Analysis of the position of the left ventricular apex and base during systole

Interregional electro-mechanical heterogeneity in the rabbit myocardium

BACKGROUND

Increased electrical heterogeneity has been causatively linked to arrhythmic disorders, yet the knowledge about physiological heterogeneity remains incomplete. This study investigates regional electro-mechanical heterogeneities in rabbits, one of the key animal models for arrhythmic disorders.

METHODS AND FINDINGS

7 wild-type rabbits were examined by phase-contrast magnetic resonance imaging in vivo to assess cardiac wall movement velocities. Using a novel data-processing algorithm regional contraction-like profiles were calculated. Contraction started earlier and was longer in left ventricular (LV) apex than base. Patch clamp recordings showed longer action potentials (AP) in LV apex compared to the base of LV, septum, and right ventricle. Western blots of cardiac ion channels and calcium handling proteins showed lower expression of Cav1.2, KvLQT1, Kv1.4, NCX and Phospholamban in LV apex vs. base. A single-cell in silico model integrating the quantitative regional differences in ion channels reproduced a longer contraction and longer AP in apex vs. base.

CONCLUSIONS

Apico-basal electro-mechanical heterogeneity is physiologically present in the healthy rabbit heart. An apico-basal electro-mechanical gradient exists with longer APD and contraction duration in the apex and associated regionally heterogeneous expression of five key proteins. This pattern of apical mechanical dominance probably serves to increase pumping efficiency.

Left ventricular apical thinning as normal anatomy

OBJECTIVE

Apical thinning of the left ventricular myocardium has been described by anatomists as a normal feature. Nonetheless, it does not appear in most anatomic atlases. We investigated its presence in healthy patients and patients with left ventricular hypertrophy using coronary computed tomographic arteriography (CCTA).

METHODS

Sixty-four patients without a history of cardiac disease and 8 patients with left ventricular hypertrophy were imaged using coronary computed tomographic arteriography.

RESULTS

All 64 patients had a focus of myocardial thinning at the left ventricular apex (mean, 1.2 mm [SD, 1.1 mm]). Its average span in the oblique coronal plane was 4.4 mm (2.9 mm), corresponding to a median area of 14.3 mm2 with an interquartile range of 3.9 to 31.6. The focus faced 4.8 degrees (5.9 degrees) toward the diaphragmatic side of the apex. The 8 hypertrophied hearts also had a zone of apical thinning. In a subset of 12 patients in whom functional data were analyzed, this focus did not thicken or move over the cardiac cycle.

CONCLUSIONS

A zone of substantial thinning of the left ventricular apex is a normal anatomic feature.

Assessment of right ventricular function with Doppler echocardiographic indices derived from tricuspid annular motion: comparison with radionuclide angiography

OBJECTIVE

To assess right ventricular systolic function using indices derived from tricuspid annular motion, and to compare the results with right ventricular ejection fraction (RVEF) calculated from radionuclide angiography.

DESIGN

Pulsed Doppler echocardiography indices were obtained from 10 patients with a normal RVEF (group 1) and from 20 patients whose RVEF was less than 45% (group 2).

RESULTS

The patients in the two groups were similar in age, systolic blood pressure, and heart rate. There was a close correlation between the tricuspid annular motion derived indices (D wave integral (DWI), peak velocity of D wave (PVDW), and tricuspid plane systolic excursion (TPSE)) and RVEF (r = 0.72, 0.82, and 0.79, respectively). DWI was significantly higher in group 1 than in group 2. PVDW discriminated adequately between individuals with abnormal and normal right ventricular ejection fraction. The sensitivity and specificity of tricuspid annular motion derived indices were very good.

CONCLUSIONS

Indices derived from tricuspid annular motion appear to be important tools for assessing right ventricular systolic function.

Myocardial revascularization in patients with ischemic cardiomyopathy: functional observations

OBJECTIVE

A prospective angiographic study was undertaken to investigate, with an objective analysis, the global and regional wall response to myocardial revascularization.

METHODS

Thirty-one patients (30 men and 1 woman, mean age, 61 years) with a left ventricular ejection fraction of less than 0.30 were admitted to our institution between 1992 and 1995 for two- or three-vessel coronary artery disease requiring myocardial revascularization. All patients underwent isolated coronary artery bypass grafting and were studied 3 months later with angiography. Preoperative and postoperative wall motion were analyzed using special software that computed a segmental left ventricular ejection fraction, generating a segmental score. Computerized analysis allowed us to distinguish patients with diffuse hypokinesis and a symmetric contraction pattern from patients with akinesis involving at least two segments and an asymmetric contraction pattern.

RESULTS

There were no operative deaths and no patient required intraaortic balloon counterpulsation. One patient had postoperative enzymatic evidence of myocardial infarction. Postoperative angiography showed a graft patency rate of 84%. Global analysis showed a small but significant rise in the left ventricular ejection fraction (0.25 +/- 0.51 to 0.31 +/- 0.70, p < 0.001) and a fall in the left ventricular end-diastolic pressure (23.7 +/- 10 to 16.5 +/- 9 mm Hg, p < 0.01). Mean scores always have been lower after the operation than before it, with the best results obtained for the apex and the worst for the anterobasal segment. The group with a symmetric contraction pattern showed a trend toward a better hemodynamic response than the group with an asymmetric contraction pattern. Regression analysis revealed two important predictors of segmental functional improvement: (1) the absence of an echocardiographic scar, and (2) the presence of a collateral circulation.

CONCLUSIONS

Coronary artery bypass grafting produced a small but substantial improvement in patients with ischemic cardiomyopathy. The greater benefit occurred in patients with a symmetric contraction pattern. The absence of an echocardiographic scar and the presence of a collateral circulation predicted segmental functional improvement.

The apical ventricular lesion in Chagas' heart disease

Apical lesions of the left ventricle, ranging from endocardial thickening to aneurysms, are commonly found in Chagas' heart disease. These abnormalities can be identified by ventriculography, two-dimensional echocardiography and radioisotopic studies. Generally, clinical manifestations are limited to arrhythmias and thromboembolic. The lesions are usually small and apparently do not play a role in ventricular dysfunction.

Quantitative regional contraction analysis of cineventriculography: reporting, filing, and retrieval functions using a personal computer

A new method for the semiobjective evaluation of left ventricular wall contraction is proposed that uses a percent reduction of areas. The calculation model uses orthogonal coordinates, an internal reference system, and the concept of nonuniform reduction of the cavity, with its obliteration at the apex. From a normal patient population (ten males, four females; aged 45 +/- 13 years), a "normal reference curve" of contraction was obtained. A second patient group (56 males, two females, aged 56 +/- 7 years) with definite contraction abnormalities was then analyzed. A third group (eight males, one female, aged 56 +/- 10 years) was studied before and after nifedipine administration (1 mg over 2 min IV). Specific algorithms compare individual patient contraction curves with the normal reference curve and compute the score point system of contraction analysis. Data are automatically codified and filed during introduction. This saves time and allows a rapid retrieval of data grouped under different coded features. These features include the location and type of wall contraction abnormalities. This method of reading ventriculograms has been shown to be in accordance with the diagnosis of experienced observers and can detect small contraction changes that are induced pharmacologically. The method is proposed as a valuable tool for semiobjective evaluation of left ventricle wall contraction and to facilitate data collection in multicenter collaborative studies.