leads. It is concluded that the transient development of Q waves in the right precordial leads during hyperkalemia resulted from a hyperkalemia-induced conduction disturbance. Hyperkalemia, by affecting conduction in Purkinje fibers of ventricular muscle, or both, disturbed the normal sequence of septal and anterior wall depolarization and resulted in an ECG pattern that mimicked that of anteroseptal myocardial infarction. Clinically, hyperkalemia-induced conduction disturbances of this type must be included in the differential diagnosis of the ECG that suggests an anteroseptal myocardial infarction.

Adult↗
PubMed1976

Effect of cold isotonic glucose infusion on A-V nodal conduction.

His bundle electrograms were performed in eight patients with organic heart disease. Recordings were made at various rates utilizing right atrial pacing. A solution of 100 cc of iced cold 5% glucose and water was infused through a cardiac catheter placed at the level of the tricuspid valve. The P-A, A-H, H-Q and H-S intervals were determined before and immediately after the cold water infusion. A significant prolongation of the A-H interval occurred with negligible effects on the P-A, H-Q and H-S intervals. At the atrial pacing rate of 100/min the average A-H interval increased from the control value of 116 to 125 msec after the infusion (P less than 0.02); at the pacing rate of 140/min, the A-H interval increased from 147 to 158 msec (P less than 0.01). This represents an impairment in conduction through the atrioventricular node.

Action Potentials↗
PubMed2006

Low-dose exercise training does not influence cardiac autonomic control in healthy sedentary men aged 55-75 years.

The purpose of this study was to evaluate the effects of a realistic, feasible, and commonly used fitness training programme on cardiac autonomic control in 14 sedentary men aged 62.0 +/- 6.1 years (mean +/- s). All participants performed a one-year fitness training programme in which training intensity and frequency were specifically chosen to be compliant for the majority of the participants (2-3 sessions per week at moderate intensity). At the same time, a reference group consisting of 15 sedentary age-matched men (age 64.2 +/- 6.5 years) did not change their habitual physical activity. Measurements were performed before and after the training intervention. Cardiac autonomic control was inferred from resting values (supine and standing) of heart rate variability (HRV) computed in the frequency domain over 10-min intervals. Endurance capacity was evaluated during a maximal incremental bicycle ergometer test. In spite of an increase in peak oxygen consumption (VO2peak) by 6.4% after training, heart rate in the training group remained unchanged at rest and at the same metabolic demand. No changes in resting parameters of HRV were shown for either groups or positions. Results from this study provide no evidence of a clinically meaningful increase in the vagal modulation to the sinus node at rest after one year of low-volume and moderate-intensity fitness training in men aged 55-75 years.

Aged↗
PubMed1999

Differential effects of aging on heart rate variability and blood pressure variability.

Previous studies investigating autonomic cardiovascular control in elderly persons usually included analysis of R-R interval but not of blood pressure variability. "Physiological" blood pressure rise during the aging process was not accounted for as a possible confounding factor. This study was designed to characterize the relationship between age and short-term heart rate (HR) and blood pressure (BP) variability, independently of the "physiological" rise in BP associated to aging. The study was carried out in 65 "normotensive" (BP< or =140/80 mm Hg) healthy subjects, ranging in age from 18 to 80 years. BP and HR were recorded at rest with a Finapres device. Low-frequency (LF = 0.066 to 0.129 Hz) and high-frequency (HF = respiratory peak +/-0.05 Hz) components of HR and BP variability were assessed using fast-Fourier spectral analysis. Transfer-function analysis between systolic BP and HR variability permitted the calculation of the gain of baroreflex sensitivity. Significant results of this study include a continuous and linear decline with age of normalized LF spectral power of HR in the standing position and of normalized HF spectral power of HR during paced breathing. No correlation was found between age and BP variability, except for LF diastolic BP spectral power in the standing position. The baroreflex gain was negatively correlated with age. The effect of aging on autonomic nervous system cardiac control is progressive and continuous throughout an 18-80 years age range. Although the aging process diminished HR variability and diastolic BP variability, it had no influence on systolic BP variability.

Adolescent↗
PubMed1986

Cardiovascular effects of and interaction between calcium blocking drugs and anesthetics in chronically instrumented dogs. II. Verapamil, enflurane, and isoflurane.

The effects of enflurane and isoflurane on the cardiovascular system and cellular calcium kinetics are somewhat different. Consequently, the interaction with the calcium channel blocking drug, verapamil, may also differ. In order to compare the anesthetics, the authors studied the effects of two infusion doses of verapamil (which produced plasma levels of 90 and 180 ng X ml-1) on cardiovascular dynamics and regional blood flow in awake dogs. On two other days, in the same dogs, the effects of approximately 1.1 and 2 MAC enflurane and isoflurane were first studied and then the same verapamil dose regimens while the same anesthetic concentrations were maintained. Verapamil produced only increases in heart rate and the P-R interval in the awake animal. The high dose of both anesthetics markedly decreased mean aortic pressure and left ventricular rate of tension development (dP/dt), and increased heart rate. However, only enflurane also decreased myocardial segment length shortening and increased left atrial pressure. Neither anesthetic alone affected coronary or renal blood flow, while both increased carotid blood flow at the low dose. Verapamil infusion during 1.2 MAC enflurane was more depressant than during 1.2 MAC isoflurane, but the combination of verapamil with 2 MAC concentration of both anesthetics was equally depressant. Both doses of both anesthetics increased plasma verapamil levels compared with the same verapamil dosing regimen awake. When these results are compared with those previously reported for halothane, the effects of verapamil during all three anesthetics are more similar than different.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Endotracheal↗
PubMed2005

Abnormalities of ventricular repolarization in mitral valve prolapse.

OBJECTIVES: Mitral valve prolapse (MVP) is associated with arrhythmias and sudden death. Some studies suggest that abnormalities of the autonomic nervous system (ANS) may contribute to these arrhythmias. In a family investigation with genetic analysis of patients carrying a MVP, we performed a Holter study to define the autonomic profile of MVP. METHODS AND RESULTS: A 24-hour digitized 3-lead Holter ECG was recorded in 30 patients with MVP and in two control groups, a group of 30 healthy relatives and a group of 31 healthy volunteers. We studied especially heart rate variability (HRV) and QT dynamicity. The slope of the relationship between ventricular repolarization and heart rate was studied separately during day and night. There was no difference in HRV (SDNN, rMSSD) among the three groups. On the contrary, QT interval duration was increased in patients with MVP as compared to healthy relatives (QT end: 409+/-52 ms vs 372+/-23 ms, P<0.05; QT apex: 319+/-42 ms vs 286+/-23 ms, P<0.01) and to healthy volunteers (QT end: 409+/-52 ms vs 376+/-25 ms, P=0.004; QT apex: 319+/-42 ms vs 289+/-23 ms, P<0.01). Nocturnal ventricular repolarization rate dependence was increased in MVP as compared to healthy relatives (0.16+/-0.06 vs 0.13+/-0.04, P<0.05) and to healthy volunteers (0.16+/-0.06 vs 0.11+/-0.06, P<0.001) whereas the 24-hour and diurnal QT-R-R slope was not disturbed. CONCLUSION: In MVP, QT is increased and the circadian modulation of QT end/RR slope is disturbed with an increased nocturnal rate dependence. These abnormalities of ventricular repolarization might explain the risk of arrhythmic events in MVP.

Autonomic Nervous System↗