Early changes in the time course of myocardial contraction after correcting aortic regurgitation

Challenges and opportunities in improving left ventricular remodelling and clinical outcome following surgical and trans-catheter aortic valve replacement

Over the last half century, surgical aortic valve replacement (SAVR) has evolved to offer a durable and efficient valve haemodynamically, with low procedural complications that allows favourable remodelling of left ventricular (LV) structure and function. The latter has become more challenging among elderly patients, particularly following trans-catheter aortic valve implantation (TAVI). Precise understanding of myocardial adaptation to pressure and volume overloading and its responses to valve surgery requires comprehensive assessments from aortic valve energy loss, valvular-vascular impedance to myocardial activation, force-velocity relationship, and myocardial strain. LV hypertrophy and myocardial fibrosis remains as the structural and morphological focus in this endeavour. Early intervention in asymptomatic aortic stenosis or regurgitation along with individualised management of hypertension and atrial fibrillation is likely to improve patient outcome. Physiological pacing via the His-Purkinje system for conduction abnormalities, further reduction in para-valvular aortic regurgitation along with therapy of angiotensin receptor blockade will improve patient outcome by facilitating hypertrophy regression, LV coordinate contraction, and global vascular function. TAVI leaflet thromboses require anticoagulation while impaired access to coronary ostia risks future TAVI-in-TAVI or coronary interventions. Until comparable long-term durability and the resolution of TAVI related complications become available, SAVR remains the first choice for lower risk younger patients.

Systole-diastole mismatch in hypertrophic cardiomyopathy is caused by stress induced left ventricular outflow tract obstruction

BACKGROUND

Pharmacological stress is used to assess the degree of left ventricular (LV) subvalvular gradient in patients with hypertrophic cardiomyopathy (HCM), but there is little information about associated physiological changes.

METHODS

Echocardiography-Doppler ultrasound scanning measurements in 23 patients with HCM and 23 control subjects of similar age were studied at rest and at the end point of dobutamine stress.

RESULTS

In patients, the systolic time was normal at rest, but increased abnormally with stress. In patients, the total isovolumic contraction time failed to shorten, and the total ejection time increased abnormally. Changes in total ejection time correlated with an increase in peak subvalvular gradient in control subjects and patients (r = 0.52 and r = 0.66, respectively; P <.01 for both). In patients, the diastolic time was normal at rest, but shortened abnormally with stress. In patients, the isovolumic relaxation time fell abnormally, as did the filling time. Mitral E wave acceleration and left atrium size were unchanged with stress in control subjects, but consistently increased in patients with HCM, which indicates an increased early diastolic atrioventricular pressure gradient.

CONCLUSION

In HCM, systolic period increases abnormally with stress. This is not because of a loss of inotropy, but is directly related to the degree of LV outflow tract obstruction. As a result, the diastolic period fails to increase, reducing the time available for coronary flow, the LV filling pattern is modified, and the diastolic atrioventricular pressure gradient increases. These changes may contribute to symptom development and suggest why reducing LV outflow tract obstruction per se may be therapeutically useful in HCM.

The relationship of myocardial stroke work to coronary flow velocity immediately after aortic valve replacement

BACKGROUND

The interrelations between myocardial stroke work and coronary flow velocity have not been fully defined during aortic valve replacement or with different cardioplegias.

METHODS

Twenty-six patients (15 men age 63+/-13 years) who had elective isolated aortic valve replacement were studied by transesophageal Doppler echocardiography with simultaneous high fidelity left ventricular pressure. Fifteen patients received cold blood cardioplegia and 11 had warm blood cardioplegia. Myocardial stroke work and flow velocities in proximal left anterior descending coronary artery were quantified simultaneously before cardiopulmonary bypass and at 1, 6, 12, and 20 hours afterwards.

RESULTS

Myocardial stroke work decreased postoperatively in both groups (160+/-19 versus 228+/-19 mJ/cm3 per minute, with cold blood cardioplegia; 135+/-22 versus 227+/-22 mJ/cm3 per minute with warm blood cardioplegia; both p<0.001 versus time, but p>0.05 versus cardioplegia, by two-way analysis of variance). Left anterior descending artery flow velocity-time integral per minute increased significantly in both groups (26.1+/-2.1 versus 15.0+/-2.1 m/min with cold blood cardioplegia; 32.8+/-2.5 versus 14.4+/-2.5 m/min with warm blood cardioplegia; both p<0.001 versus time, but p>0.05 versus cardioplegia). Thus, at 1 hour postoperatively the mJ x cm(-3) x m(-1) x min ratio of myocardial stroke work to left anterior descending artery flow velocity-time integral decreased significantly in both groups (4.3+/-1.6 versus 16.3+/-1.7 mJ x cm(-3) x m(-1) x min with warm blood cardioplegia, and 7.4+/-1.4 versus 17.9+/-1.4 J x cm(-3) x m(-1) x min with cold blood cardioplegia; both p<0.001 versus time). Warm blood cardioplegia was also associated with a lower mean ratio perioperatively than that with cold blood cardioplegia (7.8+/-0.9 versus 10.9+/-0.7 mJ x cm(-3) x m(-1) x min, p = 0.014).

CONCLUSIONS

Coronary hyperemia occurs for at least 20 hours postoperatively when myocardial stoke work has decreased. The ratio of myocardial stroke work to coronary flow velocity appears to be more sensitive than either alone in differentiating the effect of warm versus cold blood cardioplegia.