Mechanisms of coronary microcirculatory dysfunction in patients with aortic stenosis and angiographically normal coronary arteries

Determinants of coronary microvascular dysfunction in symptomatic hypertrophic cardiomyopathy

Impaired hyperemic myocardial blood flow (MBF) in hypertrophic cardiomyopathy (HCM), despite normal epicardial coronary arteries, results in microvascular dysfunction. The aim of the present study was to determine the relative contribution of extravascular compressive forces to microvascular dysfunction in HCM. Eighteen patients with symptomatic HCM and normal coronary arteries and 10 age-matched healthy volunteers were studied with PET to quantify resting and hyperemic MBF at a subendocardial and subepicardial level. In HCM patients, MRI was performed to determine left ventricular (LV) mass index (LVMI) and volumes, echocardiography to assess diastolic perfusion time, heart catheterization to measure LV outflow tract gradient (LVOTG) and LV pressures, and serum NH(2)-terminal pro-brain natriuretic peptide (NT-proBNP) as a biochemical marker of LV wall stress. Hyperemic MBF was blunted in HCM vs. controls (2.26 +/- 0.97 vs. 2.93 +/- 0.64 ml min(-1) g(-1), P < 0.05). In contrast to controls (1.38 +/- 0.15 to 1.25 +/- 0.19, P = not significant), the endocardial-to-epicardial MBF ratio decreased significantly in HCM during hyperemia (1.20 +/- 0.11 to 0.88 +/- 0.18, P < 0.01). This pattern was similar for hypertrophied septum and lateral wall. Hyperemic MBF was inversely correlated with LVOTG, NT-proBNP, left atrial volume index, and LVMI (all P < 0.01). Multivariate regression analysis, however, revealed that only LVMI and NT-proBNP were independently related to hyperemic MBF, with greater impact at the subendocardial myocardial layer. Hyperemic MBF is more severely impaired at the subendocardial level in HCM patients. The level of impairment is related to markers of increased hemodynamic LV loading conditions and LV mass. These observations suggest that, in addition to reduced capillary density caused by hypertrophy, extravascular compressive forces contribute to microvascular dysfunction in HCM patients.

DEFEAT heart failure: clinical manifestations, diagnostic assessment, and etiology of geriatric heart failure

Aging is characterized by heterogeneity, both in health and in disease. Older adults who have heart failure (HF) often have atypical and delayed clinical manifestations and many have diastolic HF. The assessment and management of HF in older adults may be simplified by a 5-step process called DEFEAT HF: (1) establish a clinical Diagnosis of HF; (2) establish an Etiology for HF, preferably in collaboration with a cardiologist; (3) determine Fluid status and achieve euvolemia; (4) determine left ventricular Ejection frAction; and (5) provide evidence-based Therapy.

Valvular Aortic Stenosis in the Elderly

Elderly patients with valvular aortic stenosis have an increased prevalence of coronary risk factors, of coronary artery disease, and evidence of other atherosclerotic vascular diseases. Statins may reduce the progression of aortic stenosis (AS). Angina pectoris, syncope or near syncope, and congestive heart failure are the 3 classic manifestations of severe AS. Prolonged duration and late peaking of an aortic systolic ejection murmur best differentiate severe AS from mild AS on physical examination. Doppler echocardiography is used to diagnose the prevalence and severity of AS. The indications for cardiac catheterization and the medical management of AS are discussed. Once symptoms develop, aortic valve replacement (AVR) should be performed in patients with severe or moderate AS. Other indications for AVR are discussed. Warfarin should be administered indefinitely after AVR in patients with a mechanical aortic valve and in patients with a bioprosthetic aortic valve who have either atrial fibrillation, prior thromboembolism, left ventricular systolic dysfunction, or a hypercoagulable condition. Patients with a bioprosthetic aortic valve without any of these 4 risk factors should be treated with aspirin 75-100 mg daily.

Will 3-dimensional PET-CT enable the routine quantification of myocardial blood flow?

Quantification of myocardial blood flow (MBF) and flow reserve has been used extensively with positron emission tomography (PET) to investigate the functional significance of coronary artery disease. Increasingly, flow quantification is being applied to investigations of microvascular dysfunction in early atherosclerosis and in nonatherosclerotic microvascular disease associated with primary and secondary cardiomyopathies. Fully three-dimensional (3D) acquisition is becoming the standard imaging mode on new equipment, bringing with it certain challenges for cardiac PET, but also the potential for MBF to be measured simultaneously with routine electrocardiography (ECG)-gated perfusion imaging. Existing 3D versus 2D comparative studies support the use of 3D cardiac PET for flow quantification, and these protocols can be translated to PET-CT, which offers a virtually noise-free attenuation correction. This technology combines the strengths of cardiac CT for evaluation of anatomy with cardiac PET for quantification of the hemodynamic impact on the myocardium. High throughput clinical imaging protocols are needed to evaluate the incremental diagnostic and prognostic value of this technology.

Recovery of Left Ventricular Systolic Longitudinal Strain After Valve Replacement in Aortic Stenosis and Relation to Natriuretic Peptides

OBJECTIVE

We sought to examine left ventricular (LV) longitudinal systolic myocardial contractility in isolated valvular aortic stenosis (AS) before and after valve replacement and relation to natriuretic peptides.

METHODS

In all, 45 patients with symptomatic AS without significant coronary artery disease were studied by serial tissue Doppler echocardiography and analysis of plasma atrial and brain natriuretic peptide (Nt-pro-BNP).

RESULTS

LV myocardial systolic strain was significantly reduced in AS with preserved ejection fraction and most pronounced in patients with advanced heart failure symptoms. Nt-pro-BNP was significantly related to LV mass index and mean LV strain (r = 0.63, P < .001; and r = 0.61, P < .001, respectively). Mean myocardial systolic strain increased after valve replacement (baseline -9 +/- 4% vs -14 +/- 4% at 12 months, P < .001). The increase of systolic strain and the observed regression of LV mass index were independently related to changes of Nt-pro-BNP (r = -0.67, P < .001; and r = -0.71, P < .001, respectively) during 12 months of follow-up after valve replacement. A significant association was found between changes of plasma atrial natriuretic peptide and echocardiographic markers of LV diastolic function.

CONCLUSION

LV longitudinal systolic strain is severely depressed despite preserved LV ejection fraction and fractional shortening in AS. A significant association exists among natriuretic peptides, myocardial longitudinal contractility, and the degree of symptoms. Reverse LV remodeling after aortic valve replacement with regression of myocardial hypertrophy results in improvement of LV longitudinal myocardial strain and decrease of Nt-pro-BNP plasma levels. LV strain analysis might have the potential to identify patients with asymptomatic AS who might benefit from earlier surgical intervention to preserve overall LV function.

Effect of chronic afterload increase on left ventricular myocardial function in patients with congenital left-sided obstructive lesions

The effect of pressure-overloading distance on left ventricular (LV) function in patients with congenital aortic coarctation and aortic stenosis (AS) was investigated. LV long-axis motions were recorded using M-mode and tissue Doppler imaging (TDI) techniques in 46 consecutive patients with severe LV outflow tract obstruction (23 coarctation and 23 AS), and results were compared with those of 23 controls. TDI lateral and septal long-axis systolic velocities, early diastolic velocities, and M-mode systolic amplitudes were lower in patients with coarctation and AS than controls (lateral site long-axis systolic velocity 7.1 +/- 1.7 and 6.4 +/- 1.6 vs 9.7 +/- 1.7 cm/s, septal site long-axis systolic velocity 6.3 +/- 1.3 and 5.4 +/- 1.1 vs 7.7 +/- 1.3 cm/s; lateral site early diastolic velocity 10.5 +/- 2.2 and 8.2 +/- 2.6 vs 13.1 +/- 2.5 cm/s, septal site early diastolic velocity 7.4 +/- 1.9 and 6.0 +/- 1.8 vs 10.8 +/- 1.6 cm/s, lateral site M-mode systolic amplitude 1.4 +/- 0.2 and 1.3 +/- 0.2 vs 1.6 +/- 0.2 cm, septal site M-mode systolic amplitude 1.2 +/- 0.2 and 1.1 +/- 0.2 vs 1.4 +/- 0.2 cm, p <0.01 for all). Compared with patients with coarctation, those with AS had lower TDI velocities, higher early LV filling velocity/long-axis diastolic velocity ratios, and a higher prevalence of long-axis incoordination (p <0.05 for all) despite similar LV mass index, ejection fraction, and systolic wall stress. In conclusion, LV long-axis function is impaired in patients with a chronic increase in afterload. Worse deterioration in LV function and higher prevalence of long-axis incoordination independent of LV outflow resistance is seen in patients with proximally increased LV afterload (AS) compared with distal disease (aortic coarctation).

Strain rate imaging differentiates hypertensive cardiac hypertrophy from physiologic cardiac hypertrophy (athlete's heart)

BACKGROUND

This study sought to determine whether strain rate imaging could distinguish between individuals with hypertensive left ventricular hypertrophy (LVH) and those with strength-training athletic LVH.

METHODS

In all, 108 participants (30 hypertensive LVH, 30 strength-training LVH, 48 control) were enrolled. In addition to a baseline echocardiogram, strain, peak systolic strain rate (SR(S)), peak early diastolic strain rate (SR(E)), and peak late diastolic strain rate values were compared in the apical 4-chamber view.

RESULTS

Athletes had no significant differences in strain, SR(S), SR(E), or peak late diastolic strain rate compared with control subjects (P = .11, .99, .85, and .09, respectively). Individuals with hypertensive LVH had significantly decreased strain, SR(S), and SR(E) (-16.8 +/- 3.2%, -0.99 +/- 0.15 s(-1), and 1.54 +/- 0.40 s(-1), respectively) compared with control subjects (-21.7 +/- 3.5%, -1.31 +/- 0.27 s(-1), and 2.35 +/- 0.57 s(-1), respectively; all P < .0001).

CONCLUSION

Hypertensive LVH has significant longitudinal strain, SR(S), and SR(E) reductions versus control. The lack of these reductions in athletes suggests that strain rate imaging may have clinical use in discerning the physiologic LVH state.

Clinical manifestations, diagnostic assessment, and etiology of heart failure in older adults

Aging is characterized by heterogeneity, both in health and in dis-ease. Older adults who have heart failure (HF) often have a typical and delayed clinical manifestations and many have diastolic HF. The assessment and management of HF in older adults may be simplified by a 5-step process called DEFEAT HF: (1) Establish a clinical Diagnosis of HF; (2) Establish an Etiology for HF, preferably in collaboration with a cardiologist; (3) Determine Fluid status and achieve euvolemia; (4) Determine left ventricular Ejection frAction; and (5) Provide evidence-based Therapy.

Aortic valve replacement for aortic stenosis is associated with improved aortic distensibility at long-term follow-up

BACKGROUND

Aortic valve stenosis (AS) is the most frequent form of valvular heart disease. The number of studies evaluating the effect of aortic valve replacement (AVR) for AS on aortic vascular function is limited. The aim of the present study was to examine alterations in aortic distensibility in patients with AS during a 1-year follow-up after AVR.

METHODS

Twelve patients with severe AS who underwent AVR were prospectively examined (mean age 65 +/- 11 years, 7 men). Systolic and diastolic ascending aortic diameters (SD and DD, respectively) were recorded in M mode 3 cm above the aortic valve from a parasternal long-axis view. The SD and DD were measured at the time of maximum anterior motion of the aorta and at the start of the QRS complex, respectively. Aortic stiffness index (beta) was defined as [ln(SBP/DBP)] x DD/deltaD, where ln is the natural logarithm, SBP and DBP are the systolic and diastolic blood pressure values, respectively, and deltaD = SD - DD.

RESULTS

As expected, aortic stenosis severity and left ventricular mass decreased significantly after AVR. Aortic diameter changes (systolic minus diastolic dimensions) progressively increased and the aortic stiffness index progressively improved to levels comparable with those of age-, sex-, and risk factor-matched controls at the 1-year assessment.

CONCLUSIONS

Aortic valve replacement in patients with AS is associated with a progressive improvement in aortic distensibility to 1-year values similar to those of controls.

Exercise Testing in Asymptomatic Aortic Stenosis

AIMS

To determine the safety of exercise testing (ET) in patients with moderate or severe asymptomatic aortic stenosis (AAS) and its accuracy to predict the need for surgery and mortality.

METHODS

106 consecutive patients with AAS performed a maximal ET.

RESULTS

Follow-up [10.7 (4.9-19.4) months (percentile 25-75)] was completed in 102 patients (96.2%), 63.9 years (+/-15.1), 65 (61.3%) male, peak gradient 82.8 mm Hg (+/-25.4), mean gradient 50.5 mm Hg (+/-16.6), valve area 0.67 cm(2) (+/-0.16); 67 patients (65.7%) had abnormal ET. Among the 35 patients with normal ET, there were no deaths and 10 aortic valve replacements (AVR) (28.5%) were performed. Among the 67 patients with abnormal ET, 37 (55.2%) had events (35 AVR and 2 died) (p <0.0001). There were no complications with ET.

CONCLUSION

ET may be performed safely in patients with AAS. ET gives additional information to an AVR decision.

Is the coronary flow velocity reserve improvement after aortic valve replacement for aortic stenosis transient? Results of a 3-year follow-up

The coronary flow velocity reserve (CFR) is decreased in patients with aortic valve stenosis (AS). The aim of the present prospective study was to examine the CFR in AS patients with normal epicardial coronary arteries during a 3-year follow-up of aortic valve replacement (AVR). A total of 30 AS patients (17 women and 13 men) were enrolled in this prospective follow-up study; they all had a normal coronary angiogram and underwent dipyridamole stress transesophageal echocardiography (STEE) for CFR measurement before AVR. Nine of them participated in this 3-year follow-up study, and all patients were examined 16 months and 3 years after AVR by STEE. The CFR of AS patients was decreased before AVR. Different extents of diastolic coronary flow velocity reduction (resting and posthyperaemic) were observed resulting in a significant CFR improvement, despite the low number of patients during the 16-month follow-up. A further posthyperaemic flow velocity reduction was demonstrated after the 3-year follow-up, resulting in a significant CFR impairment. The CFR decreased in 5 cases, but remained practically unchanged in 3 after the first CFR measurement; only the CFR of 1 patient improved minimally. The main finding of the current study is that the CFR improvement 16 months after AVR, which paralleled the regression of the left ventricular hypertrophy, was found to be transient. Coronary flow velocity reserve impairment was demonstrated after the long-term (3-year) follow-up in most of the patients, which could not be explained by extravascular compressive forces.

Coronary and peripheral blood flow changes following biventricular pacing and their relation to heart failure improvement

AIMS

To study the effect of cardiac resynchronization therapy (CRT) on coronary and peripheral arterial circulation and to assess whether their changes are related to the improvement in patients' functional capacity and prognostically important biochemical markers.

METHODS AND RESULTS

Twenty-five patients were studied (New York Heart Association classes III and IV, left ventricular ejection fraction <35%, QRS>120 ms, mean age 66 +/- 2.1 years). Coronary blood flow (CBF), forearm blood flow (FBF), and their reserve were measured by transoesophageal echocardiography (in cm/s) and venous occlusion plethysmography (in mL/100 mL/min) at baseline and following 3 months of CRT. N-terminal-pro-brain natriuretic peptide (Nt-pro-BNP) and serum adhesion molecules, sICAM-1 and sVCAM-1 levels were also assessed. CRT induced a non-significant increase in resting CBF (baseline vs. CRT: 52.1 +/- 5.5 vs. 58.2 +/- 3.6, P: NS), whereas hyperaemic CBF was increased by CRT (baseline vs. CRT: 67.8 +/- 6.8 vs. 79.8 +/- 6.2, P < 0.05). Significant increases were observed in resting FBF (baseline vs. CRT: 1.6 +/- 0.2 vs. 2.6 +/- 0.2, P < 0.05) and hyperaemic FBF (baseline vs. CRT: 2.1 +/- 0.2 vs. 3.2 +/- 0.3, P < 0.05). The per cent difference in hyperaemic FBF was related to the per cent change in Nt-pro-BNP (r = -0.71, P < 0.05) and the per cent improvement in exercise duration (r = 0.80, P < 0.05).

CONCLUSION

CRT induces favourable changes in coronary and peripheral arterial function. Changes in peripheral blood flow are related to patients' improvement and may be prognostically significant.

Analytical modeling of the instantaneous maximal transvalvular pressure gradient in aortic stenosis

In presence of aortic stenosis, a jet is produced downstream of the aortic valve annulus during systole. The vena contracta corresponds to the location where the cross-sectional area of the flow jet is minimal. The maximal transvalvular pressure gradient (TPG(max)) is the difference between the static pressure in the left ventricle and that in the vena contracta. TPG(max) is highly time-dependent over systole and is known to depend upon the transvalvular flow rate, the effective orifice area (EOA) of the aortic valve and the cross-sectional area of the left ventricular outflow tract. However, it is still unclear how these parameters modify the TPG(max) waveform. We thus derived an explicit analytical model to describe the instantaneous TPG(max) across the aortic valve during systole. This theoretical model was validated with in vivo experiments obtained in 19 pigs with supravalvular aortic stenosis. Instantaneous TPG(max) was measured by catheter and its waveform was compared with the one determined from the derived equation. Our results showed a very good concordance between the measured and predicted instantaneous TPG(max). Total relative error and mean absolute error were on average 9.4+/-4.9% and 2.1+/-1.1 mmHg, respectively. The analytical model proposed and validated in this study provides new insight into the behaviour of the TPG(max) and thus of the aortic pressure at the level of vena contracta. Because the static pressure at the coronary inlet is similar to that at the vena contracta, the proposed equation will permit to further examine the impact of aortic stenosis on coronary blood flow.

Value of 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) gated SPECT for the detection of silent myocardial ischemia in hemodialysis patients: clinical variables associated with abnormal test results

BACKGROUND

Although coronary artery disease is a major cause of mortality and morbidity in patients undergoing hemodialysis, there is no accurate diagnostic strategy for these patients.

AIM

To assess the value of 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) gated single-photon emission computed tomography for the detection of silent myocardial ischemia in patients undergoing hemodialysis and to evaluate the clinical variables associated with abnormal test results.

METHODS

Thirty-one asymptomatic patients undergoing hemodialysis (20 men, 11 women), with a mean age of 45 years (range, 25-75 years), were included in the study. Serum electrolytes, creatinine, homocysteine and adhesion molecules were measured prior to dialysis. Ambulatory blood pressure, carotid intima-media thickness measurements, echocardiography and stress 99mTc-MIBI imaging were performed in all patients, whereas coronary angiography was performed only in patients with abnormal myocardial perfusion scintigraphy and/or echocardiography.

RESULTS

Gated myocardial perfusion scintigraphy results were abnormal in nine patients (29%) and coronary angiography was abnormal in six patients. After a median follow-up of 20 months (range, 14-28 months), nine patients experienced a cardiac event. Seven of the nine patients (78%) with abnormal myocardial perfusion scintigraphy suffered a cardiac event, compared with only two of 22 patients (9%) with normal myocardial perfusion scintigraphy (P<0.0001). Patients with abnormal perfusion scintigraphy had higher serum C-reactive protein, homocysteine and adhesion molecule levels and the duration of hemodialysis was significantly longer.

CONCLUSION

In asymptomatic hemodialysis patients, gated myocardial perfusion scintigraphy is a safe and non-invasive screening technique for the detection of coronary artery disease and for predicting future cardiac events. The presence of ischemia correlates significantly with markers of inflammation. The discordant results (abnormal myocardial perfusion scintigraphy/normal coronary angiography) can be attributed to angiographically unrecognized occult atherosclerotic changes and abnormal vasodilatation capacity of the coronary circulation.

Coronary microvascular dysfunction in male patients with Anderson-Fabry disease and the effect of treatment with alpha galactosidase A

OBJECTIVE

To measure coronary flow reserve (CFR), an index of microvascular function, in Anderson-Fabry disease (AFD) at baseline and after enzyme replacement therapy (ERT).

METHODS AND RESULTS

Mean (SD) myocardial blood flow (MBF) at rest and during hyperaemia (adenosine 140 microg/kg/min) was measured in 10 male, non-smoking patients (53.8 (10.9) years, cholesterol 5.5 (1.3) mmol/l) and in 24 age matched male, non-smoking controls (52.0 (7.6) years, cholesterol 4.5 (0.6) mmol/l) by positron emission tomography (PET). Resting and hyperaemic MBF and CFR (hyperaemic/resting MBF) were reduced in patients compared with controls (0.99 (0.17) v 1.17 (0.25) ml/g/min, p < 0.05; 1.37 (0.32) v 3.44 (0.78) ml/g/min, p < 0.0001; and 1.41 (0.39) v 3.03 (0.85), p < 0.0001, respectively). This coronary microvascular dysfunction was independent of cholesterol concentrations. PET was repeated in five patients after 10.1 (2.3) months of ERT; resting and hyperaemic MBF and CFR were unchanged after ERT (0.99 (0.16) v 0.99 (0.16) ml/g/min; 1.56 (0.29) v 1.71 (0.3) ml/g/min; and 1.6 (0.37) v 1.74 (0.28), respectively; all not significant).

CONCLUSIONS

The results of the present study show that patients with AFD have very abnormal coronary microvascular function. These preliminary data suggest that ERT has no effect on coronary microvascular dysfunction. Further work is necessary to determine whether treatment at an earlier stage in the course of the disease may improve coronary microvascular function in patients with AFD.

The non-invasive documentation of coronary microcirculation impairment: role of transthoracic echocardiography

Transthoracic Doppler echocardiographic-derived coronary flow reserve is an useful hemodynamic index to assess dysfunction of coronary microcirculation. Isolated coronary microvascular abnormalities are overt by reduced coronary flow reserve despite normal epicardial coronary arteries. These abnormalities may occur in several diseases (arterial hypertension, diabetes mellitus, hypercholesterolemia, syndrome X, aortic valve disease, hypertrophic cardiomyopathy and idiopathic dilated cardiomyopathy). The prognostic role of impaired microvascular coronary flow reserve has been shown unfavourable especially in hypertrophic or idiopathic dilated cardiomyopathies. Coronary flow reserve reduction may be reversible, for instance after regression of left ventricular hypertrophy subsequent to valve replacement in patients with aortic stenosis, after anti-hypertensive treatment or using cholesterol lowering drugs. Coronary flow reserve may increase by 30% or more after pharmacological therapy and achieve normal level >3.0. In contrast to other non invasive tools as positron emission tomography, very expensive and associated with radiation exposure, transthoracic Doppler-derived coronary flow reserve is equally non invasive but cheaper, very accessible and prone to a reliable exploration of coronary microvascular territories, otherwise not detectable by invasive coronary angiography, able to visualize only large epicardial arteries.

Impaired coronary and myocardial flow in severe aortic stenosis is associated with increased apoptosis: a transthoracic Doppler and myocardial contrast echocardiography study

OBJECTIVE

To test the hypothesis that impaired coronary and myocardial blood flow are linked with increased myocyte apoptosis, thus establishing a link between pressure overload and left ventricular (LV) remodelling.

METHODS AND RESULTS

Peak diastolic coronary blood flow velocity (CBFV) was evaluated at transthoracic Doppler echocardiography, and signal intensity (SI) and the rate of SI rise (beta) were measured at myocardial contrast echocardiography in 11 patients with severe aortic stenosis and LV hypertrophy. In the same patients, biopsies were obtained from the anterolateral LV free wall during surgery and analysed for cardiomyocyte apoptosis. LV mass corrected CBFV (CBFVI) was significantly lower in patients than in controls (median 0.100 cm.g/s (interquartile range 0.07-0.115) v 0.130 cm.g/s (0.130-0.160), p = 0.002). Similarly, SI*beta was significantly lower in patients than in controls (11 1/s (8-66) v 83 1/s (73-95), p = 0.001). Apoptotic rate was increased in aortic stenosis more than 100-fold versus controls (1.2% (0.8-1.4) v 0.01% (0.01-0.01), p < 0.001) and inversely correlated with lower CBFVI and SI*beta (r = -0.77, p = 0.001 for both).

CONCLUSIONS

Patients with severe aortic stenosis and LV hypertrophy have impaired myocardial perfusion, which is associated with enhanced cardiomyocyte apoptosis. Impaired myocardial perfusion and the ensuing oxygen demand-supply imbalance may, at least partially, be responsible for increased apoptosis and possible transition to heart failure, thus establishing a link between pressure overload, LV remodelling, and heart failure.

Usefulness of the exercise electrocardiogram in diagnosing ischemic or coronary heart disease in patients with chest pain

We compared exercise electrocardiograms with myocardial perfusion images and coronary angiograms in 186 patients who had been referred to coronary angiography for stable angina pectoris. All had normal electrocardiographic findings at rest, and none had undergone coronary revascularization. Sensitivity, specificity, and positive and negative predictive values with the exercise electrocardiogram for prediction of reversible and/or irreversible hypoperfusion were 58%, 89%, 76%, and 77% and 70%, 88%, 72%, and 87%, respectively, for prediction of reversibility only. Corresponding values for comparison with coronary angiography were 65%, 89%, 74%, and 83%, respectively. Sensitivities were considerably lower in women than in men. Exercise electrocardiographic findings were normal in 50% of women and 25% of men who had reversible perfusion defects.

Effect of left ventricular assist device combination therapy on myocardial blood flow in patients with end-stage dilated cardiomyopathy

BACKGROUND

Changes in myocardial blood flow (MBF) and coronary flow reserve (CFR) are independent prognostic risk factors in idiopathic dilated cardiomyopathy (DCM). The aim of this study was to assess the impact of left ventricular unloading using left ventricular assist device (LVAD) combination therapy on resting MBF and CFR in patients with end-stage heart disease.

METHODS

We studied 11 patients with deteriorating end-stage DCM (New York Heart Association Class 4) treated with LVAD support combined with pharmacologic therapy in a recovery program. Absolute MBF was measured using oxygen-15-labeled water (H(2)(15)O) positron emission tomography (PET) at rest during LVAD support and 15 minutes after the LVAD was switched off. Data were corrected for rate pressure product (RPP) when appropriate. Hyperemic MBF (intravenous adenosine, 140 mug/kg . min) was also measured in 6 patients with the LVAD switched off. CFR was calculated as the ratio MBF adenosine/MBF LVAD off (corrected). Data are expressed as mean +/- SD.

RESULTS

At 317 +/- 193 days after device implantation, resting MBF was 0.95 +/- 0.29 (LVAD on) and 1.46 +/- 0.62 (LVAD off, corrected) ml/min . g (p = 0.01). MBF (LVAD on) was comparable with that of 11 age- and gender-matched normal controls (1.09 +/- 0.22 ml/min . g). CFR in the LVAD group was 1.49 +/- 0.99 compared with 3.56 +/- 1.42 in normal controls (p < 0.01).

CONCLUSIONS

During LVAD support, resting MBF (LVAD on) was comparable to MBF in normal controls and increased when the LVAD was switched off. However, CFR was significantly impaired, even though all patients studied showed varying degrees of myocardial recovery. The implications of these findings, particularly in the long term, require further study.

Loss of endothelial KATP channel-dependent, NO-mediated dilation of endocardial resistance coronary arteries in pigs with left ventricular hypertrophy

The influence of left ventricular hypertrophy (LVH) on the endothelial function of resistance endocardial arteries is not well established. The aim of this study was to characterise the mechanisms responsible for UK-14,304 (alpha(2)-adrenoreceptor agonist)-induced endothelium-dependent dilation in pig endocardial arteries isolated from hearts with or without LVH. LVH was induced by aortic banding 2 months before determining endothelial function. Following euthanasia, hearts were harvested and endocardial resistance arteries were isolated and pressurised to 100 mmHg in no-flow conditions. Vessels were preconstricted with acetylcholine (ACh) or high external K(+) (40 mmol l(-1) KCl). Results are expressed as mean+/-s.e.m. UK-14,304 induced a maximal dilation representing 79+/-6% (n=8) of the maximal diameter. NO synthase (l-NNA, 10 micromol l(-1), n=7) or guanylate cyclase (ODQ, 10 micromol l(-1), n=4) inhibition reduced (P<0.05) UK-14,304-dependent dilation to 35+/-6 and 18+/-7%, respectively. Apamin and charybdotoxin reduced (P<0.05) to 39+/-8% (n=4) the dilation induced by UK-14,304. In depolarised conditions, however, this dilation was prevented (P<0.05). UK-14,304-induced dilation was reduced (P<0.05) by glibenclamide (Glib, 1 micromol l(-1)), a K(ATP) channel blocker, either alone (35+/-10%, n=5) or in combination with l-NNA (34+/-9%, n=4). In LVH, UK-14,304-induced maximal dilation was markedly reduced (25+/-4%, P<0.05) compared to control; it was insensitive to l-NNA (21+/-5%) but prevented either by the combination of l-NNA, apamin and charybdotoxin, or by 40 mmol l(-1) KCl. Activation of endothelial alpha(2)-adrenoreceptor induces an endothelium-dependent dilation of pig endocardial resistance arteries. This dilation is in part dependent on NO, the release of which appears to be dependent on the activation of endothelial K(ATP) channels. This mechanism is blunted in LVH, leading to a profound reduction in UK-14,304-dependent dilation.

Coronary flow reserve in the newborn lamb: an intracoronary Doppler guide wire study

Recent studies indicate a severely reduced coronary flow reserve (CFR) in neonates with congenital heart disease. The significance of these studies remains debatable, as the ability of the anatomically normal neonatal heart to increase coronary flow is currently unknown. This study was designed to establish normal values for CFR in newborns after administration of adenosine [pharmacologic CFR (pCFR)] and as induced by acute hypoxemia (reactive CFR). Thirteen mechanically ventilated newborn lambs were studied. Coronary flow velocities were measured in the proximal left anterior descending coronary artery before and after adenosine injection (140 and 280 microg/kg i.v.) using an intracoronary 0.014-in Doppler flow-wire. Measurements were made at normal oxygen saturation (SaO(2)) and during progressive hypoxemia induced by lowering the fraction of inspired oxygen. CFR was defined as the ratio of hyperemic to basal average peak flow velocity. In a hemodynamically stable situation with normal SaO(2), pCFR was 3.0 +/- 0.5. pCFR decreased with increasing hypoxemia. Regression analysis showed a linear relation between SaO(2) and pCFR (R = 0.86, p < 0.0001). Reactive CFR obtained at severe hypoxemia (Sao(2) <30%) was 4.2 +/- 0.8, and no significant further increase in coronary flow velocity occurred by administration of adenosine. Newborn lambs have a similar capacity to increase coronary flow in response to both pharmacologic and reactive stimuli as older subjects. Administration of adenosine does not reveal the full capacity of the newborn coronary circulation to increase flow, however, as the flow increase caused by severe hypoxemia is significantly more pronounced.

Myocardial protection with intermittent cold blood during aortic valve operation: antegrade versus retrograde delivery

BACKGROUND

Intermittent antegrade cold blood cardioplegia is superior to warm blood cardioplegia in patients who have aortic valve operation. This study compared the cardioprotective efficacy of intermittent antegrade and retrograde cold blood cardioplegia with emphasis on metabolic stress in the left and right ventricles.

METHODS

Thirty-nine patients who had elective aortic valve replacement were prospectively randomly selected to receive intermittent antegrade or retrograde cold blood cardioplegia. Left and right ventricular biopsies were collected 5 minutes after institution of cardiopulmonary bypass and 20 minutes after cross-clamp removal and were used to determine metabolic changes. Metabolites (adenine nucleotides, amino acids, and lactate) were measured using high-powered liquid chromatography and enzymatic techniques. Serial measurement of troponin I release was also used as a marker of myocardial injury.

RESULTS

Preoperative characteristics were similar between groups. There was no in-hospital mortality, and no differences were observed in postoperative complications. Preischemic concentration of taurine was significantly higher in left ventricular biopsies, whereas adenosine triphosphate tended to be lower in the left ventricle. At reperfusion adenosine triphosphate levels were significantly lower than preischemic levels in right but not left ventricles irrespective of the route of delivery. The alanine-glutamate ratio was significantly elevated in both ventricles. Myocardial injury as assessed by troponin I release was also significantly increased in both groups.

CONCLUSIONS

Retrograde and antegrade intermittent cold blood cardioplegic techniques are associated with suboptimal myocardial protection. Metabolic stress was more pronounced in the right than the left ventricle irrespective of the cardioplegic route of delivery used.

Coronary microvascular dysfunction and prognosis in hypertrophic cardiomyopathy

BACKGROUND

Microvascular dysfunction, reflected by an inadequate increase in myocardial blood flow in response to dipyridamole infusion, is a recognized feature of hypertrophic cardiomyopathy. Its long-term effect on the prognosis is unknown. We prospectively evaluated a cohort of patients with hypertrophic cardiomyopathy after they had undergone quantitative assessment of myocardial blood flow by positron-emission tomography (PET).

METHODS

Fifty-one patients (New York Heart Association class I or II) were followed for a mean (+/-SD) of 8.1+/-2.1 years after PET. Twelve subjects with atypical chest pain served as controls. Measurement of flow was performed at base line and after the infusion of the coronary vasodilator dipyridamole, with the use of nitrogen-13-labeled ammonia. Patients were then divided into three equal groups with increasing values of myocardial blood flow.

RESULTS

The response of myocardial blood flow to dipyridamole was severely blunted in the patients, as compared with the controls (1.50+/-0.69 vs. 2.71+/-0.94 ml per minute per gram of tissue, P<0.001). Sixteen patients (31 percent) had an unfavorable outcome (death from cardiovascular causes, progression to New York Heart Association class III or IV, or sustained ventricular arrhythmias requiring the implantation of a cardioverter-defibrillator) 2.2 to 9.1 years after PET. Reduced blood flow in response to dipyridamole was strongly associated with an unfavorable outcome. Multivariate analysis showed that among patients in the lowest of the three flow groups the age-adjusted relative hazard of death from cardiovascular causes was 9.6 (P=0.02) and the relative hazard of an unfavorable outcome (a combined end point) was 20.1 (P=0.003), as compared with patients in the two other flow groups. Specifically, all four patients who died from heart failure and three of five who died suddenly were in this subgroup.

CONCLUSIONS

In patients with hypertrophic cardiomyopathy, the degree of microvascular dysfunction is a strong, independent predictor of clinical deterioration and death. Severe microvascular dysfunction is often present in patients with mild or no symptoms and may precede clinical deterioration by years.

Myocardial perfusion imaging by magnetic resonance imaging

In the diagnosis and treatment of patients with suspected or known coronary artery disease, noninvasive methodologies for assessing myocardial perfusion have been invaluable. Clinically, nuclear techniques such as single photon emission tomography thallium and sestamibi have predominated. They are limited, however, by the radiation burden, relatively poor spatial resolution, and attenuation artifact caused by soft tissue. In contrast, magnetic resonance imaging (MRI) is notable for its anatomic detail, sharp tissue contrast, excellent spatial and temporal resolution, versatility, and lack of ionizing radiation. It is therefore a potentially attractive alternative to nuclear imaging for the assessment of myocardial perfusion. This review summarizes the principles of MRI myocardial perfusion measurement, discusses recent clinical applications, and highlights future developments in the field.