Usefulness of coronary flow reserve measured by transthoracic coronary Doppler ultrasound in the elderly

Noninvasive measurement of coronary flow reserve (CFR), defined as the ratio of maximal to baseline coronary blood flow, has been repeatedly shown to be a feasible technique by ultrasound transthoracic Doppler (TTD) both in the LAD and, with some limitations, in the posterior descending (PD) coronary artery. CFR by TTD offers two important pieces of information: information about patency and flow through the large epicardial coronary artery proximal to the site of CFR assessment and information distal to the site of CFR assessment. CFR by TTD is a valuable research tool for investigating the pathophysiology of coronary circulation. However, CFR by TTD is also an important clinical decision-making instrument, enabling functional assessment of epicardial coronary stenosis, particularly in cases of anatomically borderline stenosis, i.e., 50%–70% of cases. CFR by TTD enables insight downstream into coronary microvascular function that might be impaired due to primary coronary microvascular disease, as a consequence of myocardial diseases with extramural compression and microvascular remodeling and rarefaction (in left ventricular hypertrophy, dilated or hypertrophic cardiomyopathy, or aortic stenosis), or as a consequence of microvascular obstruction due to micro-embolization by plaque and thrombus debris during percutaneous coronary interventions. As a technique that is noninvasive, inexpensive, easily repeatable, and that does not require radiation, TTD CFR may be very useful in the fragile population of the elderly, offering a better understanding of coronary vascular aging as well as clinically important information regarding the diagnosis and prognosis of coronary artery disease.