Coronary flow dynamics and reserve assessed by transesophageal echocardiography in obstructive hypertrophic cardiomyopathy

Flow velocity quantification by exploiting the principles of the Doppler effect and magnetic particle imaging

Changes in blood flow velocity play a crucial role during pathogenesis and progression of cardiovascular diseases. Imaging techniques capable of assessing flow velocities are clinically applied but are often not accurate, quantitative, and reliable enough to assess fine changes indicating the early onset of diseases and their conversion into a symptomatic stage. Magnetic particle imaging (MPI) promises to overcome these limitations. Existing MPI-based techniques perform velocity estimation on the reconstructed images, which restricts the measurable velocity range. Therefore, we developed a novel velocity quantification method by adapting the Doppler principle to MPI. Our method exploits the velocity-dependent frequency shift caused by a tracer motion-induced modulation of the emitted signal. The fundamental theory of our method is deduced and validated by simulations and measurements of moving phantoms. Overall, our method enables robust velocity quantification within milliseconds, with high accuracy, no radiation risk, no depth-dependency, and extended range compared to existing MPI-based velocity quantification techniques, highlighting the potential of our method as future medical application.

The prognostic role of myocardial strain indices and dipyridamole stress test in renal transplantation patients

INTRODUCTION

Renal transplantation (RT) increases survival in end-stage kidney disease patients but cardiovascular diseases remain the leading cause of morbidity and mortality. We evaluated the role of myocardial strain (2DSTE) indices and dipyridamole-induced (DIPSE) changes in echocardiographic parameters at baseline for the prediction of clinical events and echocardiographically assessed deterioration of cardiac function in a RT population.

METHODS

Forty-five RT patients underwent an echocardiographic study at baseline including 2DSTE and DIPSE. If no cardiovascular/renal event occurred, patients were investigated at 3-year follow-up; eight patients presented a clinical event while 37 patients were re-evaluated.

RESULTS

Coronary flow reserve (CFR) was abnormal in 24% of the population. DIPSE induced improvements in classic and 2DSTE systolic and diastolic echocardiographic indices including TWIST, UNTWIST, global longitudinal strain (GLS), and circumferential strain (P < .05 for all). Compared to baseline, deteriorations in E/E', LVEF, E', and TWIST were observed at follow-up (P < .05 for all). DIPSE-induced changes in GLS, global radial strain, and LVEF were associated with changes in these indices at follow-up (P < .05 for all). Higher LV mass index, E/E', and lower MAPSE, E', and CFR at baseline were associated with the occurrence of clinical events at follow-up (P < .05 for all).

CONCLUSIONS

In RT patients, coronary vascular dysfunction (ie, low CFR) was associated with the occurrence of adverse events. DIPSE-induced changes in myocardial strain and classic echocardiographic indices could identify individuals with a subclinical deterioration in cardiac function at follow-up. This may indicate that DIPSE could serve as a means to assess myocardial reserve in this population.

[Vascular functional alterations in hypertrophic cardiomyopathy]

Hypertrophic cardiomyopathy is a hereditary, not uncommon cardiac disease, which is associated with asymmetric thickening and hypertrophy of the interventricular septum unrelated to hemodynamic reasons. Despite hypertrophic cardiomyopathy is considered to be a disorder of the heart muscle, several associated vascular alterations have been described. The aim of the present review is to summarize vascular functional alterations in hypertrophic cardiomyopathy.

Regional difference of microcirculation in patients with asymmetric hypertrophic cardiomyopathy: transthoracic Doppler coronary flow velocity reserve analysis

OBJECTIVE

To evaluate, by noninvasive coronary flow velocity reserve (CFVR), whether patients with asymmetric hypertrophic cardiomyopathy (HC), with or without left ventricular outflow tract obstruction, demonstrate significant regional differences of CFVR.

METHODS

We evaluated 61 patients with HC (27 men; mean age 49 ± 16 years), including 20 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 41 patients without obstruction (HCM). The control group included 20 age- and sex-matched subjects. Transthoracic Doppler echocardiography CFVR of the left anterior descending coronary artery (LAD) and the posterior descending coronary artery (PD) were performed, including calculation of relative CFVR as the ratio between CFVR LAD and CFVR PD.

RESULTS

Compared with the controls, all the patients with HC had lower CFVR LAD (2.12 ± 0.53 vs 3.34 ± 0.67; P < .001) and CFVR PD (2.29 ± 0.49 vs 3.21 ± 0.65; P < .001). CFVR LAD in HOCM group in comparison with the HCM group was significantly lower (1.93 ± 0.42 vs 2.22 ± 0.55; P = .047), due to higher basal diastolic coronary flow velocities (0.40 ± 0.09 vs 0.33 ± 0.07 m/sec; P = .002), with similar hyperemic diastolic flow velocities (0.71 ± 0.16 vs 0.76 ± 0.19 m/sec; P = .330), respectively. There was no significant difference in CFVR PD between patients with HOCM and those with HCM (2.33 ± 0.46 vs 2.27 ± 0.50; P = .636), respectively. Relative CFVR was lower in the HOCM group compared with the HCM group (0.84 ± 0.16 vs 0.98 ± 0.14; P = .001). By multivariable regression analysis, left ventricular outflow tract gradient was the independent predictor of CFVR LAD (B = -0.24; P = .008) and relative CFVR (B = -0.34; P = .016).

CONCLUSIONS

CFVR LAD and relative CFVR were significantly lower in patients with HOCM compared with patients with HCM. Regional differences of CFVR are present only in patients with significant left ventricular outflow tract obstruction, which suggests that obstruction per se, by increasing wall stress in basal conditions, leads to higher basal diastolic coronary flow velocities and results in lower CFVR in LAD compared with PD.

Long-term prognostic value of coronary flow velocity reserve in patients with hypertrophic cardiomyopathy: 9-year follow-up results from SZEGED study

Reduction in coronary flow velocity reserve (CFR) is a recognized feature in hypertrophic cardiomyopathy (HCM). We sought to assess the long-term prognostic value of CFR by pulsed-wave Doppler transesophageal echocardiography (TEE) in HCM patients. The study comprised 20 patients with typical features of HCM. The patients were enrolled in 1999. All patients underwent a standard transthoracic echo-Doppler study to evaluate left ventricular function and a stress vasodilator TEE study to evaluate CFR. The success rate of follow-up was 18 out of 20 (90%). During a mean follow-up of 90 +/- 24 months, four patients suffered cardiovascular death (2 sudden cardiac deaths and 2 strokes). The other seven patients underwent invasive procedures (coronary angiography, implantable cardioverter defibrillator implantation, percutaneous transluminal septal myocardial ablation) or showed cerebrovascular events. Using receiver operator characteristic analysis, CFR < 2.35 was a significant predictor for cardiovascular event-free survival (sensitivity 91%, specificity 71%, area under the curve 74%, P = 0.05). Multivariable regression analysis showed that only CFR (hazard ratio (HR) 4.21, P < 0.05) was an independent predictor of cardiovascular event-free survival. Despite the relatively small number of patients involved in the study, results could suggest that CFR should be considered as an independent predictor for future cardiovascular events in HCM patients. However, further studies with larger HCM patient populations are warranted.

Assessment of intravascular and extravascular mechanisms of myocardial perfusion abnormalities in obstructive hypertrophic cardiomyopathy by myocardial contrast echocardiography

OBJECTIVES

To assess mechanisms of myocardial perfusion impairment in patients with hypertrophic cardiomyopathy (HCM).

METHODS

Fourteen patients with obstructive HCM (mean (SD) age 53 (10) years, 11 men) underwent intravenous adenosine myocardial contrast echocardiography (MCE), positron emission tomography (PET) and cardiac catheterisation. Fourteen healthy volunteers (mean age 31 (4) years, 11 men) served as controls. Relative myocardial blood volume (rBV), exchange flow velocity (beta), myocardial blood flow (MBF), MBF reserve (MFR) and endocardial-to-subepicardial (endo-to-epi) MBF ratio were measured from the steady state and contrast replenishment time-intensity curves.

RESULTS

Patients with HCM had lower rest MBF (for LVRPP-corrected)--mean (SD) (0.92 (0.12) vs 1.13 (0.25) ml/min/g, p<0.01)--and hyperaemic MBF--(2.56 (0.49) vs 4.34 (0.78) ml/min/g, p<0.01) than controls. Resting rBV was lower in patients with HCM (0.094 (0.016) vs 0.138 (0.014) ml/ml), and during hyperaemia (0.104 (0.018) ml/ml vs 0.185 (0.024) ml/ml) (all p<0.001) than in controls. beta tended to be higher in HCM at rest (9.4 (4.6) vs 7.7 (4.2) ml/min) and during hyperaemia (25.8 (6.4) vs 23.1 (6.2) ml/min) than in controls. Septal endo-to-epi MBF decreased during hyperaemia (0.86 (0.15) to 0.64 (0.18), p<0.01). rBV was inversely correlated with left ventricular (LV) mass index (p<0.05). Both hyperaemic and endo-to-epi MBF were inversely correlated with LV end-diastolic pressure, LV mass index, and LV outflow tract pressure gradient (all p<0.05). MCE-derived MBF correlated well with PET at rest (r = 0.84) and hyperaemia (r = 0.87) (all p<0.001).

CONCLUSIONS

In patients with HCM, LV end-diastolic pressure, LV outflow tract pressure gradient, and LV mass index are independent predictors of rBV and hyperaemic MBF.

Coronary flow velocity reserve in hypertensive patients with left ventricular systolic dysfunction

BACKGROUND

Hypertensive microvascular disease is speculated to be a limiting factor for the ability of left ventricular (LV) hypertrophy to maintain LV systolic function in systemic hypertension. The role of coronary reserve, which may be affected by microvascular disease, remains uncertain in the pathophysiology of hypertensive heart disease.

HYPOTHESIS

A progressive impairment of coronary flow velocity reserve (CFVR) according to the presence and severity of LV systolic dysfunction is anticipated to occur in hypertension.

METHODS

According to the absence or presence of LV dysfunction (LV fractional shortening - FS% < 30), two groups of hypertensive patients were investigated: HP1 (n = 9, FS% = 36+/-6) and HP2 (n = 13, FS% = 18+/-6). Eight normal subjects (NL) served as controls (LVFS% = 35+/-3). Doppler blood flow velocity was obtained from the left anterior descending coronary artery using transesophageal echocardiography before, and during 6-min continuous adenosine infusion (140 microg x kg(-1) x min(-1) intravenous). The CFVR was calculated as the ratio of maximal to baseline peak diastolic flow velocities.

RESULTS

The comparison among NL, HP1, and HP2 groups showed statistically different (p < 0.05) mass index (101+/-18, 172+/-46, and 257+/-54 g x m(-2)), end-systolic wall stress (76.9+/-14.4, 78.4+/-23.9, and 174.5+/-43.0 10(3) x dyn x cm(-2)), and CFVR (3.5+/-0.6, 3.2+/-0.4, and 2.6+/-0.8), respectively. The CFVR correlated significantly and directly with LVFS% (r = 0.40) and correlated inversely with both mass index (r = -0.54) and end-systolic stress (r = -0.40).

CONCLUSIONS

These results indicate that CFVR impairment is weakly related to LV dysfunction in hypertension.

Comparison of diastolic septal perforator flow velocities in hypertrophic cardiomyopathy versus hypertensive left ventricular hypertrophy

In this study, we measured diastolic septal perforator flow velocities by Doppler transthoracic echocardiography (TTE) in patients with hypertrophic cardiomyopathy (HCM). Using color-guided pulsed Doppler TTE, septal perforator flow velocity recordings were attempted in 69 patients and successfully recorded in 47 (68%). First, we compared 14 patients with HCM to 12 controls and to 11 patients with hypertension with left ventricular hypertrophy. Next, in 10 additional patients with HCM, we compared the septal velocities with the epicardial left anterior descending artery (LAD) velocities recorded during the same TTE study. In the patients with HCM, the peak septal diastolic velocities were twice that of the normal controls (88 +/- 40 vs 41 +/- 13 cm/s) and also higher than in hypertensive left ventricular hypertrophy (51 +/- 18 cm/s, p < 0.0001). All 10 patients with HCM showed a step-up of peak diastolic velocity from the LAD to the septal perforator from 41 +/- 9 to 72 +/- 17 cm/s (p < 0.0001). Three patients with HCM had surgical septal myectomy. These patients had luminal narrowings of the small intramural arteries at histopathologic examination. In conclusion, pulsed Doppler measurement of septal perforator flow velocities is feasible. In HCM, the epicardial coronary arteries enlarge to accommodate increased flow, and diastolic velocity is normalized. In contrast, the increased velocities in the septal branches of patients with HCM are similar to those previously observed in tunnel-like obstructions. These findings suggest that in HCM, notwithstanding an increase in coronary flow, hemodynamically significant narrowings are present in the septal branches. Doppler TTE may become useful for evaluation of abnormal intramural coronary flow in HCM.

Relation between peripheral vascular endothelial function and coronary flow reserve in patients with chest pain and normal coronary angiogram

To evaluate the relation between peripheral vascular endothelial function and coronary flow reserve (CFR), we assessed flow mediated dilation (FMD) of brachial artery and the intima-media thickness (IMT) of the carotid artery in 32 subjects (mean age 58+/-9 years, M/F=9:23 ) with chest pain and normal coronary angiogram. The subjects were divided into 2 groups according to CFR >or=2.1 or <2.1 measured with transthoracic echocardiography in distal left anterior descending coronary artery. We found % FMD was decreased in the group with CFR <2.1 than those of CFR >or=2.1 and CFR was correlated with peripheral FMD. However, IMT was not different between two groups. These results suggest that microvascular dysfunction is primarily related to endothelial dysfunction rather than advanced atherosclerosis and because it is a generalized process that involves the whole arteries, the measurement of brachial FMD can be a useful diagnostic tool to evaluate microvascular dysfunction in patients with chest pain and normal coronary angiogram.

Effect of one or more co-morbid conditions on diagnostic accuracy of coronary flow velocity reserve for detecting significant left anterior descending coronary stenosis

OBJECTIVE

To determine the effect of one or multiple co-morbid conditions on the diagnostic accuracy of coronary flow velocity reserve (CFVR) in a heterogeneous patient population.

METHODS

CFVR was measured in the left anterior descending coronary artery (LAD) by transthoracic Doppler echocardiography (TTDE) in 318 consecutive patients before elective coronary angiography. CFVR was calculated as the average peak diastolic velocity during intravenous ATP infusion divided by baseline flow velocity. All patients underwent coronary angiography within 48 hours. Significant LAD stenosis was defined as > 50% luminal narrowing. Diagnostic accuracy of CFVR was analysed according to the type and number of risk factors that may adversely affect microvascular function.

RESULTS

CFVR was measured in 309 patients, of whom 105 were found to have significant LAD stenosis based on coronary angiography. CFVR < 2.0 had a sensitivity of 86% and a specificity of 77% for predicting significant LAD stenosis. Left ventricular hypertrophy (LVH) was the only factor that significantly lowered diagnostic accuracy (61% with LVH v 84% without LVH, p < 0.001). Diagnostic accuracy was not affected by increasing number of risk factors.

CONCLUSIONS

The diagnostic accuracy of CFVR by TTDE for detecting significant LAD stenosis remains high in a more clinically relevant population with multiple cardiovascular co-morbidities. Only the presence of LVH adversely affected diagnostic accuracy.

Pattern of exercise-induced ST change is related to coronary flow reserve in patients with chest pain and normal coronary angiogram

OBJECTIVE

To evaluate the usefulness of exercise treadmill test in determining the true microvasculature-induced ischemia, we compared the pattern of ST depression with coronary flow reserve (CFR) using transthoracic Doppler echocardiography (TTE) in patients with chest pain and normal coronary angiogram.

DESIGN

Fifty-nine subjects (M/F=21:38, mean age 55+/-9 years) with chest pain and normal coronary angiogram underwent maximal symptom-limited exercise treadmill test (ETT). CFR was estimated with TTE and dipyridamole. Patients with a history of acute myocardial infarction, regional wall motion abnormalities, hypertrophic cardiomyopathy, ejection fraction less than 50%, or primary valvular heart disease were excluded from this study.

RESULTS

No ST change was observed in 20 of 59 (34%) patients, up slope depression was observed in 20 (34%), flat depression in 13 (22%), and down slope depression in 6 (10%). Eleven of thirty nine (28%) exercise positive patients had decreased CFR <2.1. CFR was 3.1+/-0.6 in group with no ST change, 3.1+/-0.6 in group with up slope depression, 2.1+/-0.6 in group with flat depression (p<0.05 versus group with no change and group with upslope depression, respectively), and 2.0+/-0.4 in group with down slope depression (p<0.05 versus group with no change and group with up slope depression, respectively). Flat to down slope depression of ST change during ETT had sensitivity of 58% and specificity of 95% for predicting CFR <2.1.

CONCLUSION

Flat and down slope depression of ST segment during ETT might increase the sensitivity and specificity to detect the true microvasculature-induced ischemia that is defined as CFR less than 2.1 in patients with chest pain and normal coronary angiogram.

The imbalance between coronary reserve and wall stress explains the severity of ventricular dysfunction in hypertension

BACKGROUND

The pathophysiologic role of coronary reserve impairment in hypertensive cardiac dysfunction is still debated. Previously, we demonstrated that satisfactory coronary vasodilatation may coexist with ventricular systolic dysfunction. It is conceivable that coronary reserve might otherwise be inappropriate for enhanced myocardial oxygen demand and may thus affect cardiac performance negatively.

HYPOTHESIS

Myocardial supply-demand imbalance contributes to the severity of ventricular dysfunction in hypertension (HTN).

METHODS

Fractional shortening (%) and end-systolic stress (10(3) x dyn x cm(-2)) were determined using echocardiography, and coronary reserve was calculated using transesophageal Doppler echocardiography. Coronary reserve/stress (cm2 x dyn(-1)) was utilized as a measure of supply-demand. Groups NL (20 healthy subjects), HTN1 (15 patients, fractional shortening > or = 30), HTN2 (19 patients, 20 < or = fractional shortening < 30), and HTN3 (21 patients, fractional shortening < 20) were constituted.

RESULTS

Compared with NL and HTN1, groups HTN2 and HTN3 had significantly (p < 0.05) greater end-systolic stress (NL = 72 +/- 16, HTN1 = 72 +/- 23, HTN2 = 143 +/- 32, HTN3 = 186 +/- 70). Coronary reserve was impaired in HTN3 alone (NL = 3.5 +/- 0.6, HTN1 = 3.4 +/- 1.0, HTN2 = 3.1 +/- 1.0, HTN3 = 2.6 +/- 1.1), but coronary reserve/stress was reduced in both HTN2 and HTN3 (NL = 50 +/- 12, HTN1 = 53 +/- 21, HTN2 = 22 +/- 7, HTN3 = 15 +/- 7). Stepwise regression analysis identified diastolic internal dimension, end-systolic stress, and coronary reserve/stress as independently associated with fractional shortening.

CONCLUSION

The imbalance between supply-demand explains the severity of hypertensive cardiac dysfunction and adds information to cardiac enlargement and elevated wall stress.

Relation between Duke treadmill score and coronary flow reserve using transesophageal Doppler echocardiography in patients with microvascular angina

OBJECTIVES

The link between coronary flow reserve (CFR) and Duke treadmill score (DTS) in patients with microvascular angina remains elusive.

METHODS

We studied 108 subjects (M/F=48:60, mean age 54+/-9 years) with chest pain and normal coronary angiogram. ETT was performed by Bruce's protocol and the equation for calculating DTS was DTS=exercise duration-(5x ST deviation)-(4x exercise angina), with 0=none, 1=nonlimiting, 2=exercise limiting. The coronary flow velocity at diastole (PDV) using transesophageal Doppler echocardiography (TEE) was obtained from the proximal left anterior descending coronary artery and CFR was calculated as the ratio of hyperemic PDV after the intravenous infusion of dipyridamole (0.56 mg/kg) to baseline PDV.

RESULTS

CFR was 3.04+/-0.45 in group with negative ETT and 2.19+/-0.62 in group with positive ETT (P<0.001) and was 1.51+/-0.31 in high risk group with a score of < or = -11, 2.39+/-0.63 in moderate risk group with scores between -11 and + 5, and 3.04+/-0.43 in low risk group with a score of > or = +5 on DTS (P<0.001 versus low risk group, respectively). DTS has significant correlation with CFR (r=0.704, P<0.001).

CONCLUSIONS

DTS is a composite index that reflects CFR and helps clinicians determine the severity of ischemia in patients with microvascular angina.

Comparison of Coronary Flow Velocities Between Patients with Obstructive and Nonobstructive Type Hypertrophic Cardiomyopathy: Noninvasive Assessment by Transthoracic Doppler Echocardiography

BACKGROUND

We aimed to compare coronary flow velocity (CFV) measurements of patients with nonobstructive (NHCM) and obstructive hypertrophic cardiomyopathy (HOCM) by using transthoracic Doppler echocardiography (TTDE).

METHODS AND RESULTS

In 11 patients with NHCM and 26 with HOCM, CFV in the distal left anterior descending (LAD) coronary was measured by TTDE (3.5 MHz) under the guidance of color Doppler flow mapping in addition to standard 2D and Doppler echocardiography. The results were compared with 24 normal participants who had no evidence of cardiac disease. Peak diastolic velocity of LAD was also higher in NHCM and HOCM than controls (52 +/- 14 cm/sec and 54 +/- 20 cm/sec vs 41 +/- 11 cm/sec, respectively, P < 0.01). The analysis of systolic velocities revealed abnormal flow patterns in 16 (61%) patients with HOCM (12 systolic-reversal flow and 4 no systolic flow) and 6 (54%) (5 reversal flow and 1 zero flow) patients with NHCM (-11 +/- 30 cm/sec and -13 +/- 38 cm/sec, vs 24 +/- 9 cm/sec, respectively, P < 0.001). Linear regression analysis demonstrated no correlation between intraventricular pressure gradient and coronary flow velocities in HOCM patients. However, there were significant positive and negative correlations between septal thickness and diastolic and systolic velocities, respectively (r = 0.50, P < 0.002, and r =-0.43, P < 0.005).

CONCLUSION

We conclude that the coronary flow velocity abnormalities are independent from the type of hypertrophic cardiomyopathy.

Measurement of coronary vasomotor function: getting to the heart of the matter in cardiovascular research

Measurement of endothelial function in patients has emerged as a useful tool for cardiovascular research. Although no gold standard for the measurement of endothelial function exists, the measurement of flow-mediated dilation in the brachial artery, assessed with Doppler ultrasonography, is the most studied method. However, the assumption that endothelial dysfunction detected in brachial arteries is a manifestation of systemic endothelial dysfunction including the coronary circulation may not be entirely valid. Brachial and myocardial circulations differ in terms of the microvascular architecture, the pattern of blood flow and vascular resistance (e.g. shunt vessels occur in the hand but not in the myocardium), their metabolic regulation, type of receptors that contribute to humoral regulation and the pathways that are activated to induce hyperaemia. In this context, measuring coronary vasomotor function may be more useful than brachial artery measures to predict and assess potential myocardial damage related to limited vascular responsiveness. This review aims to provide an overview of the basic concept of coronary flow reserve and its different modalities of measurement, as well as its utility in cardiovascular research.

Coronary hemodynamics in patients with symptomatic hypertrophic cardiomyopathy

The purpose of this study was to analyze coronary hemodynamics and determine a possible mechanism for microvascular dysfunction in patients with symptomatic hypertrophic cardiomyopathy (HC). Although patients with HC have been shown to have microvascular dysfunction and reduced coronary flow reserve (CFR), the mechanism by which this occurs is not well understood. We studied coronary hemodynamics in 8 patients with symptomatic HC and compared them with 8 matched controls. Compared with controls, patients with HC had higher coronary blood flow, lower coronary resistance, and lower CFR. Patients with HC also had abnormal phasic coronary flow characteristics. These results suggest that the reduction of CFR in patients with HC may be secondary to near maximal vasodilation of the microcirculation in the basal state.

Determinants of coronary flow abnormalities in obstructive type hypertrophic cardiomyopathy: noninvasive assessment by transthoracic Doppler echocardiography

We aimed to visualize the coronary flow velocities (CFV) of patients with hypertrophic obstructive cardiomyopathy by using transthoracic Doppler echocardiography, and to determine the relationship between abnormal CFV patterns and conventional echocardiography indices. Guided by 2-dimensional echocardiography and Doppler color flow mapping, CFV in the distal left anterior descending coronary artery were measured in 21 patients with hypertrophic obstructive cardiomyopathy using a 3.5-MHz transducer. The results were compared with those of 18 control subjects. Abnormal systolic flow patterns were observed in 15 (71%) patients (11 systolic-reversal flow and 4 no systolic flow). For patients and control subjects, peak diastolic velocity and velocity-time integral obtained from distal left anterior descending coronary artery were higher (63 +/- 21 cm/s and 18.5 +/- 4 cm vs 41 +/- 11 cm/s and 14.2 +/- 5 cm, respectively; P <.01 for both) whereas peak systolic velocity and velocity-time integral were significantly lower (-17 +/- 10 cm/s and 4.5 +/- 6 cm vs 24 +/- 9 cm/s and 9.5 +/- 4 cm, respectively; P <.001 for both). Significant positive and negative correlations between diastolic CFV and septal thickness index (r = 0.79, P <.0001), and between systolic CFV and septal thickness index (r = -0.65, P <.005), have been observed. CFV abnormalities that could easily be recorded by a standard Doppler echocardiographic study seem to be related to septal thickness rather than the degree of obstruction in hypertrophic obstructive cardiomyopathy.

Coronary Flow Reserve after Coronary Intervention is Similar in Patients with Preserved Viability in Previous Myocardial Infarction and in Those with Angina Pectoris

The relationship between coronary flow reserve (CFR) and viability in the infarcted myocardium has not been fully clarified. We measured coronary blood flow velocity immediately after coronary intervention (with percutaneous transluminal coronary angioplasty [PTCA] or stenting) in 38 patients with previous myocardial infarction and preserved viability and 48 with angina pectoris. CFR was calculated and was similar between the two patient groups. No differences in the incidence of post-intervention CFR > 2.0 were detected; there were no differences in postintervention CFR between patients with preserved myocardial viability and those with angina pectoris who underwent PTCA. Coronary stenting reduced the percentage diameter stenosis in both groups compared with PTCA and slightly increased the post-intervention CFR. No differences were, however, detected in postintervention CFR between patients with preserved myocardial viability and those with angina pectoris who underwent additional stenting. These results reveal that in patients with preserved myocardial viability, post-intervention CFR was restored to values similar to those in patients with angina pectoris.

First-pass MR imaging in the assessment of perfusion impairment in patients with hypertrophic cardiomyopathy and the Asp175Asn mutation of the alpha-tropomyosin gene

PURPOSE

To assess first-pass magnetic resonance (MR) imaging in the evaluation of perfusion impairment in a genetically homogeneous population of patients with hypertrophic cardiomyopathy (HCM) and the Asp175Asn mutation of the alpha-tropomyosin gene and to evaluate the association between hypertrophy and perfusion.

MATERIALS AND METHODS

Rest-stress first-pass MR imaging with gadopentetate dimeglumine was performed in 17 patients with HCM and the Asp175Asn substitution in the alpha-tropomyosin gene and in five control subjects. Global and segmental first-pass reserve index (FPR) measurements were derived from signal intensity versus time curves. Left ventricular (LV) wall thickness and LV mass index were measured on cine MR images. The Mann-Whitney test was used to evaluate the difference in FPR between the patient group and the control group. The Spearman correlation was used to evaluate the association between LV hypertrophy and FPR.

RESULTS

Global FPR was significantly lower in the patients with HCM than in the control subjects (1.12 +/- 0.35 vs 1.80 +/- 0.58, P =.015). In patients with HCM, maximal LV wall thickness and LV mass index correlated negatively with global FPR (r = -0.723, P =.001 and r = -0.598, P =.011, respectively). At the regional level, segmental FPR correlated inversely with LV wall thickness (r = -0.389; P <.001) in patients with HCM.

CONCLUSION

First-pass MR imaging facilitates global and regional evaluation of perfusion impairment in patients with HCM. The severity of perfusion impairment is associated with the degree of LV hypertrophy.

Physiologic assessment of coronary artery stenosis by coronary flow reserve measurements with transthoracic Doppler echocardiography: comparison with exercise thallium-201 single piston emission computed tomography

OBJECTIVES

We evaluated the value of coronary flow reserve (CFR), as determined by transthoracic Doppler echocardiography (TTDE), for physiologic assessment of coronary artery stenosis severity, and we compared TTDE measurements with those obtained by exercise thallium-201 (Tl-201) single-photon emission computed tomography (SPECT).

BACKGROUND

Coronary flow reserve measurements by TTDE have been reported to be useful for assessing angiographic left anterior descending coronary artery (LAD) stenosis. However, discrepancies exist between angiographic and physiologic estimates of coronary lesion severity.

METHODS

We studied 36 patients suspected of having coronary artery disease. The flow velocity in the distal LAD was measured by TTDE both at rest and during intravenous infusion of adenosine. Coronary flow reserve was calculated as the ratio of hyperemic to basal peak (peak CFR) and mean (mean CFR) diastolic flow velocities. The CFR measurements by TTDE were compared with the results of Tl-201-SPECT.

RESULTS

Complete TTDE data were acquired for 33 of 36 study patients. Of these 33 patients, Tl-201-SPECT confirmed reversible perfusion defects in the LAD territories in 12 patients (group A). Twenty-one patients had normal perfusion in the LAD territories (group B). Peak CFR and mean CFR (mean value +/- SD) were 1.5 +/- 0.6 and 1.5 +/- 0.7 in group A and 2.8 +/- 0.8 and 2.7 +/- 0.7 in group B, respectively. Both peak and mean CFR < or = 2.0 predicted reversible perfusion defects, with a sensitivity and specificity of 92% and 90%, respectively.

CONCLUSIONS

Noninvasive measurement of CFR by TTDE provides data equivalent to those obtained by Tl-201-SPECT for physiologic estimation of the severity of LAD stenosis.

Transesophageal echocardiography (TEE) in the evaluation of the coronary arteries

With technical advancements, including high frequency, multiplane transducers, digital acquisition and display, and left-sided contrast agents, TEE is emerging as a promising method for evaluating coronary artery disease. Visualization of proximal coronary artery stenoses and coronary artery anomalies is already possible. Research studies using TEE measurement have contributed to understanding coronary artery physiology and may prove to be a valuable clinical tool in the future.

Assessment of coronary flow reserve with transthoracic Doppler echocardiography: comparison among adenosine, standard-dose dipyridamole, and high-dose dipyridamole

Coronary flow reserve (CFR), defined as a ratio of hyperemic-to-basal coronary flow velocity, provides important information about the functional aspect of coronary circulation. However, it usually is determined by invasive methods during catheterization. Recent studies have shown that transthoracic Doppler echocardiography (TTDE) may be useful in the measurement of coronary flow velocity in the distal portion of the left anterior descending coronary artery (LAD). The vasodilators used for hyperemia are adenosine and dipyridamole. However, the coronary vasodilative response and systemic hemodynamic effects of the two agents have not been directly compared with TTDE. We assessed blood flow velocity and vascular resistance in the distal LAD by TTDE during an intravenous 2-minute adenosine infusion (140 microg/kg/min) and low- (0.56 mg/kg) and high-dose dipyridamole (0. 84 mg/kg) infusion in 25 patients with patent LAD. Coronary flow velocity was successfully recorded in 20 patients (80%) during baseline and the consecutive vasodilator-infusion period. Compared with low-dose dipyridamole, adenosine infusion induced a higher CFR (3.7 +/- 0.87 vs 2.73 +/- 0.65; P <.05) and a lower coronary resistance index (0.31 +/- 0.04 vs 0.35 +/- 0.08; P <.05). But by increasing the dipyridamole dose to 0.84 mg/kg, the values of the CFR and coronary resistance index became comparable to those of adenosine infusion (2.85 +/- 0.78 vs 3.03 +/- 0.7, P = not significant [NS]; 0.33 +/- 0.04 vs 0.32 +/- 0.09, P = NS; respectively). We conclude that adenosine seems to be a favorable vasodilator for the measurement of CFR with TTDE.

Effect of verapamil on systolic and diastolic coronary blood flow velocity in asymptomatic and mildly symptomatic patients with hypertrophic cardiomyopathy

OBJECTIVE

To assess non-invasively the effect of verapamil treatment on coronary blood flow velocity in asymptomatic and mildly symptomatic patients with hypertrophic cardiomyopathy.

DESIGN

High frequency transthoracic Doppler echocardiography was used to compare resting phasic coronary blood flow velocity before and after a one month period of verapamil treatment in 17 patients (14 men and three women) with non-obstructive hypertrophic cardiomyopathy. Eighteen healthy subjects formed an age and sex matched control group. Systolic and diastolic coronary blood flow velocity was measured in the distal portion of left anterior descending coronary artery using high frequency transthoracic Doppler echocardiography. Blood flow velocity before and after verapamil was compared in the patients with cardiomyopathy and with the results in the control group.

RESULTS

Compared with the controls, patients with hypertrophic cardiomyopathy had increased diastolic coronary blood flow velocity (41.8 (8.1) v 59.9 (21.9) cm/s, p < 0.01) and a lower mean systolic coronary blood flow velocity (18.7 (10.8) v -11.2 (27.5) cm/s, p < 0. 01) before verapamil treatment. A backward pattern of systolic flow, manifested by negative values of coronary blood flow velocity, was recorded in eight of the patients, while no negative values were found in the controls. After verapamil treatment the retrograde systolic blood flow was restored to an anterograde pattern in only one patient. The mean value of systolic coronary blood flow velocity did not change significantly and remained lower than the systolic forward flow velocity in the controls (-3.6 (31.8) v 18.7 (10.8) cm/s, p < 0.05). However, diastolic coronary blood flow velocity decreased significantly after verapamil (59.9 (21.9) v 50.7 (19.5) cm/s p < 0.05), reaching a level comparable with that in the controls (50.7 (19.5) v 41.8 (8.1) cm/s, p > 0.05).

CONCLUSIONS

In contrast to healthy subjects, in non-obstructive hypertrophic cardiomyopathy the systolic pattern of coronary blood flow was heterogeneous (both retrograde and anterograde), and diastolic coronary blood flow velocity was abnormally increased, despite a lack of significant symptoms. Verapamil treatment did not restore the forward pattern of systolic blood flow but decreased diastolic blood flow velocity to a level comparable with that in healthy subjects.

Coronary flow reserve of normal left anterior descending artery in patients with ischemic heart disease: A transesophageal Doppler study

The aim of this study was to investigate the flow reserve of a normal left anterior descending coronary artery (LAD) in patients with coronary artery disease (CAD) of other epicardial vessels by Doppler transesophageal echocardiography (TEE). Thirty-one consecutive patients (age 59 +/- 8 years; 23 men) referred for TEE were considered. Eighteen patients had CAD and a 70% or greater LAD stenosis (group 1); 13 patients had right and/or circumflex CAD (>/=70% stenosis) and normal or minimally diseased LAD (group 2). Ten patients (age 54 +/- 11 years) with normal coronary arteries constituted group 3. Baseline and adenosine (0.160 microg/kg per minute intravenously over 60 minutes) flow velocities in the LAD were measured by pulsed Doppler examination during TEE. Peak and mean systolic and diastolic flow velocities were calculated. Adenosine/baseline peak and mean velocity ratios were used for evaluating blood flow reserve in the LAD. Heart rate and arterial pressure values were similar in the 3 groups at baseline and during adenosine infusion. Baseline and adenosine-related flow velocities were comparable in the 3 groups. Peak and mean diastolic velocity ratios were lower in groups 1 and 2 compared with group 3 (peak velocity ratio 1.68 +/- 0.81 and 1.93 +/- 0.35 vs 2.62 +/- 0.32, P <. 05; mean velocity ratio 1.71 +/- 0.86 and 2.01 +/- 0.41 vs 2.84 +/- 0.74, P <.05), whereas no differences were found between groups 1 and 2. No significant differences were found in systolic flow velocity ratios among the 3 groups. Patients with ischemic heart disease have a reduced diastolic flow velocity reserve in the LAD independent from the presence of significant LAD stenosis. Thus the adenosine TEE-Doppler study should be considered a screening test for CAD rather than for LAD disease.

Contrast-enhanced transthoracic second harmonic echo Doppler with adenosine: a noninvasive, rapid and effective method for coronary flow reserve assessment

OBJECTIVES

The purpose of this study is to evaluate the feasibility in detecting blood flow in the left anterior descending coronary artery (LAD) using transthoracic color Doppler (CD) imaging (in both second harmonic and fundamental mode) along with contrast enhancement and to verify if this new noninvasive method along with adenosine is safe, rapid and effective in assessing coronary flow reserve (CFR).

BACKGROUND

Feasibility of contrast-enhanced transthoracic Doppler recording (in both second harmonic and fundamental mode) of blood flow velocity in the LAD has not been assessed. Adenosine has a greater vasodilator potency and more favorable kinetics than dipyridamole and thus it can be more suitable for assessing CFR in conjunction with this method.

METHODS

Sixty-one patients with angiographically patent LAD underwent CD (both in fundamental and harmonic mode) as well as color-guided pulsed wave (PW) Doppler recording of blood flow velocity in the distal LAD before and after intravenous contrast injection. A second group of patients (n = 77), undergoing coronary angiography, was submitted to transthoracic contrast-enhanced PW Doppler recording of blood flow velocity in the LAD using harmonic CD as a guide, at rest and during adenosine-induced hyperemia.

RESULTS

Harmonic CD along with echo contrast consistently improved blood flow detection in the LAD; the success rate in detecting flow of optimal quality was 88% with this approach, whereas it was 11% and 16% with CD in fundamental mode, respectively, before and after contrast. Pulsed wave Doppler results paralleled those of harmonic CD (p < 0.001 contrast harmonic vs. fundamental). In the second group of patients coronary angiography revealed 0% to <40% stenosis in 24 patients (group I), > or =40% to < or =75% in 17 patients (group II) and >75% stenosis in 34 patients (group III). There was a significant difference in CFR among the three groups of patients; CFR for peak diastolic velocity was (mean +/- SD): 2.88+/-0.7 (group I), 2.09+/-0.5 (group II) and 1.51+/-0.5 cm/s (group II) (p < 0.05 group I vs. both group II and group III; p < 0.05 group II vs. group III). The whole examination took less than 10 min.

CONCLUSIONS

Contrast-enhanced second harmonic Doppler recording of blood velocity in the LAD is highly feasible and in combination with adenosine it is a rapid, safe and effective method for assessing CFR ratio.

Abnormal coronary flow profiles at rest and during rapid atrial pacing in patients with hypertrophic cardiomyopathy

To examine the mechanism of myocardial ischemia in hypertrophic cardiomyopathy (HCM), coronary flow velocity was measured in the left anterior descending coronary artery (LAD) using a Doppler guide wire in 11 patients with HCM and in 8 normal controls. The average peak velocity (APV), percent increase of APV (%APV), and APV during systole (Vs) and diastole (Vd) were calculated at rest and during rapid atrial pacing. The APV in HCM reached a peak value at a heart rate of 90 beats/min, while in the controls the APV increased continuously until the heart rate reached 130 beats/min [%APV (130 beats/min); 103+/-30% in HCM vs 139+/-23% in controls, p<0.04]. During rapid atrial pacing, Vs in the controls increased, whereas Vs in HCM decreased further. During high-rate pacing, Vd in HCM reached a peak value at a heart rate of 90 beats/min, whereas in the controls, Vd increased continuously until the heart rate reached 130 beats/min. The acceleration rate of early diastolic flow was significantly lower in HCM than in the controls (1.85+/-0.66 vs 3.18+/-1.62 m/s2, p<0.03). This abnormal response might be due to an increase in the reverse systolic flow and a decrease in the diastolic flow, probably caused by a slow acceleration of early diastolic flow velocity in the LAD.

Hypertrophic cardiomyopathy: MR measurement of coronary blood flow and vasodilator flow reserve in patients and healthy subjects

PURPOSE

To evaluate coronary blood flow per gram of myocardial mass and vasodilator flow reserve in patients with hypertrophic cardiomyopathy (HCM) and in healthy subjects by using breath-hold velocity-encoded cine (VEC) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Twenty-nine patients with HCM and nine healthy volunteers were examined. Fast VEC MR images were obtained in an oblique imaging plane perpendicular to the coronary sinus before and after intravenous injection of dipyridamole (0.56 mg/kg). The products of mean velocity and cross-sectional area of the vessel were integrated to measure blood flow. Breath-hold cine MR images encompassing the entire left ventricle were acquired to quantify the left ventricular mass.

RESULTS

In the basal state, the coronary blood flow per gram of myocardial mass was 0.74 mL/min/g +/- 0.23 in healthy subjects and 0.62 mL/min/g +/- 0.27 in patients with HCM. After administration of dipyridamole, coronary blood flow in patients with HCM increased to a level significantly less than that in healthy subjects (1.03 mL/min/g +/- 0.40 vs 2.14 mL/min/g +/- 0.51; P < .01), resulting in a severely depressed flow reserve ratio in patients with HCM compared with that in healthy subjects (1.72 +/- 0.49 vs 3.01 +/- 0.75; P < .01).

CONCLUSION

Breath-hold VEC MR imaging is a noninvasive technique for evaluating coronary flow per gram of myocardial mass and coronary flow reserve.

Current concepts of coronary flow reserve for clinical decision making during cardiac catheterization

Measurements of coronary flow reserve, once used only for research, have gained wide acceptance as an additional diagnostic approach in the decision-making process of diagnostic cardiac catheterization and coronary interventions. Apart from the noninvasive determination of coronary flow reserve, intracoronary Doppler flow wires have facilitated decision making in the catheterization laboratory. Different techniques, unstandardized procedures, and data from uncomparable patient populations have remained a confounding factor. This review examines current concepts of coronary flow reserve as well as methodologic considerations and pitfalls. Applications of coronary flow reserve for periinterventional assessment are evaluated on the background of practical guidance. According to a detailed examination of arterial structure and function, a normal coronary flow reserve exceeds a value of 3.0. Values below 3.0 suggest involvement of microvascular disease caused by functional or structural alterations. The influences of various factors such as age, hemodynamics, hypercholesterolemia, hypertrophy, hypertension, syndrome X, and coronary artery disease are discussed in relation to the effect on coronary flow reserve. From available information, measurements of coronary flow reserve are an adjunct to current interventional technology to optimize individual patient care. Further efforts should be undertaken to incorporate these new methods into our routine clinical decision making.

Characteristics of coronary flow velocity in constrictive pericarditis

A 50-yr-old man developed constrictive pericarditis following an episode of acute pericarditis. Cardiac catheterization revealed a typical early diastolic dip and plateau configuration in both the right and left ventricular pressure curves. The coronary flow velocity pattern determined using an intracoronary Doppler guidewire showed an abrupt decrease in peak velocity at early diastole and followed by plateau until late diastole, the so-called dip and plateau configuration. After a successful pericardiectomy, cardiac catheterization no longer showed the dip and plateau configuration, but the early diastolic dip in the coronary flow velocity persisted probably because of infiltration of the organic involvement into the myocardium.

Alterations of the architecture of subendocardial arterioles in patients with hypertrophic cardiomyopathy and impaired coronary vasodilator reserve: a possible cause for myocardial ischemia

OBJECTIVES

The study was designed to investigate the architecture of subendocardial arterioles of patients with hypertrophic cardiomyopathy (HCM) and angina pectoris with respect to coronary vasodilator reserve.

BACKGROUND

There is growing evidence that the coronary microvasculature is abnormal in HCM. Arterioles, which mainly regulate intramyocardial blood flow, are especially suspect.

METHODS

Thirteen patients with HCM (50.1+/-12.6 years old, mean value +/- SD) were studied after exclusion of any relevant coronary stenoses. Subendocardial arterioles (density [n/mm2], wall area [microm2], percent lumen area [%lumen], periarteriolar collagen area [microm2]), myocyte diameter (microm) and interstitial collagen fraction (Vv%) were evaluated by means of stereologic morphometry of transvenous biopsy samples. Coronary blood flow was measured quantitatively with the inert chromatographic argon method at basal conditions and after dipyridamole (0.5 mg/kg body weight over 4 min intravenously), and coronary vasodilator reserve was calculated as the ratio of coronary resistance at basal conditions and after pharmacologic vasodilation. Data from five normotensive subjects (45.4+/-11 years old, p = NS) served as control data.

RESULTS

Arteriolar density was diminished by 38% (p = 0.004) and %lumen by 13% (p = 0.009) in patients with HCM compared with control subjects. Coronary reserve was impaired in patients with HCM (2.28+/-0.6 vs. 5.34+/-1.49, p = 0.003) because of higher coronary resistance after vasodilation (0.48+/-0.14 vs. 0.22+/-0.06 mm Hg x min x 100 g/ml, p = 0.004). Coronary vasodilator reserve correlated with arteriolar density (r = +0.47, p = 0.045) and with %lumen (r = 0.65, p = 0.003).

CONCLUSIONS

In HCM, the architecture of preterminal subendocardial arterioles is altered by a reduced total cross-sectional lumen area, corresponding to an impaired coronary vasodilator capacity that may predispose to myocardial ischemia.

Changes in phasic coronary blood flow velocity profile and relative coronary flow reserve in patients with hypertrophic obstructive cardiomyopathy

BACKGROUND

In this study, we both investigated coronary flow velocity in hypertrophic obstructive cardiomyopathy (HOCM) and tested the hypothesis of differing coronary flow reserve (CFR) of coronary arteries perfusing left ventricular regions with nonuniform myocardial hypertrophy by measuring the relative CFR.

METHODS AND RESULTS

Coronary flow velocity was assessed in left anterior descending coronary (LAD) and left circumflex (LCX) arteries in 18 patients with HOCM and marked hypertrophy only in the ventricular septum, in 13 patients without obstruction (HCM), and in 9 age- and sex-matched normal subjects at rest, during rapid atrial pacing, and after dobutamine infusion (5 to 30 microg/kg per minute). Relative CFR was estimated as the ratio between absolute CFR of the LAD and absolute CFR of the LCX (LAD/LCX(CF)). At the peak of rapid atrial pacing and during dobutamine stress, LAD/LCX(CF) was reversed in HOCM patients (from 1.25+/-0.11 to 0.82+/-0.07 and 0.79+/-0.06, respectively), whereas it remained unchanged in control subjects (from 1.0+/-0.1 to 1.0+/-0.05 and 1.0+/-0.05, respectively; P<.001). In HCM patients, LAD/LCX(CF) at rest was 1.10+/-0.11, whereas during rapid atrial pacing and dobutamine stress, it was 0.92+/-0.08 and 0.90+/-0.09, respectively. Relative CFR was 0.62+/-0.05 in HOCM patients and 1.05+/-0.05 (P<.001) in normal subjects. There was an inverse correlation between relative CFR and peak systolic outflow tract gradient (r2=.74, P<.001).

CONCLUSIONS

Regional distribution of hypertrophy in some patients with HOCM resulted in regional impairment of coronary flow. Relative CFR can be used to estimate regional disturbances of coronary flow and may help in patient selection for new interventional therapeutic techniques.

Transthoracic Doppler echocardiographic analysis of phasic coronary blood flow velocity in hypertrophic cardiomyopathy

OBJECTIVE

To use transthoracic Doppler echocardiography to assess coronary blood flow non-invasively in patients with hypertrophic cardiomyopathy.

DESIGN

High frequency transthoracic Doppler echocardiography was used to assess resting phasic coronary velocity patterns in patients with hypertrophic cardiomyopathy and to define the relation between coronary flow patterns and clinical, echocardiographic, and haemodynamic manifestations of this condition.

SETTING

A tertiary referral cardiothoracic centre.

METHODS

Fifteen patients (10 men and five women, mean (SD) age 49 (10.3) years) with asymmetric hypertrophic cardiomyopathy underwent high frequency (5 MHz) transthoracic Doppler echocardiographic assessment of the left anterior descending coronary artery. In addition, standard two dimensional echocardiography was performed. The results were compared with 16 normal participants (nine men and seven women, mean age 61.2 (10.7) years) who had no evidence of cardiac disease.

RESULTS

Biphasic diastolic predominant coronary artery blood velocity profiles were obtained in all patients and controls. Systolic peak blood velocity and velocity time integral were significantly reduced in the hypertrophic cardiomyopathy group compared with controls (11.3 (15.8) cm/s and 1.09 (1.78) cm v 20.5 (13.1) cm/s and 4.23 (2.80) cm, respectively, P < 0.05). A reversed pattern of systolic blood flow velocity was found in three patients with severe anterior wall and septal hypertrophy. During diastole there was prolongation of the diastolic acceleration (203 (53) ms v 110 (60) ms in controls, P < 0.05) and deceleration times (487 (200) ms v 210 (90) ms in controls, P < 0.05). There was no significant difference between those with and without symptoms or a left ventricular outflow tract gradient.

CONCLUSIONS

Patients with hypertrophic cardiomyopathy have abnormal systolic and diastolic coronary flow profiles at rest when measured by transthoracic echocardiography.

New diagnostic options in hypertrophic cardiomyopathy

The pathophysiologic features and clinical manifestations of HCM have been elucidated by the introduction of several new diagnostic options. Knowledge of the molecular defects of HCM has advanced rapidly, and genetic screening studies have reemphasized the value of the standard electrocardiogram as an initial screening tool. Analysis of heart rate variability, late potentials, and QT dispersion were not found to be reliable prognostic markers in HCM. However, measurement of dispersion of conduction is probably a sensitive technique in identifying a high risk for sudden cardiac death. Significant developments include transthoracic and transesophageal echocardiography and their role in studying the mitral valve, early detection of left ventricular chamber dilatation, analysis of coronary flow, and intraoperative echocardiography. Finally, advances in the application of magnetic resonance imaging and positron-emission tomography are underway.

Effects of permanent dual chamber pacing on myocardial perfusion in symptomatic hypertrophic cardiomyopathy

OBJECTIVE

Angina and the presence of myocardial ischaemia are common in hypertrophic cardiomyopathy. Dual chamber pacing results in clinical improvement in these patients. This study evaluates the effects of permanent dual chamber pacing on absolute regional myocardial perfusion and perfusion reserve.

SETTING

University hospital.

PATIENTS AND DESIGN

Six patients with hypertrophic cardiomyopathy and severe symptoms of angina received a dual chamber pacemaker. Absolute myocardial regional perfusion and perfusion reserve (dipyridamole 0.56 mg/kg) were measured by dynamic positron emission tomography with 13N-ammonia both during sinus rhythm and 3 months after pacemaker insertion. Results were compared with those from 28 healthy volunteers.

RESULTS

Pacing resulted in a reduction of anginal complaints and a reduction in intraventricular pressure gradient from 65 (SD 30) mm Hg to 19 (10) mm Hg. During sinus rhythm, baseline perfusion was higher in patients with hypertrophic cardiomyopathy than controls (184 (31) v 106 (26) ml/min/100 g, P < 0.01), and perfusion reserve was lower (1.6 (0.4) v 2.8 (1.0), P < 0.05). During pacing myocardial perfusion decreased to 130 (27) ml/min/100 g (P < 0.05), with variable responses in terms of perfusion reserve. Pacing caused a redistribution of myocardial stress perfusion and perfusion reserve. The coefficient of regional variation of myocardial stress perfusion decreased from 19.7 (7.0)% to 14.6 (3.9)% during pacing (12.9 (3.8)% in controls, P < 0.01). The coefficient of regional variation of perfusion reserve decreased from 16.7 (6.6)% to 11.4 (2.6)% during pacing (9.8 (4.1)% in controls, P < 0.01).

CONCLUSIONS

Pacing caused a decrease of resting left ventricular myocardial blood flow and blood flow during pharmacologically induced coronary vasodilatation. Although global perfusion reserve remained unchanged, myocardial perfusion reserve became more homogeneously distributed.

Velocity-encoded, phase-difference cine MRI measurements of coronary artery flow: dependence of flow accuracy on the number of cine frames

Phase-contrast magnetic resonance imaging (PC-MRI) can be used to produce multiframe cine flow images of the coronary arteries. Accurate coronary flow measurement requires the elimination of respiratory motion artifacts using k-space segmentation to acquire the data in a single breath-hold. However, the duration of the breath-hold is proportional to the number of cine frames. In the present study, the number of cine frames was varied and the accuracies of the coronary flow measurements were assessed using perivascular US. For the range of flows studied (2 ml/min to 147 ml/min), the correlation coefficients for PC-MRI and US increased (.70-.98) and the limits of agreement improved (+/-45 ml.min-1 to +/-10 ml.min-1) as the number of cine frames increased from one to six. The results suggest that the accuracy of breath-hold cine PC-MRI measurements of coronary artery flow improves as the number of cine frames increases.

Coronary flow reserve and exercise capacity in hypertrophic cardiomyopathy

The aim of this study was to evaluate the relation of coronary flow velocity (CFV) and coronary flow reserve (CFR) to exercise capacity in ten verapamil-treated patients with hypertrophic cardiomyopathy (HC). Using Doppler transesophageal echocardiography, we assessed diastolic CFV in the proximal left anterior descending coronary artery at baseline and after administering 0.56 mg/kg intravenous dipyridamole. The CFR was calculated as the post-dipyridamole/baseline diastolic CFV ratio. A maximal symptom-limited exercise treadmill test was performed according to a modified Bruce protocol and the exercise capacity was expressed as metabolic equivalents. The mean value for baseline diastolic CFV was 59 +/- 27 cm/s; this increased after dipyridamole to 134 +/- 57 cm/s. The CFR was 2.37 +/- 0.67. Baseline diastolic CFV correlated negatively with both exercise duration (r = -0.69; P < 0.05) and value for metabolic equivalents (r = -0.70; P < 0.05). CFR was weakly and non-significantly related to exercise duration (r = 0.40; P > 0.05) and to the value for metabolic equivalents (r = 0.32; P > 0.05). Shortening of exercise time and decreasing metabolic equivalents were correlated with increased baseline diastolic CFV. Dipyridamole-assessed CFR, was weakly related to parameters of exercise capacity.