Onset Of Mechanical Contraction Research Articles

Electromechanical decoupling with multisite onset of mechanical contraction in patients with different underlying heart diseases derived to gated-SPECT

Abstract Backgroud/Introduction Varying degrees of left ventricle (LV) mechanical dyssynchrony have been detected in some patients without electrical dyssynchrony. However, the site of onset of ventricular mechanical contraction as part of the electromechanical coupling process has not been fully described. Purpose To characterize LV contractile dynamics associated with multisite onset of mechanical contraction (OMC). Methods Phase histograms at rest were obtained in a sample of consecutive patients referred to 99mTc-MIBI gated-SPECT (radiotracer dose at rest: 925 MBq). Visual interpretation was performed through a semi-quantitative perfusion scale from 0 to 4 in a 17-segment model. Automated analysis included segmental summed rest, stress and difference scores (SRS, SSS and SDS), and also rest and post-stress functional parameters. Applying SyncTool from Emory Cardiac Toolbox® we obtained peak amplitude (PA), standard deviation (PSD) and phase bandwidth (PBW) indexes from resting phase histogram, detecting the site of OMC in LV. Then, we detected the patients with multisite (“multipoint”) OMC, defined as the onset in at least 3 of 17 segments. Latest site of mechanical contraction was recorded in last 10–30 degrees of phase. Histogram indexes were compared with a control group from our sample (n=24) and with controls reported by Chen J (n=90) by paired t test (p=0.05, two tailed). Results Multisite OMC was found in 19/137 patients (14%); affected from chronic coronary artery disease (n=13), hypertensive heart disease (n=2), inflammatory cardiomyopathy (n=1), hypertrophic cardiomyopathy (n=1) and nonischemic dilated cardiomyopathy (n=2). ECG showed left bundle branch block in one case and biventricular pacing in another. Multisite OMC was associated with diabetes (47.3%), lower LVEF (44.2±15.3%) and higher cavitary volumes (104.5±61.4 ml), SRS (17.0±10.7%) and incidence of fixed defects attributed to old infarct (77.8%); p<0.05 for all comparisons. Subjects with multisite OMC and chronic coronary disease (n=13) were 63±13 years old, 54% diabetic, LVEF=39.9±13.6%, telesystolic LV volume=112.4±64.9 ml, SRS=12.5% and SDS=4.2%. All patients with multisite OMC exhibited marked mechanical dyssynchrony at rest (PA=121.7±16.3, PSD=47.6±19.8, PBW=148.3±64.2 degrees (p<0.05 for the comparisons of PSD and PBW with sample controls and for the comparisons of all indexes with reported controls). In 4 of them (21%) a multisite late mechanical contraction was also detected. Conclusions Electromechanical decoupling with “multipoint” OMC is not infrequently found in patients referred to gated-SPECT, even in the absence of wide QRS complex. This subpopulation of patients is characterized by several functional high risk markers. Additional prognostic implications of this mechanical substrate, that seems to be common to several heart diseases, deserves further evaluation in large series subjected to prolonged clinical and physiological follow-up. Funding Acknowledgement Type of funding source: None

Electrical stimulation of cultured lepidopteran dorsal vessel tissue: an experiment for development of bioactuators

An insect dorsal vessel (DV) is well suited for a bioactuator since it is capable of contracting autonomously, and its tissue and cells are more environmentally robust under culturing conditions compared with mammalian tissue. In this study, electrical pulse stimulation was examined so as to regulate a bioactuator using the DV tissue. The DV tissue of a larva of Ctenoplusia agnate was assembled on a micropillar array, which was stimulated after culturing for about 3 wk. The contraction of the DV tissue was evaluated by image analysis to measure lateral displacements at the micropillar top. As a result, suitable stimulation conditions in a 35-mm petri dish were determined as: applied voltage of 10 V with 20-ms duration. Next, the time lag between the onset of electrical stimulus and the onset of mechanical contraction (electromechanical delay (EMD)) was estimated. A light-emitting diode (LED) was connected serially with the petri dish, and the LED flashed when electrical pulses were given. Movie images were analyzed in which electrical pulses made the DV tissue contract and the LED flashed virtually simultaneously; from these, the EMD was estimated as approximately 50 ms. These results suggest that the electrical pulse stimulation is capable of regulating the DV tissue, and the micropillar array is a useful biological tool to investigate physiological properties of muscle tissue.

Left Ventricular Mechanical Dyssynchrony as Assessed by Phase Analysis of ECG‐Gated SPECT Myocardial Perfusion Imaging

Cardiac resynchronization therapy (CRT) has shown benefits in patients with severe heart failure. The traditional criteria to select patients for CRT (NYHA class III or IV, depressed left ventricular (LV) ejection fraction, and prolonged QRS duration) result in at least 30% of the selected patients with no response to CRT. Recent studies with tissue Doppler imaging (TDI) have shown that the presence of LV dyssynchrony is an important predictor for response to CRT. Phase analysis has been developed to assess LV dyssynchrony from electrocardiography-gated single photon emission computed tomography (GSPECT) myocardial perfusion imaging (MPI). This technique uses Fourier harmonic functions to approximate regional wall thickening over the cardiac cycle and to calculate phases of regional onset of mechanical contraction (OMC). These OMC phases are obtained three-dimensionally over the left ventricle to generate an OMC phase distribution. Quantitative indices are calculated from the phase distribution to assess degree of LV dyssynchrony. This technique has been compared to other methods of measuring LV dyssynchrony and shown promising results in clinical evaluations. In this review, the phase analysis methodology is described and its up-to-date validations are summarized.

Onset of left ventricular mechanical contraction as determined by phase analysis of ECG-gated myocardial perfusion SPECT imaging: Development of a diagnostic tool for assessment of cardiac mechanical dyssynchrony

A count-based method using technetium-99m sestamibi electrocardiography-gated myocardial perfusion single photon emission computed tomography imaging has been developed to extract the left ventricular (LV) regional phase of contraction (onset of mechanical contraction [OMC]) throughout the cardiac cycle. This study was performed to develop OMC normal databases and dynamic OMC displays for assessment of cardiac mechanic dyssynchrony. LV regional phases were extracted from 90 enrolled normal subjects (45 men and 45 women) by use of the Emory Cardiac Toolbox and then submitted to statistical analysis to generate the normal databases. The LV OMC wave was dynamically propagated over the perfusion polar map by blackening either sequential phase bins or all past phases. The developed OMC normal databases consisted of peak phase (134.5 degrees +/- 14.3 degrees for men and 140.2 degrees +/- 14.9 degrees for women), phase SD (14.2 degrees +/- 5.1 degrees for men and 11.8 degrees +/- 5.2 degrees for women), and phase histogram bandwidth (38.7 degrees +/- 11.8 degrees for men and 30.6 degrees +/- 9.6 degrees for women), skewness (4.19 +/- 0.68 for men and 4.60 +/- 0.72 for women), and kurtosis (19.72 +/- 7.68 for men and 23.21 +/- 8.16 for women). Both statistical analysis and dynamic OMC displays were incorporated into a user interface as a diagnostic tool. The OMC normal databases and dynamic OMC displays should help clinicians evaluate cardiac mechanic dyssynchrony. Prospective clinical trials are needed to validate whether this tool can be used to select patients with severe heart failure symptoms who might benefit from cardiac resynchronization therapy.

Disorder in reciprocal innervation upon initiation of voluntary movement in patients with Parkinson's disease.

Reciprocal innervation of the soleus motoneurones upon initiation of voluntary ankle dorsiflexion was investigated in eight patients with Parkinson's disease. H-reflex and visually guided step tracking methods were used for testing motoneurone excitability and for controlling the timing of movement initiation, respectively. While reciprocal inhibition appeared almost simultaneously with the agonist electromyographic (EMG) onset in normal subjects (Kagamihara and Tanaka 1985), facilitation appeared in the majority of patients under the same onset condition. It increased slowly, reaching a maximum at about 100 ms after the EMG onset. It then subsided slowly at around 200-300 ms, and was replaced thereafter by an inhibitory effect. No coactivation of the soleus muscle was detected electromyographically. The facilitation between the EMG onset and the onset of mechanical contraction was attributed to the direct effect of the descending command from the brain, suggesting a certain disorder in controlling the system for reciprocal innervation.

Intramyocardial pressure in the canine heart: An experimental study

During 11 acute open-chest experiments with dogs, intramyocardial pressure was measured in the anterior wall of the left ventricle with a miniature pressure transducer mounted on a 1.6 mm diameter needle. Pressures were measured at the subendocardium (+/- 10 mm), midwall (+/- 7.5 mm), and subepicardium (+/- 5 mm). Simultaneous recordings of left ventricular pressure and two measures of intramyocardial pressure were made during control, acute volume overload, and after administration of verapamil. Maximal amplitude of the subendocardial pressure was higher and the maximal amplitude of the subepicardial pressure was lower than maximal left ventricular pressure for all interventions (p less than 0.001 and p less than 0.01). During volume overload left ventricular pressure increased more than intramyocardial pressure (left ventricular pressure 34%, subendocardial pressure 6%, midwall pressure 14%, and subepicardial pressure 14%). After the administration of verapamil intramyocardial pressure decreased more than left ventricular pressure (left ventricular pressure 16%, subendocardial pressure 26%, midwall pressure 13%, subepicardial pressure 32%). Positive and negative first derivatives of subendocardial pressure were higher than those of left ventricular pressure during control and after verapamil (between p less than 0.01 and p less than 0.001). Positive and negative first derivatives of subepicardial pressure were lower than those of left ventricular pressure during all interventions (p less than 0.001). The timing of the C-point (onset of mechanical contraction) and the positive first derivative of all tracings was synchronous within 8 msec in all interventions. The 0-point (crosspoint of the tangent to the diastolic plateau and the tangent to the relaxation slope; early diastole) of intramyocardial pressure came later than the 0-point of left ventricular pressure, indicating longer relaxation times in the myocardium (subendocardial pressure: control, p less than 0.001, volume, p less than 0.05, verapamil, no significance; midwall pressure: between p less than 0.05 and p less than 0.001; subepicardial pressure: between p less than 0.01 and p less than 0.001).