The relation between left ventricular asynchrony, relaxation, outward wall motion and filling characteristics during control period and pacing-induced myocardial ischaemia in coronary artery disease

Pathophysiological Considerations concerning Uni- and Biventricular Mechanical Cardiac Assist

Mechanical assisted circulation by the means of cardiac assist devices is a routine procedure in modern cardiac surgery and cardiology. We investigated the impact of mechanical unloading on regional myocardial “stunning” and the influence of assisted circulation on left heart and right heart failure persevered by an ultimate addition of pulmonary hypertension in experimental set ups.

We found that mechanical unloading either during ischemia or in the early reperfusion phase attenuates stunning and enhances the return of synchronous heart performance.

In our global dysfunction model we showed that the right heart is dispensable. Sufficient inflow to the left heart is provided unless pulmonary hypertension is present. Also additional left heart support can not overcome the deleterious situation and in select cases only additional right heart support can prevent the “low LVAD output” syndrome.

We conclude that mechanical assisted circulation and mechanical unloading are beneficial in case of regional and global dysfunction persevered by pulmonary hypertension, however, the knowledge about interactions of assist systems and the circulation has to be improved in order to optimize clinical assist device performance.

Pacing-induced ST segment deviation in patients with unstable angina: clinical, angiographic, and hemodynamic correlation

To assess the clinical, coronary arteriographic, and hemodynamic differences between the unstable angina patients manifesting ST segment depression and those showing ST segment elevation as well as those demonstrating chest pain only without ST segment deviation during pacing, low-dose digital subtraction ventriculography was performed in 33 patients before and after abrupt cessation of atrial pacing during selective coronary arteriography. Transient ST segment depression during pacing was observed in 17 patients (52%), whereas 6 patients (18%) showed ST segment elevation; however, 10 patients (30%) did not manifest any ST segment deviation in spite of typical chest pain. Hypertension and a history of myocardial infarction were observed in a significantly higher (P < 0.05) proportion of patients with ST segment depression than in those with ST elevation. Patients who manifested ST segment depression during pacing had a higher incidence of triple-vessel disease (65 vs 17%; P < .05) as compared with the patients with ST segment elevation. Indirect evidence of intracoronary thrombi (complicated lesion, abrupt occlusion, and intraluminal filling defect) was noticed in a higher frequency (P < 0.05) in the group of patients with ST elevation during pacing. In patients with ST segment depression, no significant changes of global left ventricular (LV) functional parameters were observed. However, the length of the LV severe hypokinetic region was increased significantly (6.2 +/- 3.1 vs 23.5 +/- 6.2%; P < 0.005) during pacing in this group of patients. The shortening of the affected segments of the left ventricle was decreased significantly (52.3 +/- 3.6 vs 38.3 +/- 4.9%; P < 0.05) in these patients during pacing. In the group of patients with ST segment elevation during pacing, decrease in ejection fraction was associated with significant (P < 0.01) increase in midwall equatorial diastolic stress as compared with the patients with pacing-induced ST segment depression as well as patients without ST segment deviation. In the group of patients without ST segment deviation during pacing there was no considerable aggravation of LV global or regional function. This distinction should be taken into consideration in evaluating patients with unstable angina for diagnostic and therapeutic intervention.

Regional left ventricular mechanics in hypertrophic cardiomyopathy

BACKGROUND

Nonuniformity is a determinant of diastolic function. In patients with hypertrophic cardiomyopathy, hypertrophy, abnormal calcium handling, and regional ischemia can also play a role. This study was designed to assess regional mechanics, asynchrony, and asynergy in patients with hypertrophic cardiomyopathy.

METHODS AND RESULTS

Nine control subjects and 22 patients with hypertrophic cardiomyopathy were studied by biplane left ventriculography and high-fidelity pressure tracings for the assessment of diastolic function by computing the time constant of isovolumic relaxation, peak filling rate, and the constant of passive chamber stiffness. Regional mechanics were evaluated by dividing the left ventricle into six sectors in the right and left anterior oblique projections. Systolic and diastolic asynchrony were assessed from the coefficient of variation of the regional time intervals from end diastole to end systole and to peak filling rate, respectively. Asynergy was evaluated from the coefficient of variation of the regional area reduction. Regional passive elastic properties were estimated by computing the regional constant of chamber stiffness. In patients with hypertrophic cardiomyopathy, isovolumic relaxation was prolonged (time constant of isovolumic relaxation 101 +/- 41 versus 51 +/- 16 milliseconds in control subjects; P < .001) and the constant of chamber stiffness was increased (0.056 +/- 0.038 versus 0.025 +/- 0.010 mL-1; P < .001). Both systolic and diastolic asynchrony as well as asynergy were found. Regional mechanics showed hyperkinesia in the free wall, whereas the septum exhibited normal wall motion and increased constant of chamber stiffness.

CONCLUSIONS

Diastolic function is impaired in hypertrophic cardiomyopathy, and such an impairment is the consequence of nonuniformity and hypertrophy. The regions where the myopathic process is more pronounced show normal wall motion but increased stiffness. The inhomogeneity of regional wall motion with regional hyperkinesia and normokinesia of neighboring regions results in left ventricular asynergy.

Doppler assessment of right ventricular filling dynamics during volume loading in ischemic heart disease

To assess the effects of volume loading on right ventricular (RV) filling dynamics, the RV inflow pattern was recorded using pulsed Doppler echocardiography (PDE) during dextran infusion in 7 normal subjects (Group I) and 24 patients with ischemic heart disease. The patients with ischemic heart disease were divided into three groups according to the left ventricular (LV) and RV ejection fractions (EF). Group II consisted of 11 patients whose LVEF and RVEF exceeded 50%. Group III consisted of 7 patients whose LVEF was lower than 50% and RVEF was higher than 50%. Group IV was comprised of 6 patients whose LVEF and RVEF were lower than 50%. Peak flow velocity of the RV rapid filling wave in early diastole [R(T)] and that of the atrial contraction wave [A(T)] were measured, and the ratio of A(T) to R(T) [A(T)/R(T)] in each cardiac cycle was calculated. In some of the subjects, simultaneous right-sided cardiac catheterization was performed with a Swan-Ganz thermodilution catheter. The LV and RV function during volume loading were calculated according to the following formulae: delta Stroke volume index (SVI)/delta pulmonary artery wedge pressure (PAWP) and delta SVI/delta right atrial pressure (RAP), respectively. After dextran infusion, R(T) increased significantly in Groups I, II, and III, but not in Group IV. The A(T) and A(T)/R(T) ratio remained unchanged in all groups. The percent change of the R(T) correlated well with delta SVI/delta RAP (r = 0.56, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Single-beat estimation of the slope of the end-systolic pressure-volume relation in the human left ventricle

This study assessed a new method of estimating the slope (Ees) of the end-systolic pressure-volume relation (ESPVR) from a single beat of the human heart. Left ventricular pressure was recorded with a high-fidelity micromanometer in patients with heart disease during left ventriculography. Peak isovolumic pressure at the end-disastolic volume was estimated by a curve-fitting technique from an isovolumic left ventricular pressure curve. The ESPVR line was drawn from the estimated peak isovolumic pressure-volume point tangential to the left upper corner of the pressure-volume loop. The slope of this estimated ESPVR line from single-beat analysis was compared with the slope of the ESPVR line obtained from three pressure-volume loops in 16 patients given angiotensin II or nitroglycerin infusion. The estimated Ees was 5.0 +/- 2.2 mm Hg/ml/m2, and the conventional Ees was 4.9 +/- 2.7 mm Hg/ml/m2. The estimated Ees showed a positive correlation with the conventional Ees (r = 0.91, p less than 0.001, SEE = 1.2 mm Hg/ml/m2). In the other 13 patients, after dobutamine infusion (5 micrograms/kg/min i.v.) the estimated Ees increased significantly from 5.6 +/- 1.4 to 7.4 +/- 2.0 mm Hg/ml/m2 (p less than 0.01). Thus, the estimated Ees approximated the conventional Ees and was sensitive to a positive inotropic intervention. We conclude that this single-beat analysis method facilitates assessment of the beat-by-beat ESPVR of the human heart.

Improvement of left ventricular contraction and relaxation synchronism after recanalization of chronic total coronary occlusion by angioplasty

Twenty patients with a chronic total coronary artery occlusion were studied before and 1 to 48 months (mean 9) after successful recanalization by angioplasty and compared with a group of 20 normal subjects. Before angioplasty, 19 of these 20 patients had angina. Collateral vessels to the distal part of the occluded vessel were visible in all 20 patients. A previous myocardial infarction was documented in 14 patients (9 with a Q wave and 5 with a non-Q wave infarction). At the time of follow-up, three patients were symptomatic: one had unstable angina and two had a positive stress test. The follow-up angiogram showed a significant restenosis in six patients and reocclusion in two. The mean ejection fraction had improved slightly from 59 +/- 11% to 63 +/- 9% (p less than 0.05). Left ventricular wall motion synchronism was studied using two variables for 128 shortening segments: the "time of peak contraction" and the "time of peak relaxation," as obtained from biharmonic Fourier transformation for each segment. Their respective standard deviations reflect the synchronism of contraction and relaxation. The mean standard deviations of the two variables expressed in degrees of one cardiac cycle (360 degrees) were respectively: 5.5 +/- 0.4 degrees for the time of peak contraction and 6.0 +/- 0.5 degrees for the time of peak relaxation in the 20 normal subjects, 11.7 +/- 1.7 degrees and 23.0 +/- 3.0 degrees before recanalization and 9.6 +/- 1.8 degrees and 12.5 +/- 2.2 degrees at follow-up in the group of 20 patients. These values were significantly higher (p less than 0.05) in the patients than in the normal group.(ABSTRACT TRUNCATED AT 250 WORDS)