Causal relation between the pressure gradient and left ventricular ejection time in hypertrophic cardiomyopathy

The mitral valve in hypertrophic cardiomyopathy: old versus new concepts

Elongation and pathological thickening of the mitral valve (MV) is commonly seen in hypertrophic cardiomyopathy (HCM), and its pathogenic basis is poorly understood. Associated features include mal-positioning of the papillary muscles and MV, as well as systolic anterior motion (SAM) of the MV leaflets, which can worsen the turbulence and dynamic left ventricular outflow tract (LVOT) gradient. Coaptation of the MV leaflets depends on both anterior and posterior leaflet length and position, and failure of either to optimally adapt in this setting can result in mitral regurgitation or worsened LVOT obstruction. The cause of MV enlargement in HCM is not currently understood, and several different hypotheses may be relevant. The lack of correlation between MV size and the severity of left ventricular hypertrophy, as well as the early findings in genetically predisposed individuals with sarcomere mutations, suggest that it may be an intrinsic aspect of HCM in certain individuals. Other evidence points to a reactive process in the setting of excess production of paracrine growth factors in diseased myocardium that may influence valve overgrowth. Improved understanding of the responsible adaptive mechanisms will pave the way for studies targeted on the prevention and treatment of MV disease in HCM.

The 50-year history, controversy, and clinical implications of left ventricular outflow tract obstruction in hypertrophic cardiomyopathy from idiopathic hypertrophic subaortic stenosis to hypertrophic cardiomyopathy: from idiopathic hypertrophic subaortic stenosis to hypertrophic cardiomyopathy

Dynamic obstruction to left ventricular (LV) outflow was recognized from the earliest (50 years ago) clinical descriptions of hypertrophic cardiomyopathy (HCM) and has proved to be a complex phenomenon unique in many respects, as well as arguably the most visible and well-known pathophysiologic component of this heterogeneous disease. Over the past 5 decades, the clinical significance attributable to dynamic LV outflow tract gradients in HCM has triggered a periodic and instructive debate. Nevertheless, only recently has evidence emerged from observational analyses in large patient cohorts that unequivocally supports subaortic pressure gradients (and obstruction) both as true impedance to LV outflow and independent determinants of disabling exertional symptoms and cardiovascular mortality. Furthermore, abolition of subaortic gradients by surgical myectomy (or percutaneous alcohol septal ablation) results in profound and consistent symptomatic benefit and restoration of quality of life, with myectomy providing a long-term survival similar to that observed in the general population. These findings resolve the long-festering controversy over the existence of obstruction in HCM and whether outflow gradients are clinically important elements of this complex disease. These data also underscore the important principle, particularly relevant to clinical practice, that heart failure due to LV outflow obstruction in HCM is mechanically reversible and amenable to invasive septal reduction therapy. Finally, the recent observation that the vast majority of patients with HCM have the propensity to develop outflow obstruction (either at rest or with exercise) underscores a return to the characterization of HCM in 1960 as a predominantly obstructive disease.

Effects of exercise on the duration of diastole and on interventricular phase differences in patients with hypertrophic cardiomyopathy: relationship to cardiac output reserve

BACKGROUND

Our study sought to characterize the effect of exercise on the duration of left ventricular (LV) diastole and interventricular dyssynchrony in patients with hypertrophic cardiomyopathy (HCM). We hypothesized that an abnormally shortened diastolic time may adversely affect cardiac performance.

METHODS

We studied 49 symptomatic patients with HCM during incremental exercise. Twenty-nine patients had obstructive disease (HOCM) and 20 no resting or provocable gradient (HNCM). Right heart catheterization and high temporal resolution radionuclide angiography were simultaneously performed. The loss of diastolic time per beat (LDT(RR)) was quantified using a regression equation obtained from a healthy control group (n = 30).

RESULTS

During rest and peak exercise, a significant shortening of the relative duration of LV diastole (35.6 +/- 5 vs. 38.0 +/- 3 s/min and 29.3 +/- 6 vs. 32.4 +/- 3 s/min; P < or = .02) and an increased interventricular phase delay were evident in patients with HOCM compared to controls. Baseline and peak exercise LDT(RR) values were inversely related to cardiac output reserve and exercise duration. In multivariate analysis, LDT(RR) at peak exercise was identified as an independent predictor of cardiac output reserve.

CONCLUSIONS

In HOCM, baseline abnormalities of the relative duration of LV systolic and diastolic time aggravate during exercise. The disproportionate shortening of diastolic time may significantly impair cardiac efficiency by restricting diastolic filling.

Biphasic left ventricular outflow and its mechanism in hypertrophic obstructive cardiomyopathy

BACKGROUND

Biphasic systolic velocity in the left ventricular (LV) outflow tract (LVOT) occurs in hypertrophic obstructive cardiomyopathy (HOCM). The cause and importance of this observation remain poorly understood.

METHODS

A total of 25 patients with HOCM were matched to 30 control subjects. A function derived from the relation of flow in the proximal descending aorta to that in the LVOT was used to estimate the LVOT systolic flow rate in HOCM. Patients with HOCM were grouped by absence (group I) or presence (group II) of biphasic LVOT velocity.

RESULTS

Biphasic LVOT velocity was associated with biphasic estimated LVOT outflow (P =.002). The LVOT pressure gradient was inversely related to LV outflow rate at the time of the peak gradient (r = -.64, P <.001). Dobutamine increased the gradient and reduced LVOT outflow at the time of the peak gradient. In group II, mitral-septal separation occurred despite a LVOT gradient (36 mm Hg).

CONCLUSION

Biphasic LVOT flow in HOCM occurs and may be caused by "afterload mismatch." The late systolic increase in flow is related to mitral-septal separation. Resolution of systolic anterior motion occurs despite a persistent LVOT pressure gradient, implying a role for forces other than pressure differences.

Pulmonary hypertension and cardiac function in adult cystic fibrosis: role of hypoxemia

STUDY OBJECTIVES

To determine (1) the prevalence of pulmonary hypertension and cardiac dysfunction in adult cystic fibrosis (CF) patients with severe lung disease, (2) the relationship between these cardiovascular abnormalities and hypoxemia, and (3) the impact of subclinical pulmonary hypertension on survival.

DESIGN

Single-blind, cross-sectional study.

SETTING

Ambulatory clinic of the Adult CF program at a tertiary-level hospital.

PATIENTS

Clinically stable patients with severe lung disease (FEV1 < 40% of predicted normal value) who were not receiving supplemental oxygen. A second cohort of patients in stable condition with less severe lung disease (FEV1 40 to 65% predicted) was also recruited to enable multivariate analysis for the determinants of pulmonary hypertension.

MEASUREMENTS AND RESULTS

Eighteen patients with severe lung disease (FEV1 28 +/- 7% of predicted normal value) were initially studied. Each patient had overnight polysomnography, pulmonary function tests, and Doppler echocardiography. Arterial oxygen saturation (SaO2) was reduced during wakefulness (87.1 +/- 6.1%) and fell during sleep (84.0 +/- 6.6%) while transcutaneous PCO2 was normal during wakefulness (41.1 +/- 6.9 mm Hg) and increased during sleep (46.6 +/- 4.7 mm Hg). Left ventricular size, systolic function, and diastolic function were normal except in one patient who had had a previous silent myocardial infarction due to coronary artery disease. Qualitative assessment of right ventricular function was normal in all patients. Pulmonary artery systolic pressure (PASP) was increased (> 35 mm Hg) in seven patients without clinical evidence of cor pulmonale. Regression analysis was performed by combining these data with data from an additional 15 CF patients with moderately severe lung disease (FEV1 56.3 +/- 8.9% predicted normal) who were recruited to a modified study protocol that included overnight oximetry, pulmonary function tests, and Doppler echocardiography. None of these patients had evidence of hypoxemia and only three had mild elevation of PASP (36, 37, and 39 mm Hg). Linear regression analysis revealed that PASP was significantly correlated with FEV1 (r = -0.44; p = 0.013), and SaO2 during wakefulness (r =-0.60; p = 0.0003), during sleep (r = -0.56; p = 0.0008), and after 6 min of exercise (r = -0.75; p < 0.0001). Multivariate analysis revealed that awake SaO2 was a significantly better predictor of PASP than FEV1 (p = 0.0104). Clinical follow-up of the original cohort for up to 5 years revealed that mortality was significantly higher in those with pulmonary hypertension than those without pulmonary hypertension (p = 0.0129).

CONCLUSIONS

In adult CF patients with severe stable lung disease, left and right ventricular function is well maintained in the absence of significant coronary artery disease; pulmonary hypertension develops in a significant proportion of patients and is strongly correlated with oxygen status, independent of lung function; and subclinical pulmonary hypertension is associated with an increased mortality.

Mechanism of benefit of negative inotropes in obstructive hypertrophic cardiomyopathy

BACKGROUND

Drugs with negative inotropic effect are widely used to decrease obstruction in hypertrophic cardiomyopathy (HCM). However, the mechanism of therapeutic benefit has not been studied.

METHODS AND RESULTS

We used M-mode, two-dimensional, and pulsed Doppler echocardiography to study 11 patients with obstructive HCM before and after medical elimination of left ventricular outflow tract obstruction. We measured 148 digitized pulsed Doppler tracings recorded in the left ventricular cavity 2.5 cm apical of the mitral valve. Successful treatment slowed average acceleration of left ventricular ejection by 34% (P=.001). Mean time to peak velocity in the left ventricle was prolonged 31% (P=.001). Mean time to an ejection velocity of 60 cm/s was prolonged 91% (P=.001). Before treatment, left ventricular ejection velocity peaked in the first half of systole; after successful treatment, it peaked in the second half (P=.001). In contrast, after treatment, we found no change in peak left ventricular ejection velocity. We also found no change in the distance between the mitral coaptation point and the septum, as measured in two planes, indicating no treatment-induced alteration of this anatomic relationship.

CONCLUSIONS

Medical treatment eliminates mitral-septal contact and obstruction by decreasing left ventricular ejection acceleration. By slowing acceleration, treatment reduces the hydrodynamic force on the protruding mitral leaflet and delays mitral-septal contact. This, in turn, results in a lower final pressure gradient.

Mid-systolic drop in left ventricular ejection velocity in obstructive hypertrophic cardiomyopathy--the lobster claw abnormality

In many patients with obstructive hypertrophic cardiomyopathy, an abrupt mid-systolic drop in left ventricular ejection velocity can be detected. We analyzed 27 patients with obstructive hypertrophic cardiomyopathy who had 43 echocardiographic examinations (mean gradient 53 +/- 6 mm Hg). Exams showing a mid-systolic drop had higher mean outflow tract pressure gradients (90 +/- 6 compared with 29 +/- 4 mm Hg, p < 0.001). After medical elimination of obstruction, the mid-systolic drop was no longer seen. We measured 105 pulsed-wave Doppler tracings in the left ventricular cavity and compared them with 90 continuous-wave tracings through the outflow tract. There was a close temporal correlation between the nadir of the left ventricular velocity drop and the peak continuous-wave left ventricular outflow tract velocity (r = 0.99). There was also a close temporal correlation between the onset of the fall in pulsed velocity and the onset of M-mode mitral-septal contact (r = 0.95).

CONCLUSIONS

The mid-systolic drop in left ventricular velocity is due to impedance to ejection and provides evidence of true obstruction. As left ventricular ejection velocity falls to its mid-systolic nadir because of impedance of ejection, velocity downstream in the left ventricular outflow tract actually rises to its peak. This disparity in the two velocities, deceleration in the left ventricular cavity and acceleration in the left ventricular outflow tract, indicates that the outflow orifice is progressively narrowed over time as the mitral valve is forced into the septum by the rising pressure difference. The obstruction phase is best described as a time-dependent, amplifying feedback loop. The orifice narrows over time because of the rising pressure difference; the pressure difference rises over time because of the narrowing orifice.

Hypertrophic cardiomyopathy. Clinical spectrum and treatment

HCM is a heterogeneous disease genotypically, phenotypically, pathophysiologically, clinically, and therapeutically. In decisions on the management of these patients, it is important to recognize this heterogeneity and to direct therapy at the predominant abnormalities.

Echocardiographic Management of Patients With Hypertrophic Obstructive Ca rdiomyopathy Treated With Dual Chamber Pacemakers

A 53-year-old man diagnosed and treated for hypertrophic obstructive cardiomyopathy received serial echocardiograms before and after dual-chamber pacemaker implantation. Varying the programmed atrioventricular delay in a dual-chamber pacemaker can affect the left ventricular outflow tract pressure gradient in hypertrophic obstructive cardiomyopathy. Serial Doppler echo examinations were used to evaluate the effect of varying atrioventricular intervals. Echocardiography can be effectively used with pacemaker programming to optimize the left ventricular outflow tract velocities in patients with hypertrophic obstructive cardiomyopathy.

Ventricular function in snorers and patients with obstructive sleep apnea

We hypothesized that intermittent hypoxemia and increased ventricular afterload due to obstructive apnea during sleep (OSA) would cause chronic left ventricular dysfunction. Overnight polysomnography, M-mode and two-dimensional echo-Doppler studies while awake were performed on 51 consecutive snorers, 30 with OSA and 21 without apnea. Patients with previous myocardial infarction, awake hypoxemia or hypercapnia, or other causes of nocturnal hypoxemia were excluded. Echo-Doppler measurements included end-diastolic right and left ventricular dimensions and wall thickness, indices of left ventricular systolic performance (fractional shortening, ejection fraction and ejection time and diastolic performance, (isovolumic relaxation time, ratio of peak early [E] to late [A] diastolic transmitral flow and mitral pressure half-time). Both OSA patients and nonapneic snorers were of similar age. Although OSA patients were heavier, had a greater apnea-hypopnea index, and significant nocturnal hypoxemia, their echo-Doppler measurements were within normal limits and were not significantly different from nonapneic snorers. It is concluded that isolated obstructive sleep apnea does not cause chronic left ventricular dysfunction.

Doppler echocardiographic assessment of the pressure gradient during bicycle ergometry in hypertrophic cardiomyopathy

To assess the behavior of the subvalvular pressure gradient under physical exercise, 13 patients with obstructive hypertrophic cardiomyopathy were examined during upright bicycle ergometry by means of Doppler echocardiography. Additionally, right-sided cardiac catheterization was performed within 7 days. In 10 patients adequate Doppler tracings could be obtained during exercise. The Doppler-derived systolic pressure gradient increased from 75 +/- 24 to 140 +/- 42 mm Hg (p less than 0.0005). This was associated with an increase in the duration of the systolic mitral-septal contact from 59 +/- 21 to 136 +/- 28 ms (p less than 0.0005). Correlation between the pressure gradient and the duration of mitral-septal contact at rest and during exercise was good (r = 0.86), whereas correlation between the resting and exercise pressure gradient (r = 0.34) did not reach statistical significance. The increase in stroke volume during exercise, from 90 +/- 18 to 95 +/- 24 ml, was significant (p less than 0.05) but minimal. Therefore, only a moderate increase in systolic flow, from 205 +/- 54 to 268 +/- 78 ml/s (p less than 0.0005), was observed. Outflow tract resistance, defined as the ratio of the pressure gradient to systolic flow, increased from 0.38 +/- 0.11 to 0.57 +/- 0.24 mm Hg.s/ml (p less than 0.01). Thus, in a selected group of patients with hypertrophic cardiomyopathy a substantial increase in the maximal pressure gradient during upright bicycle ergometry was demonstrated in most patients. Exercise Doppler echocardiography may be valuable to assess the hemodynamic significance of obstruction in individual patients in a physiologic setting and has a potential to monitor the effect of therapeutic interventions.

Hypertrophic cardiomyopathy: prognosis with medical or surgical therapy

Over the past 30 years, knowledge of the natural history and effects of therapy in patients with hypertrophic cardiomyopathy has expanded greatly, but progress has been hampered by its variable patterns of expression. Many but not all patients show symptomatic improvement with medical treatment. Chronic beta blockage does not appear to affect long-term survival, whereas results with calcium channel blockade by verapamil have been encouraging; however, they await confirmation, and verapamil may be hazardous in some patients with severe left ventricular (LV) outflow tract obstruction and elevated LV end-diastolic pressure. Reported beneficial effects of amiodarone on survival also require further study. Surgical therapy has become the treatment of choice for medically refractory patients with proven outflow tract obstruction. In several centers, the operative risk is low, and long-term follow-up demonstrates prolonged symptomatic relief. It is hoped that work currently underway will provide more definitive information on the long-term effects of the role of calcium channel blockers, antiarrhythmic medications, and the long-term effects of surgical therapy on survival of patients with this disorder.