Not only is heart failure one of the single biggest causes of morbidity and mortality in man, but the incidence of the condition is steadily increasing. Rising to this challenge, innovative medical diagnostic techniques with ever greater performance are constantly being introduced so that early, unambiguous detection of the underlying condition is now possible, enabling the prompt initiation of targetted therapies. This article presents a brief review of the most relevant diagnostic techniques, their current status and their indications.
By O. Ekinci, M.D.
Some 14 million people in Europe currently suffer from heart failure with the number predicted to increase to no fewer than 30 million by 2020. The medical impact of heart failure is huge — in particular, the condition is associated with high mortality. After the first incident of cardiac decompensation, as many as around 40 percent of patients will die within one year. Of those who survive the first year only one third will actually live longer than a further 5 years. In addition to such alarming medical statistics, the social impact of heart failure is also significant and is understandably associated with immense costs, which put an additional financial strain on already tight healthcare budgets.
For all these reasons, the early detection and adequate treatment of cardiac diseases is of the greatest importance, since this is the only way to prevent subsequent damage to the myocardium and to avoid permanent limitations on the quality of life of the patient.
The latest developments in imaging and in vitro diagnostics offer new opportunities for detecting heart failure not only much earlier but also with great precision.
Echocardiography: from 2D to 4D
Ultrasound examination of the heart, i.e. echocardiography, is the basic imaging technology (and also the least expensive one) in cardiology, and, in the vast majority of patients, plays the role of a “Gatekeeper” controlling access to eventual additional diagnostic procedures that may be needed. The latest echocardiography systems now enable real-time three-dimensional images of the beating heart so that the heart can be imaged as a whole organ easily and rapidly, and not just in 2D images, but in full volumes. The latest echocardiography systems can display and analyze the heart in full after a single heartbeat. Such echocardiography results are the prerequisite for other, more expensive examinations, which may be necessary. Echocardiography is widely available in hospitals and in nearly all cardiology practices, while newer imaging technologies such as cardiac CT or MRI, which may be indicated for further diagnostic investigation are in general found mostly
in larger facilities.
The heart in the magnet:
cardiac MRI
One of the most recent imaging techniques being used to analyze the heart is magnetic resonance imaging (MRI), which, in addition to the fact that it does not involve the use of ionizing radiation, in contrast to CT, provides a comprehensive (and highly accurate) assessment of the heart. Cardiac magnetic resonance imaging (CMR) can also yield penetrating insights into the underlying pathology of a failing heart. Known as the gold standard for the assessment of cardiac function, cardiac MRI is used as the most accurate non-invasive tool to measure parameters like ejection fraction, based on which patients may get a drug therapy alone or even devices implanted (such as pacemakers or defibrillators). CMR also provides a special imaging approach for the visualization of even the smallest scars in the myocardium [Figure 1], which is important since the presence and extent of myocardial scarring is a major risk factor for sudden cardiac death
[Ref. 1]. It has been shown in many recent clinical studies, that CMR allows accurate assessment of myocardial scar formation with extremely high diagnostic accuracy. CMR is the best non-invasive approach to address this important clinical question [Ref. 2]. For this reason, a growing number of cardiologists are using the procedure to identify patients with severe heart failure who are in need of an implantable defibrillator, which protects against cardiac arrest through targeted shock delivery.
Until recently, because of the high magnetic fields used in the technique, CMR was contraindicated in patients with pacemakers. Thanks to cooperative development between the manufacturers of MRI systems on the one hand and pacemaker devices on the other, MRI-conditional pacemakers* are beginning to become available (e.g. from Medtronic). Since MRI scanners may cause traditional pacemakers to misinterpret MRI-generated electrical noise and withhold pacing therapy or deliver unnecessary pacing therapy, the new generation of pacemakers include features that set the device into an appropriate mode for the MRI environment. Such pacemakers also include hardware modifications to the device and leads that are designed to reduce or eliminate the influence of the MRI environment.
At the practical level, MR examinations of the heart are no longer complicated or time-consuming. In general, a CMR examination for the evaluation of cardiac anatomy, function and scarring can now be carried out within 20 minutes.
Coronary vessels in view: cardiac CT
Computed tomography (CT) has long had a valuable role in early disease detection over the years. Steady technological development over the years means that the latest generation of CT scanners can now carry out coronary CT angiography (CTA) with significantly reduced radiation dose [Figure 2]. The most recent innovation, namely the use of ECG-triggered high-pitch spiral data acquisition using dual source CT as implemented in the Definition Flash system from Siemens can carry out CTAs at radiation doses as low as below 1 mSv, which is less than in conventional coronary angiography. [Ref. 3] (By comparison, one mSv is less than half of the annual natural background radiation on earth, to which everyone is exposed).
Unlike a cardiac catheter examination, CT can not only visualize the coronary lumen, but also display deposits (plaque) in the coronary wall. The calcium load of the coronary vessels (known as the Calcium Score) can be quantified in CT without the use of contrast agent. An age-adapted increased calcium load of the coronary arteries is as much a risk factor as smoking or increased cholesterol. Recent studies have shown that high Calcium Score can modify predicted risk obtained from traditional risk stratification tools (e.g. Framingham Risk Score) alone, especially among patients in the intermediate risk category in whom clinical decision making is most uncertain [Ref. 4]. In practice, using the latest technology coronary CT examinations can be carried out in less than a second and are therefore especially useful in patients with cardiac arrhythmias and older patients since the short time-span means that the patients can breathe normally [Figure 3]. The procedure is also optimal and time-efficient for the physician, since now a single mouse click generates a meaningful image, where previously lengthy image processing was necessary.
Of course, such innovations inevitably have their price. However, it is important to realize that the appropriate use of these new technologies may save overall health care expenditure over the long term: thanks to better diagnostics, treatment can be initiated much sooner. As a consequence, quality of life can be preserved and loss of productivity avoided.
Minimally invasive therapy: intervention instead of surgery
Some underlying diseases of heart failure — such as severe valvular disease — often require therapeutic interventions beyond drug therapy involving cardiologists and surgeons at the same time. The cardiac cath. lab of the future is already being implemented in some centers in the so-called Hybrid-ORs which, by bringing together the features of the surgical room with those of a cath lab, make possible innovative therapies, such as in the treatment of severe aortic valve stenosis. Until now, valve replacement by open-heart surgery was the recommended therapy approach in these cases, but in many elderly patients with concomitant diseases this can be too risky. Interventional implantation of an aortic valve prosthesis has become an alternative in such patients, and can give rise to rapid improvement of cardiac parameters. In this procedure the valve prosthesis is placed via the femoral artery or, if this is not possible, by a small incision in the apex of the heart. Such a ‘minimally invasive’ intervention puts much less stress on the patient, than an open heart operation. Overall, providing technical equipment needed to accommodate multiple specialties in one lab may allow for better quality of care as well as better time and cost efficiency, both for the patient and the institution.
Drop by drop to diagnosis: biomarkers
The presence and course of heart failure can also be assessed using in vitro lab tests, through the use of new biomarkers which, especially in emergency care, can influence and support clinical decisions. In heart failure the use of circulating B-Natriuretic peptide (BNP) is particularly relevant, since the level of this biomarker is a good indicator of the degree to which the cardiac function is impaired. BNP is used both for initial diagnosis and for therapy monitoring. Recent studies have shown that in the presence of other risk factors and known HF, BNP has also a prognostic value, i.e. patients with BNP above a certain level will be candidates for more aggressive risk
management [Ref. 5].
In many patients, a heart attack is the direct cause of cardiac insufficiency, so fast detection of a myocardial infarction (MI) is extremely important in order to prevent severe myocardial damage and subsequent heart failure. To do this, more and more emergency rooms routinely use high sensitive troponin I tests as an early and precise indicator of MI [Ref. 6]. Significant time can be saved in this way so that the recommended therapy, such as the reopening of the occluded coronary artery by cardiac catheterization can be initiated immediately. Since, for every second that the coronary artery remains occluded muscle cells will die (in the classical dictum “time is muscle”) rapid intervention is of course vital.
References
1. Assomull et al. Cardiovascular Magnetic Resonance, Fibrosis, and Prognosis in Dilated Cardiomyopathy. J Am Coll Cardiol 2006; 48: 1977-85.
2. Kim HW et al. Cardiovascular magnetic resonance in patients with myocardial infarction: current and emerging applications. J Am Coll Cardiol 2009 Dec 29;55(1):1-16
3. Achenbach et. al. Coronary computed tomography angiography with a consistent dose below 1 mSv using prospectively electrocardiogram-triggered high-pitch spiral acquisition. Eur Heart J. 2010 Feb;31(3):340-6
4. Polonsky TS et al. Coronary artery calcium score and risk classification for coronary heart disease prediction. JAMA 2010 Apr 28;303(16):1610-6.
5. McKie et al. The Prognostic Value of N-Terminal Pro–B-Type Natriuretic Peptide for Death and Cardiovascular Events in Healthy Normal and Stage A/B Heart Failure Subjects. J Am Coll
Cardiol. 2010;55:2140–7.
6. Bonaca M et al. Prospective Evaluation of the Prognostic Implications of Improved Assay Performance With a Sensitive Assay for Cardiac
Troponin I. J Am Coll Cardiol. 2010;55:2118–24
The author
A cardiologist by training, Okan Ekinci, M.D.,
is a Cardiac Imaging Expert and
Lecturer for Cardiovascular MRI
at the Medical University of Vienna (Austria) and University College Dublin (Ireland).
Contact: okanekinci@yahoo.de
