Difference in coronary blood flow dynamics between patients with hypertension and those with hypertrophic cardiomyopathy

Physiologically personalized coronary blood flow model to improve the estimation of noninvasive fractional flow reserve

PURPOSE

Coronary outlet resistance is influenced by the quantification and distribution of resting coronary blood flow. It is crucial for a more physiologically accurate estimation of fractional flow reserve (FFR) derived from computed tomography angiography (CTA), referred to as FFRCT. This study presents a physiologically personalized (PP)-based coronary blood flow model involving the outlet boundary condition (BC) and a standardized outlet truncation strategy to estimate the outlet resistance and FFRCT.

METHODS

In this study, a total of 274 vessels were retrospectively collected from 221 patients who underwent coronary CTA and invasive FFR within 14 days. For FFRCT determination, we have employed a PP-based outlet BC model involving personalized physiological parameters and left ventricular mass (LVM) to quantify resting coronary blood flow. We evaluated the improvement achieved in the diagnostic performance of FFRCT by using the PP-based outlet BC model relative to the LVM-based model, with respect to the invasive FFR. Additionally, in order to evaluate the impact of the outlet truncation strategy on FFRCT, 68 vessels were randomly selected and analyzed independently by two operators, by using two different outlet truncation strategies at 1-month intervals.

RESULTS

The per-vessel diagnostic performance of the PP-based outlet BC model was improved, based on invasive FFR as reference, compared to the LVM-based model: (i) accuracy/sensitivity/specificity: 91.2%/90.4%/91.8% versus 86.5%/84.6%/87.6%, for the entire dataset of 274 vessels, (ii) accuracy/sensitivity/specificity: 88.7%/82.4%/90.4% versus 82.4%/ 76.5%/84.0%, for moderately stenosis lesions. The standardized outlet truncation strategy showed good repeatability with the Kappa coefficient of 0.908.

CONCLUSIONS

It has been shown that our PP-based outlet BC model and standardized outlet truncation strategy can improve the diagnostic performance and repeatability of FFRCT.

Biomarker changes with systolic anterior motion of the mitral valve in cats with hypertrophic cardiomyopathy

BACKGROUND

N-terminal pro B-type natriuretic peptide (NT-proBNP) and cardiac troponin-I (cTnI) are biomarkers commonly evaluated in cats with suspected heart disease. Many cats with hypertrophic cardiomyopathy (HCM) have systolic anterior motion of the mitral valve (SAM), but its influence on circulating NT-proBNP or cTnI concentrations is currently unknown.

HYPOTHESIS/OBJECTIVES

Cats with HCM and SAM (HCM^SAM+ ) have higher NT-proBNP and cTnI concentrations than do cats with HCM but without SAM (HCM^SAM- ).

ANIMALS

One hundred forty cats with HCM: 70 with SAM and 70 without SAM.

METHODS

Retrospective case-to-case study. Cats were recruited if diagnosed with HCM by echocardiography and results were available for NT-proBNP or cTnI concentrations or both. Cats with SAM were matched to those without SAM for clinical presentation, left atrial (LA) size and left ventricular (LV) fractional shortening.

RESULTS

A total of 119 NT-proBNP and 123 cTnI results were available. The HCM^SAM+ cats had higher median concentrations than did HCM^SAM- cats for NT-proBNP (729 pmoL/L; interquartile range [IQR], 275-1467 versus 65 pmoL/L; IQR, 25-271; P < .001) and cTnI (0.27 ng/mL; IQR, 0.10-0.81 versus 0.07 ng/mL; IQR, 0.01-0.43; P = .002). In general linear models for both NT-proBNP and cTnI, the independent explanatory variables were SAM, congestive heart failure, maximal LV wall thickness, and LA size.

CONCLUSIONS AND CLINICAL IMPORTANCE

For cats with HCM and equivalent LA size and LV systolic function, those with SAM had higher NT-proBNP and cTnI concentrations than did those without SAM. Presence of SAM should be considered when interpreting biomarker concentrations in cats with HCM.

Hierarchical structural component model for pathway analysis of common variants

BACKGROUND

Genome-wide association studies (GWAS) have been widely used to identify phenotype-related genetic variants using many statistical methods, such as logistic and linear regression. However, GWAS-identified SNPs, as identified with stringent statistical significance, explain just a small portion of the overall estimated genetic heritability. To address this 'missing heritability' issue, gene- and pathway-based analysis, and biological mechanisms, have been used for many GWAS studies. However, many of these methods often neglect the correlation between genes and between pathways.

METHODS

We constructed a hierarchical component model that considers correlations both between genes and between pathways. Based on this model, we propose a novel pathway analysis method for GWAS datasets, Hierarchical structural Component Model for Pathway analysis of Common vAriants (HisCoM-PCA). HisCoM-PCA first summarizes the common variants of each gene, first at the gene-level, and then analyzes all pathways simultaneously by ridge-type penalization of both the gene and pathway effects on the phenotype. Statistical significance of the gene and pathway coefficients can be examined by permutation tests.

RESULTS

Using the simulation data set of Genetic Analysis Workshop 17 (GAW17), for both binary and continuous phenotypes, we showed that HisCoM-PCA well-controlled type I error, and had a higher empirical power compared to several other methods. In addition, we applied our method to a SNP chip dataset of KARE for four human physiologic traits: (1) type 2 diabetes; (2) hypertension; (3) systolic blood pressure; and (4) diastolic blood pressure. Those results showed that HisCoM-PCA could successfully identify signal pathways with superior statistical and biological significance.

CONCLUSIONS

Our approach has the advantage of providing an intuitive biological interpretation for associations between common variants and phenotypes, via pathway information, potentially addressing the missing heritability conundrum.

Obesity is associated with worse long-term outcomes in hypertrophic cardiomyopathy patients with acute myocardial infarction

BACKGROUND

Hypertrophic cardiomyopathy is associated with poor prognosis. In our previous study, it has been reported that patients with acute myocardial infarction and hypertrophic cardiomyopathy exhibited worse long-term outcomes than those with acute myocardial infarction without hypertrophic cardiomyopathy and those with hypertrophic cardiomyopathy without acute myocardial infarction. In this article, we aimed to assess the impact of body mass index on the long-term outcomes of hypertrophic cardiomyopathy patients with acute myocardial infarction.

METHODS

Seventy-eight consecutive patients with hypertrophic cardiomyopathy and acute myocardial infarction were included. Obesity was defined as body mass index ⩾28 kg/m² adapted to Chinese. The long-term endpoints were major adverse cardiac events and secondary endpoints, which included re-hospitalization, recurrent angina, thrombosis, bleeding, heart failure, and arrhythmias.

RESULTS

There were no differences in observed in-hospital mortality or 5-year mortality between the two groups of hypertrophic cardiomyopathy and acute myocardial infarction patients divided by body mass index. However, significantly increased incidence of re-percutaneous coronary intervention and stroke was observed in the obese group (re-percutaneous coronary intervention: 0.0% vs. 21.4%, p = 0.007; stroke: 5.6% vs. 28.6%, p = 0.042). The 5-year outcomes of major adverse cardiac events were inferior in the obese group (log-rank p = 0.020).

CONCLUSION

Acute myocardial infarction and hypertrophic cardiomyopathy patients who were obese exhibited worse long-term outcomes than those without obesity.

Long-Term Outcomes of Acute Myocardial Infarction in Patients With Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is associated with poor prognosis. It has been reported that there is no difference in in-hospital mortality after acute myocardial infarction (AMI) between patients with and without HCM. However, whether there are differences in long-term outcomes after AMI between patients with and without HCM remains unclear. In this study, we analyzed the clinical profiles of 78 consecutive patients with HCM and AMI (HCM and AMI group), 78 sex- and age-matched patients with AMI and without HCM (AMI group), and 78 sex- and age-matched patients with HCM and without AMI (HCM group). The study end points were major adverse cardiac events (MACEs) and secondary end points. During the follow-up period of 4.8 ± 3.6 years, MACEs occurred in 19 (27.9) patients in the HCM and AMI group, in 11 (16.7%) patients in the AMI group, and in 8 (12.3%) patients in the HCM group. The long-term outcomes of the HCM and AMI group were inferior to that of the other 2 groups (log-rank P = .030 for MACEs, log-rank P = .032 for secondary end points). In conclusion, patients with AMI with HCM exhibited worse long-term outcomes than did patients with AMI without HCM and patients with HCM without AMI.

Enhanced endothelin-1/Rho-kinase signalling and coronary microvascular dysfunction in hypertensive myocardial hypertrophy

AIMS

Hypertensive cardiac hypertrophy is associated with reduced coronary flow reserve, but its impact on coronary flow regulation and vasomotor function remains incompletely understood and requires further investigation.

METHODS AND RESULTS

Left ventricular hypertrophy was induced in mice by transverse aortic coarctation (TAC) for 4 weeks. The left coronary artery blood velocity (LCABV) and myocardium lactate level were measured following the metabolic activation by isoproterenol. Septal coronary arterioles were isolated and pressurized for functional studies. In TAC mice, the heart-to-body weight ratio was increased by 45%, and cardiac fractional shortening and LCABV were decreased by 51 and 14%, respectively. The resting myocardial lactate level was 43% higher in TAC mice. Isoproterenol (5 µg/g, i.p.) increased heart rate by 20% in both groups of animals, but the corresponding increase in LCABV was not observed in TAC mice. The ventricular hypertrophy was associated with elevation of myocardial endothelin-1 (ET-1), increased vascular expression of rho-kinases (ROCKs), and increased superoxide production in the myocardium and vasculature. In coronary arterioles from TAC mice, the endothelial nitric oxide (NO)-mediated dilation to acetylcholine (ACh) was reversed to vasoconstriction and the vasoconstriction to ET-1 was augmented. Inhibition of ROCK by H-1152 alleviated oxidative stress and abolished enhanced vasoconstriction to ET-1. Both H-1152 and superoxide scavenger Tempol abolished coronary arteriolar constriction to ACh in a manner sensitive to NO synthase blocker NG-nitro-L-arginine methyl ester.

CONCLUSIONS

Myocardial hypertrophy induced by pressure overload leads to cardiac and coronary microvascular dysfunction and ischaemia possibly due to oxidative stress, enhanced vasoconstriction to ET-1 and compromised endothelial NO function via elevated ROCK signalling.

Considerations in Understanding the Coronary Blood Flow- Left Ventricular Mass Relationship in Patients with Hypertension

Abstract: Background: Coronary blood flow (CBF) is essential for optimal cardiac performance and to maintain myocardial viability. There is considerable ambiguity concerning CBF in hypertension.

Objective: To investigate the relationship between CBF and left ventricular (LV) mass in persons with hypertension.

Methods: OvidSP Medline was systematically searched. Eligible articles assessed CBF, and LV mass in adults with and without hypertension (HTN).

Results: Eleven studies met the entry criteria. All 8 studies reported an increase in CBF (ml/min) for persons with hypertension (N=212) compared to individuals without hypertension (N=150). Meta-analysis showed a significant and 2.88 fold higher CBP in hypertension. Six studies adjusted CBF for LV mass; of which 4 studies reported a reduction in CBF. Meta-analysis showed a significant decrease in CBF/g LV mass in hypertension. The two studies that did not show a decrease in CBF, used the argon chromatographic method to measure coronary sinus blood flow suggesting this methodology may have influenced the results. Using the mean CBF in normotensive group to construct the expected CBF according to LV mass, reported CBF in HTN was progressively less than expected In two studies, (N=142), there was a significant inverse correlation between LV mass and CBF/ g LV mass. Multivariate analysis (three studies) consistently found a highly significant independent relationship between LV mass and CBF after considering age, sex, heart rate and several other factors.

Conclusion: Hypertension is associated with a reduction in CBF adjusted for LV mass with a highly significant inverse association between CBF and LV mass. Clinicians should be aware that patients with hypertension are at greater risk for myocardial ischemia should develop other factors that limit CBF or myocardial oxygen delivery.

Assessment of Coronary Flow Reserve by Adenosine Stress Myocardial Perfusion Imaging in Patients with Hypertension

In this study, our aim was to assess the coronary flow reserve (CFR) by performing the adenosine stress (99m)Tc-MIBI single-photon computed tomographic (SPECT) myocardial perfusion imaging in patients with hypertension. 47 hypertensive patients with normal coronary angiography were divided into 2 groups, defined by the presence (LVH, n = 22) and absence (non-LVH, n = 25) of left ventricular hypertrophy with 17 normal cases as controls. All patients were administered the adenosine stress-rest (99m)Tc-MIBI scintigraphy. 0.14 mg/kg/min adenosine was administered by continuous infusion for 6 min. We found that adenosine-induced myocardial ischemia was present in 26 cases (55.3 %) with 87 segments (20.6 %) showing abnormal distribution in the hypertensive group versus a single case (5.9 %) (χ (2) = 31.12, P < 0.001) and segment (0.7 %) (χ (2) = 32.90, P < 0.001) in the control group by SPECT perfusion. In the LVH group, 17 cases (77.3 %) and 67 segments (33.8 %) of myocardial ischemia were present. In the non-LVH group, there were 9 cases (36.0 %) (χ (2) = 8.06, P < 0.001), 20 segments (8.9 %) (χ (2) = 40.13, P < 0.001). There was a significant decrease in coronary reserve in the hypertensive groups following adenosine infusion with a fourfold decrease in cases and a sixfold decrease in segments (P < 0.001). Our study suggests that assessing CFR by the (99m)Tc-MIBI adenosine stress by SPECT imaging is a relatively easy, safe, and non-invasive test in patients with hypertension. We noted a decrease in CFR in patients with hypertension. This decrease was especially remarkable for hypertensive patients with LVH. This study shows that administering the (99m)Tc-MIBI adenosine stress by SPECT imaging is a safe, simple, and non-invasive test for detecting CFR in patients with hypertension.

Peripheral microvascular function is altered in young individuals at risk for hypertrophic cardiomyopathy and correlates with myocardial diastolic function

Hypertrophic cardiomyopathy (HCM) is a major cause of sudden cardiac death in the young. Based on previous reports of functional abnormalities in not only coronary but also peripheral vessels in adults with HCM, we aimed to assess both peripheral vascular and myocardial diastolic function in young individuals with an early stage of HCM and in individuals at risk for HCM. Children, adolescents, and young adults (mean age: 12 yr) with a family history of HCM who either had (HCM group; n = 36) or did not have (HCM-risk group; n = 30) echocardiography-documented left ventricular (LV) hypertrophy as well as healthy matched controls (n = 85) and healthy young athletes (n = 12) were included in the study. All underwent assessment with 12-lead electrocardiography, two-dimensional echocardiography, tissue Doppler imaging and laser Doppler with transdermal iontophoresis of ACh and sodium nitroprusside. LV thickness and mass were increased in HCM and athlete groups compared with control and HCM-risk groups. The mitral E-to-e' ratio, measured via tissue Doppler, was increased in HCM (P < 0.0001) and HCM-risk (P < 0.01) groups compared with control and athlete groups, as were microvascular responses to ACh (HCM group: P = 0.045 and HCM-risk group: P = 0.02). Responses to ACh correlated with the E-to-e' ratio (r = 0.5, P = 0.001). Microvascular responses to sodium nitroprusside were similar in all groups (P > 0.2). HCM-causing mutations or its familial history are associated with changes in cardiac diastolic function and peripheral microvascular function even before the onset of myocardial hypertrophy. Tissue Doppler can be used to differentiate HCM from physiological LV hypertrophy in young athletes.

Differences in coronary blood flow in aortic regurgitation and systemic arterial hypertension have implications for diastolic blood pressure targets: a systematic review and meta-analysis

The objective was to evaluate coronary blood flow (CBF) in patients with systemic arterial hypertension (HTN) and to compare it with CBF in patients with aortic regurgitation (AR). A systematic literature search was conducted using the reference terms "coronary blood flow" and either "aortic regurgitation" or "hypertension." The selection criteria included CBF measurement in a concomitant control group, except studies evaluating CBF with aortic-valve replacement surgery. Twenty-two studies met the inclusion criteria. There were 318 persons with HTN, with 185 controls; and 102 persons with AR, with 144 controls. Despite an overall increase in CBF in HTN, CBF per gram of left ventricular mass was significantly (P < 0.0001) reduced. In contrast, CBF per gram of left ventricular mass was significantly (P = 0.004) increased in AR. Aortic regurgitation was associated with a significant (P < 0.0001) increase in CBF during systole and away from diastole, in contrast to persons with HTN. Aortic-valve replacement reversed the increase in systolic CBF. These data suggest that patients with HTN are more vulnerable than patients with AR to lower diastolic blood pressure (DBP), because resting CBF is compromised in HTN. Furthermore, patients with HTN may not compensate for DBP reductions by shifting CBF to systole, such as can occur with the low DBP in AR. Lower DBP in patients with AR cannot be used to justify treating patients with HTN to similar DBP because of the dramatic differences in CBF between the 2 conditions.

Coronary flow reserve in hypertrophic cardiomyopathy: relation with microvascular dysfunction and pathophysiological characteristics

BACKGROUND.: The decrease in coronary flow reserve (CFR) in hypertrophic cardiomyopathy (HCM) predisposes to myocardial ischaemia, systolic dysfunction and cardiac death. In this study we investigate to which extent haemodynamic, echocardiographic, and histological parameters contribute to the reduction of CFR. METHODS.: In ten HCM patients (mean age 44+/-14 years) and eight heart transplant (HTX) patients (mean age 51+/-6 years) CFR was calculated in the left anterior descending coronary artery. In all subjects haemodynamic, echocardiographic and histological parameters were assessed. The relationship between these variables and CFR was determined using linear regression analysis. RESULTS.: CFR was reduced in HCM compared with HTX patients (1.6+/-0.7 vs. 2.7+/-0.8, p<0.01). An increase in septal thickness (p<0.005), indexed left ventricular (LV) mass (p<0.005), LV end-diastolic pressure (p<0.001), LV outflow tract gradient (p<0.05) and a decrease in arteriolar lumen size (p<0.05) were all related to a reduction in CFR. CONCLUSION.: In HCM patients haemodynamic (LV end-diastolic pressure, LV outflow tract gradient), echocardiographic (indexed LV mass) and histological (% luminal area of the arterioles) changes are responsible for a decrease in CFR. (Neth Heart J 2007;15:209-15.).

Diastolic flow velocity pattern of the left anterior descending coronary artery in hypertrophied heart, with special reference to the difference between hypertrophic cardiomyopathy and hypertensive left ventricular hypertrophy

BACKGROUND

This study aimed to clarify the characteristics of diastolic flow velocity pattern of the left anterior descending coronary artery (LAD) in patients with left ventricular hypertrophy (LVH), and the difference in diastolic LAD flow velocity pattern between hypertensive LVH and hypertrophic cardiomyopathy (HCM).

METHODS

The flow velocity pattern was recorded at the mid-portion of the LAD by high-frequency transthoracic Doppler echocardiography in 22 patients with HCM, 10 hypertensive patients with LVH [LVH(+)HT], and 9 hypertensive patients without LVH [LVH(-)HT]. The diastolic flow pattern was analyzed. Standard two-dimensional echocardiogram and apexcardiogram (ACG) were also recorded.

RESULTS

The interventricular septal thickness (IVST) and the sum of the IVST and LV posterior wall thickness (PWT) (IVST + PWT) were greater in HCM than in HT (p < 0.01) patients. Early diastolic upstroke time (D-UT) of the LAD flow velocity wave was longest in HCM, and was longer in LVH(+)HT than in LVH(-)HT (p < 0.01) patients. Direct correlation was found between D-UT and IVST, IVST + PWT in patients with LVH(+)HT and LVH(-)HT (r = 0.80, 0.79, respectively; p < 0.01), but no correlation was found between these parameters in HCM. Late-diastolic step (LDS) formation of the LAD flow velocity wave was observed in 68% of HCM, 20% of LVH(+)HT, but none of the LVH(-)HT patients. The A wave ratio of ACG was higher in patients with LDS than in those without (p < 0.01). The LDS occurred coincidently with the A wave of ACG.

CONCLUSIONS

The diastolic LAD flow velocity pattern in hypertrophied heart is characterized by slow acceleration and LDS formation, reflecting impaired relaxation and increased stiffness of the LV, respectively. These abnormalities correlate with the degree of hypertrophy in hypertensive heart, but do not correlate with that in HCM.

Hypertrophic and hypertensive hypertrophic cardiomyopathy--a true association?

The cardiomyopathies were previously defined as ''heart muscle diseases of unknown cause'' and were differentiated from specific heart muscle disease with known cause. With increasing understanding of etiology and pathogenesis, the difference between cardiomyopathy and specific heart muscle disease has become indistinct. The term specific cardiomyopathies are used to describe heart diseases that are associated with specific cardiac or systemic disorders. These were previously defined as specific heart muscle diseases. They included ischemic cardiomyopathy, valvular cardiomyopathy, hypertensive cardiomyopathy, inflammatory cardiomyopathy, metabolic cardiomyopathy, general system disease, muscular dystrophies, sensitivity and toxic reactions, and peripartal cardiomyopathy. The cardiomyopathies are therefore classified by the dominant pathophysiology or, if possible, by etiological/pathogenetic factors. Topol in 1985 described a syndrome called hypertensive hypertrophic cardiomyopathy that included severe concentric cardiac hypertrophy, a small left ventricular cavity, and supernormal indexes of systolic function without concurrent medical illness or ischemic heart disease. The aim of this review was to highlighted this syndrome from pathophysiological, clinical, diagnostical view and clear all the possible correlations with genetic, inflammatory, and other markers.

Biomarkers of pathophysiology in hypertrophic cardiomyopathy: implications for clinical management and prognosis

The study of biomarkers and their signalling pathways has allowed the development of new therapeutic strategies in a range of disorders. The aim of the present systematic review is to provide an overview of different biomarkers in patients with hypertrophic cardiomyopathy that could give some insight into the pathophysiologic mechanism(s) underlying the typical clinical and histological manifestations of the disease. Several pathophysiological models are presented and discussed, including studies that have investigated these biomarkers for diagnostic and prognostic reasons, in relation to disease progression and/or mortality.

Coronary flow velocity changes in response to hypercapnia: assessment by transthoracic Doppler echocardiography

BACKGROUND

The effects of hypercapnia on coronary arteries in human beings are not known. We used transthoracic Doppler echocardiography to evaluate coronary blood flow velocity (CFV) changes in response to hypercapnia in healthy adults.

METHODS

Twenty adults underwent transthoracic Doppler echocardiography of the left anterior descending coronary artery while breathing room air, 40% fraction of inspired oxygen, and 40% fraction of inspired oxygen with carbon dioxide supplemented to end-tidal tensions of +5, +7.5, and +10 mm Hg above baseline.

RESULTS

Mean (SD) diastolic peak CFV values for these conditions were 23.1 (9.1), 23.0 (9.0), 25.5 (9.3), 27.9 (11.5), and 31.5 (13.0) cm/s, respectively. Significant overall differences between conditions (P < .001) and progressive levels of hypercapnia (P < or = .01) were observed. CFV increases remained significant after adjusting for increases in cardiac output (P = .038).

CONCLUSIONS

CFV increases with hypercapnia. This is the first report of human coronary artery flow responses to hypercapnia. Transthoracic Doppler echocardiography methodology is feasible for measuring CFV and the effects of hypercapnia on the coronary circulation.

Cross-Talk Between Cardiac Muscle and Coronary Vasculature

The cardiac muscle and the coronary vasculature are in close proximity to each other, and a two-way interaction, called cross-talk, exists. Here we focus on the mechanical aspects of cross-talk including the role of the extracellular matrix. Cardiac muscle affects the coronary vasculature. In diastole, the effect of the cardiac muscle on the coronary vasculature depends on the (changes in) muscle length but appears to be small. In systole, coronary artery inflow is impeded, or even reversed, and venous outflow is augmented. These systolic effects are explained by two mechanisms. The waterfall model and the intramyocardial pump model are based on an intramyocardial pressure, assumed to be proportional to ventricular pressure. They explain the global effects of contraction on coronary flow and the effects of contraction in the layers of the heart wall. The varying elastance model, the muscle shortening and thickening model, and the vascular deformation model are based on direct contact between muscles and vessels. They predict global effects as well as differences on flow in layers and flow heterogeneity due to contraction. The relative contributions of these two mechanisms depend on the wall layer (epi- or endocardial) and type of contraction (isovolumic or shortening). Intramyocardial pressure results from (local) muscle contraction and to what extent the interstitial cavity contracts isovolumically. This explains why small arterioles and venules do not collapse in systole. Coronary vasculature affects the cardiac muscle. In diastole, at physiological ventricular volumes, an increase in coronary perfusion pressure increases ventricular stiffness, but the effect is small. In systole, there are two mechanisms by which coronary perfusion affects cardiac contractility. Increased perfusion pressure increases microvascular volume, thereby opening stretch-activated ion channels, resulting in an increased intracellular Ca2+transient, which is followed by an increase in Ca2+sensitivity and higher muscle contractility (Gregg effect). Thickening of the shortening cardiac muscle takes place at the expense of the vascular volume, which causes build-up of intracellular pressure. The intracellular pressure counteracts the tension generated by the contractile apparatus, leading to lower net force. Therefore, cardiac muscle contraction is augmented when vascular emptying is facilitated. During autoregulation, the microvasculature is protected against volume changes, and the Gregg effect is negligible. However, the effect is present in the right ventricle, as well as in pathological conditions with ineffective autoregulation. The beneficial effect of vascular emptying may be reduced in the presence of a stenosis. Thus cardiac contraction affects vascular diameters thereby reducing coronary inflow and enhancing venous outflow. Emptying of the vasculature, however, enhances muscle contraction. The extracellular matrix exerts its effect mainly on cardiac properties rather than on the cross-talk between cardiac muscle and coronary circulation.

Impact of intraventricular conduction delay on coronary haemodynamics: a study with intracoronary Doppler in patients with bundle branch blocks and normal coronary arteries

AIMS

The impact of right bundle branch block (RBBB) and left bundle branch block (LBBB) on myocardial perfusion is not completely understood as data are often blurred by underlying cardiac disease. The present study investigates whether conduction delays per se affect coronary perfusion-an indirect measure of myocardial oxygen demand.

METHODS AND RESULTS

Intracoronary Doppler and ultrasound were performed in 8 patients with RBBB, 10 patients with LBBB, and 10 control subjects. All patients had angiographically normal coronary arteries and normal left ventricular function. Baseline (bAPV) and adenosine-induced hyperaemic average flow velocity and coronary flow velocity reserve (CFVR) were measured in left anterior descending arteries. Intravascular ultrasound showed no difference in lumen cross-sectional area and plaque burden between groups. Patients with RBBB and LBBB had higher bAPV values than controls (19.0 +/- 4.9, 21.9 +/- 5.1, and 14.6 +/- 2.4 cm/s, respectively; ANOVA P = 0.003). There was no difference between patients with LBBB and RBBB compared with controls in CFVR (2.8 +/- 0.5, 3.0 +/- 1.0, and 3.4 +/- 0.7, respectively; ANOVA P = 0.21).

CONCLUSION

Bundle branch blocks, in particular LBBB, are associated with an increased coronary flow velocity, which indicates enhanced myocardial oxygen demand on the basis of mechanoenergetic disturbance. This may contribute to the unfavourable outcome of patients with intraventricular conduction delay.

Determinants of coronary blood flow in humans: quantification by intracoronary Doppler and ultrasound

The direct determinants of coronary flow are lumen area and blood flow velocity; however, the precise mechanisms that control these factors are not fully understood. The aim of the present study was to assess by which mechanisms lumen area and coronary flow velocity interact with hemodynamic and morphometric factors, thereby influencing coronary flow. Intracoronary Doppler and ultrasound measurements were performed in 28 patients without coronary lumen irregularities. Flow velocity and lumen cross-sectional area were measured in the proximal segments of all three coronary arteries. Global lumen cross-sectional area and global flow were obtained by adding up the values of all three coronary arteries. Left ventricular mass was assessed by echocardiography. Stress-mass-heart rate and pressure-rate products reflecting myocardial oxygen demand were calculated. Global coronary flow increased during adenosine-induced hyperemia from 197 +/- 72 to 637 +/- 204 ml/min (P < 0.001). Global coronary flow closely correlated with the stress-mass-heart rate product (r = 0.62; P < 0.001). Looking at the two constituents of flow separately, global coronary cross-sectional area was closely related to left ventricular muscle mass (r = 0.61; P < 0.001), whereas mean coronary flow velocity at rest showed a strong linear relation with the pressure-rate product (r = 0.64; P < 0.001). There was no interaction between cross-sectional area and blood flow velocity in any of the coronary vessels. Coronary lumen size and flow velocity, the two determinants of coronary flow, are principally determined by different physiological factors. Long-term flow adaptation is achieved by an increase in coronary lumen size, whereas short-term myocardial oxygen requirements are met by changes in resting flow velocity.

Adverse prognosis of patients with hypertrophic cardiomyopathy who have epicardial coronary artery disease

BACKGROUND

Adult patients with hypertrophic cardiomyopathy (HCM) may develop concomitant atherosclerotic coronary artery disease (CAD). There is a paucity of data on the clinical outcomes of HCM patients who have CAD.

METHODS AND RESULTS

We examined the outcome of 433 adult patients with HCM according to the presence and severity of CAD. All patients were aged > or =21 years, had a left ventricular ejection fraction of > or =50%, and were without a history of prior surgical revascularization (mean age, 63 years; 212 men). Compared with HCM patients with mild-to-moderate or no CAD, those with severe CAD demonstrated markedly reduced survival. Ten-year overall survival was 46.1%, 70.5%, and 77.1% for patients with severe, mild-to-moderate, and no CAD, respectively (unadjusted P=0.0001; adjusted P=0.0006). For the end point of cardiac death, this survival was 62.3%, 81.0%, and 80.9% (unadjusted P=0.009; adjusted P=0.004). For the end point of sudden cardiac death, this survival was 77.4%, 93.2%, and 90.3% (unadjusted P=0.01; adjusted P=0.01). The presence of severe CAD also was highly predictive of these events (risk ratio for respective event: 2.31, 2.15, and 2.77) in multivariate models that additionally identified age, prior stroke, hyperlipidemia, and atrial fibrillation as significant covariates.

CONCLUSIONS

Among adult patients with HCM who undergo coronary angiography, those who have concomitant severe CAD are at increased risk of death. This risk far exceeds historical death rates of CAD patients with normal left ventricular function.