Heart 1997;78:213-214 213 Editorial Heart: first published as 10.1136/hrt.78.3.213 on 1 September 1997. Downloaded from Aortic stenosis and angina with normal coronary arteries: the role of coronary flow abnormalities Angina is a common symptom among patients with signif- hypothesis: that the epicardial coronary vasculature, while icant aortic valve stenosis. The incidence of between 60% initially adapting to produce higher rates of blood flow and 80% is notably higher than that observed in other to the hypertrophied myocardium in aortic stenosis, valve diseases.12 In addition, a considerable proportion of ultimately fails to keep pace as the degree of hypertrophy patients with angina and aortic stenosis are found to have worsens. This concept is further supported by the findings normal coronary arteries at angiography despite having that during vasodilator stress maximal indexed coronary objective evidence of myocardial ischaemia on electro- flow and the maximal/resting flow ratio (that is, coronary cardiographic or radionuclide evaluation'3 4 and, more flow reserve) are significantly reduced and indexed coro- recently, stress echocardiography.5 Why should aortic nary artery resistance increased in aortic stenosis.8 10 The stenosis provoke angina in patients without significant hypertrophied ventricle is thus rendered susceptible to obstructive coronary artery disease? The presence of left ischaemia under conditions of increased workload, even in ventricular hypertrophy undoubtedly plays a role, but the absence of significant coronary artery stenoses. recent Doppler echocardiographic studies of the coronary vasculature in aortic stenosis have demonstrated abnormal phasic flow profiles that may shed light on the mechanism Phasic coronary flow in aortic stenosis of ischaemia in this condition. Coronary flow reserve calculations are typically derived from flow catheters positioned in the coronary sinus. This technique, however, provides little meaningful informa- Role ofleft ventricular hypertrophy tion regarding phasic flow across the left ventricular vascu- The development of left ventricular hypertrophy has been lature during systole and diastole. With recent advances in shown to produce considerable impairment of coronary Doppler ultrasound technology permitting measurement flow reserve in a variety of conditions associated with of flow velocities within epicardial coronary arteries, this chronic pressure overload, including aortic valve disease.6 aspect of coronary flow and its possible relation to the Reduced flow reserve is known to provoke ischaemia in generation of ischaemia has received renewed interest. these conditions and has been cited as the possible cause In the normal situation, blood flow through the left http://heart.bmj.com/ of angina in aortic stenosis.7 However, it is well known coronary arterial system is biphasic, with the majority of that replacement of the aortic valve relieves angina in the flow occurring in diastole. The contribution of systolic immediate postoperative period before any significant flow is, however, not insignificant. An eloquent series of change in the degree of hypertrophy, indicating that canine studies by Gregg in the 1960s'1 using volumetric impaired flow reserve is not the whole story. Myocardial flow catheters demonstrated systolic flow to be of the wall tension (and thus myocardial oxygen demand) order of 20-30% of total left coronary flow at rest. is increased and coronary perfusion pressures decreased in Moreover, it was noted that as total left coronary flow aortic stenosis; both will be ameliorated immediately fol- increased during exercise, the ratio of the systolic to dias- on September 30, 2021 by guest. Protected copyright. lowing valve replacement when the obstruction to left ven- tolic components remained the same or even increased. It tricular outflow is relieved. Thus an imbalance between was also shown that much of the measured systolic flow oxygen supply and demand also seems likely to be impli- represented true intramural flow rather than epicardial cated in the genesis of ischaemia in this condition. flow. It is therefore possible that abnormalities of systolic as well as diastolic coronary flow may have deleterious CORONARY FLOW RESERVE IN AORTIC STENOSIS effects on the metabolic supply and demand of the Resting epicardial coronary artery blood flow has been myocardium. shown to be increased in patients with aortic stenosis.8 In Although Doppler techniques provide velocity rather addition, Villari et a?g have shown that the left (but not the than volumetric flow data, important information regarding right) coronary artery cross-sectional area is significantly the systolic and diastolic components of coronary flow can greater in patients with aortic stenosis and left ventricular still be obtained. Flow velocity profiles in the left anterior hypertrophy compared with controls without hypertrophy. descending artery in patents with aortic stenosis and These findings are likely to reflect an attempt by the coro- normal coronary arteries have been examined in several nary vasculature to keep up with the increasing metabolic studies using intravascular ultrasound,'2 13 and both trans- demand of the hypertrophied left ventricle. Indeed, when oesophageal14 15 and transthoracic echocardiography.'6 coronary flow is indexed to unit left ventricular mass in Certain abnormal velocity profiles have been identified this situation, resting indexed flow is in fact normal.8 that provide new insights into the mechanism of ischaemia Similarly at the outset of Villari's study when left coronary in this group. artery area was indexed per 100 g of left ventricular muscle mass, there was no difference between indexed left coro- SYSTOLIC FLOW nary artery area in patients with aortic stenosis and con- In aortic stenosis, peak systolic flow velocities in the left trols. However, as the degree of hypertrophy increased coronary artery tend to be reduced, with a significant during the course of that study, the indexed left coronary number of patients displaying reversal of flow in sys- artery area became significantly reduced in the aortic tole.12-16 The extent of these changes shows good correla- stenotic group. These findings present an interesting tion with the pressure gradient across the aortic valve'2 214 Editorial and the systolic left ventricular wall stress index.'5 Similar valve replacement. Surgery is therefore a necessity in this changes are not seen in the right coronary artery"2 nor situation irrespective of other findings. However, if it can be indeed in patients with left ventricular hypertrophy with- shown that the degree of coronary flow abnormality is cor- out aortic valve obstruction.14 These changes may there- related with prognosis it may be possible to use this infor- fore relate to the marked discrepancy between left mation to prioritise symptomatic patients awaiting valve Heart: first published as 10.1136/hrt.78.3.213 on 1 September 1997. Downloaded from ventricular intramyocardial pressures and coronary perfu- replacement. What are the implications for patients without sion pressure during systole in subjects with significant symptoms? Their prognosis appears to be significantly aortic stenosis. better (even in the presence of severe stenosis) and it has been argued that completely asymptomatic patients with DIASTOLIC FLOW aortic stenosis should not be operated on until symptoms Diastolic flow velocity profiles in aortic stenosis appear to develop.'7 It is interesting that coronary flow profiles in be more heterogeneous and are therefore difficult to inter- asymptomatic patients with aortic stenosis appear to be pret. These tend to display rather slower acceleration and similar to normal, which would be consistent with the more rapid deceleration to and from peak velocity of flow more benign outlook. It is not yet clear whether flow profile than in normal subjects.12 15 In addition, while peak dias- changes occur before the development of symptoms. If tolic velocities do not seem to change in the same way as this is the case it may be possible to use the change in flow systolic velocities in relation to transvalvar gradient, there is profile as an indicator for valve replacement rather than some evidence that they are increased in patients who waiting for overt symptoms to appear. complain of angina symptoms.'4 15 The mechanism of These concepts are of course speculative and much these diastolic changes is speculative, but may relate to a work needs to be done. However, it seems likely that as high end diastolic pressure (and thus wall tension) our understanding of this complex situation increases, decreasing acceleration of flow in diastole by a combina- coronary flow profile data will establish a useful clinical tion of increased coronary impedance and decreased rela- role in the management of patients with aortic stenosis. tive coronary perfusion pressure. TIMOTHY IRVINE ANTOINETTE KENNY The combination of reduced or absent systolic flow plus Regional Cardiothoracic Centre, increased impedance of diastolic flow to the left ventricle Freeman Hospital, may, on the background of impaired coronary flow Newcastle upon Tyne NE7 7DN, United Kingdom the link" in the of reserve, provide "missing pathogenesis 1 Morrison GW, Thomas RD, Grimmer SFM, Silverton PN, Smith DR. angina in aortic stenosis. Furthermore, it has been shown Incidence of coronary artery disease in patients with valvular heart dis- that both the abnormal and diastolic ease. BrHeartj 1980;44:630-7.