Despite significant improvements for earlier detection of and medical therapies for heart failure, a recent American Heart Association (AHA) study stated that the actual incidence of heart failure has not declined. Of interest is the fact that the AHA found hypertension precedes development of heart failure in 91% of cases. The increasing prevalence of these combined disease states escalates the cost of national healthcare. Further, many patients not compliant with medical therapies and lifestyle changes elevate their risk of continuing progression of their heart failure, eventually requiring device implantation. These devices capable of defibrillation (implantable cardioverter defibrillators, ICDs) and cardiac resynchronization therapy (CRT) offer proven benefits in length and quality of life for many, but also increase the financial burden of providing such medical care.
The presence of such therapeutic techniques that improve survivability without consecutive decline in prevalence offers the medical community a significant challenge: to detect and treat heart failure at its earliest stages in the hope of reversing the upward curve in this burgeoning patient population.
Dramatic improvements in applications and clinical experience regarding the use of transthoracic 3-D cardiac ultrasound is well documented. Recently, the American Society of Echocardiography (ASE) endorsed the use of 3-D transthoracic echocardiography (TTE) in clinical practice for accurate evaluation of cardiac mass, left ventricular (LV) volumetric function analysis, and assessment of valvular disease. Each of these applications provides critical physiological data that may be followed serially in the progression or regression of heart failure.
One of the known hallmarks in chronic hypertension is the increase of gross LV cardiac mass, coupled with diastolic dysfunction. In fact, past studies have demonstrated increased morbidity and mortality in this population. Where common 2-D echocardiography measures (M-mode) yield gross estimations of LV mass, 3-D echocardiography provides rapid objective measurements derived from the identical wide-angle acquisition from which volumetric data are obtained. Along this continuum, actual scanning time will become progressively shortened as 3-D echocardiography applications and processing speed improve.
The importance of immediate and safe availability in obtaining such serial clinical measurements may best be highlighted in a progressive algorithm of the average referral patient from the primary care physician for cardiology consultation. This patient might be a middle-aged male of 49 years with hypertension (160/95), who is moderately obese, and who has relatively poor lifestyle habits. There may be a history of tobacco use, as well as glucose intolerance or type 2 diabetes. Clinically, this patient may present with symptoms of LV diastolic and/or systolic dysfunction and complain of poor exercise tolerance and shortness of breath with generalized fatigue. Presence of sleep apnea may also be suspect as a contributor to progressive heart failure and edema.
During evaluation, the initial 2-D echocardiography examination will provide important values of chamber dimension, diastolic function, and Doppler assessment for cardiac hemodynamics. From this point, however, the adjunctive 3-D echocardiography offers specific incremental value in measuring objective changes in LV end diastolic and systolic volumes, from which a full 17-segmental ejection fraction may be derived. These rapid 4–7-second, wide-angle acquisitions have recently improved capabilities to obtain higher frame-rate (25–42fps) images without pharmacological enhancement, yet offer improved temporal resolution and specificity of regional wall motion.
Using these improved techniques, the goal is to correlate adequate medical control of hypertension in the hope of seeing a subsequent reduction in LV mass and LV end diastolic volume and preserved EF >55%. If the patient remains poorly controlled or non-compliant to therapies, we may conversely see increased LV mass (see Figure 1), coupled with an increase in pre-load (LV end diastolic volume, LVEDV) and decreased ejection fraction. In the busy clinical practice, the ability for sonographers to quickly acquire and calculate such data from a single wide-angle acquisition is productive, and ensures excellent comparison from one parameter to another and from one serial exam to another in reproducible fashion.
With further progression, clinically we reach a point where many consults present with suspicion for the presence of coronary artery disease (CAD) or ischemic cardiomyopathy. Hallmarks for CAD include both diastolic and systolic dysfunction. These are often treated with combined therapies, including beta-blockade, afterload reduction, and diuretics. Acute volume changes with such treatments can accurately be compared with baseline or pre-therapeutic states, and should provide more intuitive and objective guidelines in the future. It is important to note that absolute objective and reproducible LV volumes and ejection fraction can play a large role in the advancement of prevention and treatment of heart failure. Visual estimation is, in truth, inadequate, and the bias of such introduces subjectivity in measuring outcomes. With a broad platform of reliable, serially derived data, we can move confidently towards improved guidelines for medical therapies.
Many heart failure-related volume overload states are associated with malfunction of the mitral valve apparatus and aortic stenosis or regurgitation. Whether due to altered geometry or restriction of the leaflets, or ischemic in nature (see Figure 2), the resultant volume displacement into the left atrium from mitral regurgitation may produce a further increase in cardiac chamber volumes and pressures.
In the clinical setting, this patient would have adjunctive 3-D volumetric and anatomical imaging protocols performed to assess the relationship between ventricular and valvular disease states. Live, 3-D, high-frame-rate imaging provides high-resolution images of valvular structures that can be cropped and manipulated in realtime 3-D fashion (see Figure 2). In this way, the interpretative cardiologist or surgeon views the encapsulated mitral valve in realtime and real space, surveying the primary anatomical abnormalities that cause regurgitation.
A trend in the standard of care today is geared toward earlier detection and repair of the mitral valve, with a close eye on the longevity of that repair. We know that LV geometry post-repair is an important component of that longevity. Using 3-D echocardiography to interrogate valvular anatomy and physiology will allow for more intelligent discussion of the morphological abnormalities, which in turn will assist surgeons to restore the geometry and physiology of valvular function and consequently durability of repair. With earlier repair and more aggressive guidelines regarding the progression of left atrial dilatation, there is a hope of decreased prevalence of subsequent atrial arrhythmias—i.e. atrial fibrillation—which present the undesirable cascade of diastolic dysfunction and increased risk of long-term anticoagulation therapies as well as outcomes.
As the population of implant subjects who benefit from CRT increases, it is important to have less expensive and more productive tools that are widely available to assess and track progress from both a clinical and a therapeutic standpoint. Perhaps it is in this rapidly paced arena where 3-D echocardiography may play its biggest role of all.
The recent addition of parametric time to peak and wall motion mapping helps to differentiate regional volume displacement in both idiopathic and ischemic hearts. Adding this data to current standards of color tissue Doppler strain imaging for time to peak velocity, we have a broad spectrum of data concerning not only who the responders to CRT are, but also why they respond. In the current state, we know that 30% of the implanted patients with a wide QRS do not respond to CRT. In the search for the 30% who will respond, we believe 3-D echocardiography will help to bridge the chasm between these two realities of the group that is likely being denied treatment by current implantation standards. The development of the Systolic Dyssynchrony Index, as described by Monaghan at King’s Daughters in London, has demonstrated a strong correlation to responders versus non-responders independent of cardiomyopathy origins. We would like to see this work continue in larger, multicenter, randomized trials in the future.
Beyond pre-assessment for responders to CRT implantation, early use of 3-D echocardiography for V-V optimization of these resynchronization devices has begun.
Being able to accurately measure global and regional volume changes in vivo during actual optimization may have a broad impact on understanding specific elements in how various V-V timings benefit gross stroke volume and cardiac output in all cardiomyopathy types. A recent case study as part of a single-site trial at Saint Thomas Heart Institute revealed supportive data: the maximal end diastolic volume coupled with the optimal forward stroke volume also correlated well with expected decrease in Systolic Dyssynchrony Index and improved synchronous volume displacement by 3-D echocardiography.
Further research may indeed move us towards the common denominator of stroke volume and cardiac output as a guideline for device optimization. By this, perhaps other established abnormalities associated with LV mechanical dyssynchrony may be more simply expressed as derivatives of inadequate diastolic-filling and volume-loading conditions. Time and research will demonstrate these facts in terms of outcomes over the next few years.
Further use of 3-D echocardiography techniques are likely to produce additional software applications that will assist in trials for internal automation of intelligent device therapies in the future in regard to maximal stroke volume in variable control states.
In this new and enlightened era of computer-assisted medical imaging, we address a paradigm shift in what diagnostic data it is important to obtain and track because it is now more accessible to broad populations in the clinical setting. For our model heart failure patient, we have simple-to-use, immediate bedside tools that quickly produce a wealth of information on these patients, using the new 3-D language of volumes rather than dimensions. Learning to speak this language of realtime intra-cardiac volume changes will enhance the understanding of relational hemodynamics and the growth of volumetric echocardiography.
Directives for digitalization and collection for national databases will have exponential effects on our understanding of outcomes pertaining to all therapies. As the role of 3-D echocardiography is continually refined and redefined, 64-bit microprocessing capabilities will enter the stage, causing a dramatic leap in high-speed, large-file images that can be instantaneously integrated with cross-modalities.
As for the new-found clinical prognostic value for 3-D echocardiography, we as clinical cardiologists must be prepared to embrace the changes, set the bar higher, and resolve ourselves to be not spectators of the future, but architects of it. It is only real-world use and improvements in our patients that ensure the survival and growth of such important shifts in diagnostic imaging.