Electromechanical delay in the intact dog heart

Simultaneous Widefield Voltage and Dye-Free Optical Mapping Quantifies Electromechanical Waves in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Coupled electromechanical waves define a heart's function in health and diseases. Optical mapping of electrical waves using fluorescent labels offers mechanistic insights into cardiac conduction abnormalities. Dye-free/label-free mapping of mechanical waves presents an attractive non-invasive alternative. In this study, we developed a simultaneous widefield voltage and interferometric dye-free optical imaging methodology that was used as follows: (1) to validate dye-free optical mapping for quantification of cardiac wave properties in human iPSC-cardiomyocytes (CMs); (2) to demonstrate low-cost optical mapping of electromechanical waves in hiPSC-CMs using recent near-infrared (NIR) voltage sensors and orders of magnitude cheaper miniature industrial CMOS cameras; (3) to uncover previously underexplored frequency- and space-varying parameters of cardiac electromechanical waves in hiPSC-CMs. We find similarity in the frequency-dependent responses of electrical (NIR fluorescence-imaged) and mechanical (dye-free-imaged) waves, with the latter being more sensitive to faster rates and showing steeper restitution and earlier appearance of wavefront tortuosity. During regular pacing, the dye-free-imaged conduction velocity and electrical wave velocity are correlated; both modalities are sensitive to pharmacological uncoupling and dependent on gap-junctional protein (connexins) determinants of wave propagation. We uncover the strong frequency dependence of the electromechanical delay (EMD) locally and globally in hiPSC-CMs on a rigid substrate. The presented framework and results offer new means to track the functional responses of hiPSC-CMs inexpensively and non-invasively for counteracting heart disease and aiding cardiotoxicity testing and drug development.

Toward Ubiquitous Blood Pressure Monitoring via Pulse Transit Time: Theory and Practice

Ubiquitous blood pressure (BP) monitoring is needed to improve hypertension detection and control and is becoming feasible due to recent technological advances such as in wearable sensing. Pulse transit time (PTT) represents a well-known potential approach for ubiquitous BP monitoring. The goal of this review is to facilitate the achievement of reliable ubiquitous BP monitoring via PTT. We explain the conventional BP measurement methods and their limitations; present models to summarize the theory of the PTT-BP relationship; outline the approach while pinpointing the key challenges; overview the previous work toward putting the theory to practice; make suggestions for best practice and future research; and discuss realistic expectations for the approach.

Assessment of fetal atrioventricular time intervals by tissue Doppler and pulse Doppler echocardiography: normal values and correlation with fetal electrocardiography

OBJECTIVE

To establish gestational age-specific reference values of normal fetal atrioventricular (AV) time interval by spectral tissue Doppler imaging (TDI) and pulse-wave Doppler (PD) methods, and to assess their correlation with signal-averaged fetal PR intervals (ECG).

DESIGN

Cohort study.

SETTING

Tertiary centre for fetal cardiology. PATIENTS AND MEASURES: 131 pregnant women between 14 and 42 weeks' gestation underwent 196 fetal echocardiograms and 158 fetal ECG studies. TDI-derived AV intervals were measured as the intervals from atrial contraction (Aa) to isovolumic contraction (IV) and from Aa to ventricular systole (Sa) at the right ventricular free wall. PD-derived AV intervals were measured from simultaneous left ventricular inflow/outflow (in/out) and superior vena cava/aorta (V/AO) recordings.

RESULTS

Measurements were possible by ECG in 61%, by TDI in 100%, by in/out in 100% and by V/AO in 97% of examinations. Aa-IV correlated significantly better with PR intervals (y = 0.67x + 38.29, R(2) = 0.15, p < 0.0001, mean bias 8.0 ms) than did in/out (R(2) = 0.10, p = 0.002, bias 18.7 ms) and V/AO (R(2) = 0.06, p = 0.02, bias 12.4 ms). Gestational age and AV intervals were positively correlated with all imaging modalities (R(2) = 0.19-0.31, p < 0.0001).

CONCLUSION

This study showed the feasibility of fetal AV interval measurements by TDI, and established gestational age-specific reference data. TDI-derived Aa-IV intervals track ECG PR intervals more closely than PD-derived AV intervals and thus should be used as the ultrasound method of choice in assessing fetal AV conduction.

Doppler tissue imaging in the assessment of atrioventricular conduction time: validation of a novel technique and comparison with electrophysiologic and pulsed wave Doppler-derived equivalents in an animal model

Accurate assessment of atrioventricular conduction time (AVCT) is crucial for early detection of evolving fetal heart block. Simultaneous pulsed wave Doppler (PD) interrogation of left ventricular inflow and outflow is mainly used to study fetal AVCT. Limitations of this modality include its dependency on loading conditions and merging early and late diastolic inflow waves at faster heart rate (HR). Sequential analysis of atrioventricular myocardial motion by Doppler tissue imaging (DTI) might be more useful in this regard. In 15 open-chest pigs, AVCT was measured by PD, DTI, and electrocardiogram at baseline HR and during incremental atrial pacing up to 200 beats/min. Electromechanical delay and pre-ejection period were assessed at baseline and maximal HR. DTI-derived AVCT correlated better with PR intervals and allowed measurements at faster HRs than did PD (P < .05). Pre-ejection period prolonged with faster HR (P < .001), unlike electromechanical delay. In conclusion, DTI allows more accurate measurement of AVCT over a wider HR range than does PD.

Quantification of interventricular asynchrony during LBBB and ventricular pacing

The quantification of mechanical interventricular asynchrony (IVA) was investigated. In 12 dogs left bundle branch block (LBBB) was induced by radio frequency ablation. Left ventricular (LV) and right ventricular (RV) pressures were recorded before and after induction of LBBB and during LBBB + LV apex pacing at different atrioventricular (AV) delays. Four IVA measures were validated using computer simulations on experimentally obtained pressure signals. The most robust measure for IVA was the time delay between the upslope of the LV and RV pressure signals (DeltaT(up)), estimated by cross correlation. The induction of experimental LBBB decreased DeltaT(up) from -6.9 +/- 7.0 ms (RV before LV) to -33.9 +/- 7.6 ms (P < 0.05) in combination with a significant decrease of LV maximal first derivative of pressure development over time (dP/dt(max)). During LV apex pacing, DeltaT(up) increased with decreasing AV delay up to +20.9 +/- 14.6 ms (P < 0.05). Interventricular resynchronization (DeltaT(up) = 0 ms) significantly improved LV dP/dt(max) by 15.1 +/- 5.9%. QRS duration increased significantly after induction of LBBB but did not change during LV apex pacing. In conclusion, DeltaT(up) is a reliable measure of mechanical IVA, which adds valuable information concerning the nature of asynchronous activation of the ventricles.

The acute dose-related effects of ethanol on right ventricular function in anesthetized dogs

The acute dose-related effects of small to moderate doses of ethanol on right ventricular functioning were studied on 18 anesthetized, artificially ventilated dogs in 39 sessions. Diluted ethanol (from 25-37.5%) was infused during 40 minutes, yielding total doses of 1.0 g/kg (n = 15), and 1.5 g/kg (n = 12) with corresponding venous blood ethanol peak concentrations of 1.38 +/- 0.25 and 2.41 +/- 0.31 mg/ml, respectively. Heart rate increased up to 16% in groups receiving ethanol. In the control group receiving the equivalent volume of saline (n = 12) heart rate decreased 14%. Pulmonary arterial systolic pressure increased from 24 +/- 3 to 27 +/- 3 mmHg and diastolic pressure from 11 +/- 2 to 14 +/- 4 mmHg (p less than 0.05) when the ethanol dose was 1.0 g/kg. The pulmonary arterial resistance increased from 620 +/- 135 to 805 +/- 185 dyn.s.cm-5 (p less than 0.01). The peak dP/dt decreased maximally by 20% with increasing ethanol doses. Stroke volume decreased maximally by 14% but due to the increase in heart rate, cardiac output even increased. The changes in end-diastolic volume and pressure were not significant. Hence, the ethanol increased heart rate and afterload of the right ventricle but depressed the myocardium.

Left ventricular function in dogs 1 year after coarctectomy

Juxtaductal aortic coarctation was surgically created in beagle puppies at the age of 2 months and resected at the age of 10 months, after the development of good collateral circulation. Control dogs undergoing sham operations on each occasion were studied in the same environment. Cardiac catheterization was performed 1 year after the coarctectomy to evaluate the recovery of the heart. Cardiac output, heart rate, end-diastolic pressure, and Vmax were similar in both groups of seven dogs, but the systolic pressure gradient (SPG) over the operated area during isoproterenol infusion was significantly higher in the coarctectomized group, with a mean of 8.9 +/- 6.3 (SD) vs. 0.1 +/- 0.3 mmHg (p less than 0.05). The preejection period [PEP, 58 +/- 8 vs. 47 +/- 5 ms (p less than 0.01)], electromechanical delay [EMD, 18 +/- 3 vs. 13 +/- 3 ms (p less than 0.05)], and isometric contraction time [ICT, 39 +/- 7 vs. 32 +/- 4 ms (p less than 0.05)], were all significantly longer in the coarctation group after isoproterenol infusion. The results demonstrate that, even though cardiac output increased adequately during loading and mechanical pumping efficiency was preserved, excitation-contraction coupling was still prolonged. Thus, an anatomical successful coarctectomy, even at the age of 10 months, does not fully restore left ventricular function in dogs after chronic experimental coarctation.

Left ventricular responses to experimental aortic coarctation in growing puppies

The haemodynamic status of 8 coarctated and 7 sham-operated beagle puppies was studied by a catheterization technique at rest and during isoproterenol and volume loading at the ages of 7 (I) and 9 (II) months (5 and 7 months after the experimental coarctation). Proximal aortic systolic and pulse pressures were constantly higher in the coarctation group than in the control group (P less than 0.05), and the systolic pressure gradient across the coarctation was always significantly higher in the coarctation group [I at rest mean 45 +/- 5 (SD) vs 5 +/- 4 mmHg, P less than 0.001, and after I isoproterenol infusion 56 +/- 9 vs 10 +/- 6 mmHg, P less than 0.001, and after I dextran infusion 58 +/- 10 vs 8 +/- 7 mmHg, P less than 0.001]. The time constant of exponential isovolumic left ventricular pressure fall after the isoproterenol tests was longer in the coarctation group (I 28 +/- 8 ms and II, 30 +/- 4 ms) than in the control group (I, 21 +/- 2, P less than 0.05 and II, 19 +/- 3 ms, P less than 0.005), indicating impaired relaxation. The tension time index during the volume loading tests increased in the coarctation dogs (I, 4150 +/- 660 and II, 4080 +/- 810 mmHg s min-1) to higher levels than in the control group (I, 3550 +/- 220, II, 2540 +/- 1140 mmHg s min-1, P less than 0.05 both). Cardiac output, left ventricular end diastolic pressure, inotropic parameters and heart rate were similar in both groups during the infusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetate-induced changes in cardiac energy metabolism and hemodynamics in the rat

The hemodynamic and metabolic effects of acetate were studied in rats in vivo and in the isolated perfused heart. Hemodynamic parameters, myocardial phosphagens, inorganic phosphate, and adenosine were measured in vivo. Acetate uptake, coronary flow, O2 consumption, parameters of the cellular energy state, and hypoxanthine compounds and their washout were measured in heart perfusion experiments. Heart rate (HR), cardiac output, and the peak derivative of the left ventricular pressure rise (dP/dtmax) increased significantly during acetate infusion in vivo, but mean arterial pressure, systolic arterial pressure, and systemic vascular resistance decreased. Heart muscle ATP concentrations decreased after 7 min of acetate infusion. In vivo cardiac work load (HR.(peak left ventricular pressure] showed a positive correlation with tissue adenosine concentration and a negative correlation with phosphorylation potential. Acetate uptake in the perfused hearts was about 2.5 mumol/min per gram wet weight. Acetate perfusion increased O2 consumption and coronary flow concomitantly with a decrease in tissue ATP concentration. Tissue AMP and perfusate effluent adenosine concentration and adenosine output increased significantly, perfusate adenosine showing a non-linear positive correlation with coronary flow. The results demonstrate that acetate induces considerable changes in hemodynamics and metabolism in the heart.

The cardiovascular effects of deconditioning after endurance training in rats

The haemodynamic effects of endurance training and physical deconditioning were studied in anaesthetized rats using aortic and left ventricular pressure recordings and volume measurements by thermodilution method during isoproterenol and CaCl2 loads. The resting stroke volume was significantly larger in the training group (TG I, n = 10) than in the control group (CG I, n = 13). During the CaCl2 infusion stroke index, end-diastolic and end-systolic volumes increased in the TG I, but decreased in the CG I. Both isoproterenol and CaCl2 decreased systemic vascular resistance in the TG I, but increased it in the CG I. After a six-week deconditioning following training period (TG II, n = 10) stroke index, end-diastolic and end-systolic volumes decreased during CaCl2 and isoproterenol infusions similarly to the control deconditioning group (CG II, n = 12). These responses differed significantly from those observed in the TG I. Peripheral resistance increased in both the CG II and the TG II. Cardiac hypertrophy observed during training was partly reversed after the deconditioning period. In conclusion, endurance training improves the pumping performance of the rat heart by enhancing the diastolic filling of the left ventricle and decreasing peripheral resistance during inotropic load. Left ventricular contractility is not affected. A six-week deconditioning period after endurance training returns the haemodynamic changes to sedentary levels.

Anabolic steroids alter the haemodynamic effects of endurance training and deconditioning in rats

The haemodynamic effects of endurance training with or without anabolic steroid treatment (nandrolone decanoate, 5.0 mg kg-1 week-1) were studied before and after a six-week sedentary period in anaesthetized, open-chest rats during isoproterenol and CaCl2 loads. In comparison to the control group (CG I, n = 13) endurance training (TG I, n = 10) increased the resting stroke index significantly, end-diastolic pressure and during CaCl2 infusion the end-diastolic and end-systolic volumes. Peripheral resistance decreased in TG I during both inotropic loads but increased in CG I (P less than 0.01 between the groups). After combined endurance training and anabolic steroid treatment (TSG I, n = 16) the haemodynamic state was similar to that in CG I except peripheral resistance which was even higher than in CG I. The heart weight to body weight ratio was significantly greater both in TG I and TSG I than in CG I. After a six-week deconditioning period the haemodynamic values were essentially similar in endurance trained (TG II, n = 10) and in control rats (CG II, n = 12). After the sedentary period, in the simultaneously trained and anabolic steroid-treated group (TSG II, n = 13) stroke index and end-diastolic volume decreased more during isoproterenol load when compared with TG II or CG II (P less than 0.05 between the groups). Peripheral resistance was higher in the TSG II than in the two other groups. In conclusion, the enhanced pumping performance of the heart by increased left ventricular diastolic filling after endurance training is attenuated by simultaneous anabolic steroid treatment which further increases the peripheral resistance. Detraining reversed the main training effects in six weeks and simultaneous anabolic steroid treatment led to a decreased left ventricular filling and to elevated peripheral resistance after the sedentary period.

Reversibility of the haemodynamic effects of anabolic steroids in rats

The haemodynamic effects of 6 weeks nandrolone decanoate treatment (total dose 30 mg.kg-1) (SG I, n = 12) and their reversibility were studied in anaesthetised, open-chest male rats exposed to 5 min isoproterenol (2.5 micrograms.kg-1) and CaCl2 (25.0 mg.kg-1) loads. In SG I, the heart weight and its ratio to body weight were greater than in the untreated rats (CG I, n = 13) (p less than 0.05 and p less than 0.01 respectively). The initial heart rate and the inotropic and chronotropic responses to isoproterenol were lower in SG I than in CG I (p less than 0.05 in all cases). Peripheral resistance decreased during both infusions in SG I but remained unaltered in CG I (p less than 0.05). 6 weeks after finishing anabolic steroid treatment (SG II, n = 11), in the CaCl2-test the ejection fraction (p less than 0.05) and stroke index were smaller than in control rats of the same age (CG II, n = 12). Mean aortic pressure was lower in SG II than in CG II. In the CaCl2-test peripheral resistance was initially higher, but decreased during the infusion in SG II while it increased in CG II (p less than 0.05 in both cases). In conclusion, anabolic steroid treatment reversibly reduces the left ventricular response to isoproterenol. It decreases peripheral vascular tone during inotropic loads. Six weeks after the cessation of treatment, the pumping efficiency of the heart is reduced.

The effects of anabolic steroids and endurance training on systolic time intervals in the dog

The effects of administration of anabolic steroids (SG, n = 6), endurance training (EG, n = 7) and a combination of steroid administration (Methandienone R) and training (ESG, n = 7) on systolic time intervals (STI) in the dog heart were compared with control dogs (CG, n = 7) by a catheterization technique. Isoproterenol infusion was used as a positive inotropic load. Physical performance was checked with submaximal exercise test, a 30 beats min-1 decrease in heart rate response was considered a sufficient training effect. During isoproterenol infusion, exercise was found to enhance the pump performance of left ventricle and increased stroke volume was related to shortened pre-injection period (PEP) (P less than 0.05), whereas steroid administration failed to induce any significant differences in PEP or PEP/LVET (LVET = left ventricular ejection time) when compared with CG. However, when steroid administration was combined with endurance training, both PEP and PEP/LVET were lengthened significantly in comparison with EG (P less than 0.05 and P less than 0.01, respectively). In conclusion, it seems that the anabolic steroids affected the STIs only, when their administration was combined with endurance training.

The automatic computation of pressure-derived maximal shortening velocity (Vmax) of the unloaded contractile element in the intact canine heart left ventricle

Estimation of the maximum velocity (Vmax) of the contractile element of the intact left ventricular wall muscle demands extrapolation of the force-velocity curve to zero load. The present paper describes our on-line computation system for measuring and analysing pressure derived Vmax using both linear (Vmax-lin) and exponential (Vmax-exp) extrapolation methods. The developed pressure during isovolumetric phase of systole was used as an equivalent of the force. Testing on anaesthetized artificially ventilated dogs showed the exponential function to fit pressure-velocity data better than the straight line did. The Vmax-exp attained 15-35% greater values than Vmax-lin, but both responded almost equally when considered on the basis of linear regression analysis (r = 0.991, n = 725). Changes of contractility caused by i.v. infusion of isoproterenol, calcium chloride or propranolol were practically similar when assessed by either method of Vmax computation, or by dP/dtmax. Volume loading by dextran infusion increased not only dP/dtmax, by 33 +/- 13%, but also Vmax, up to 24 +/-. When arterial pressure was raised by phenylephrine infusion, or heart rate by atrial pacing, dP/dtmax increased significantly while Vmax remained unaltered. Hence, the linear and exponential dP/dtmax increased significantly while Vmax remained unaltered. Hence, the linear and exponential extrapolation procedures provided comparable values for Vmax, but the linear one due to its simplicity is more suited for on-line computation. The Vmax thus obtained is, however, not independent of the changes in preload.