New Diagnostic Modalities in the Diagnosis of Heart Failure: part 2

16 Jan
2010

Valuable cardiac information can be obtained from the echocardiogram. The size, shape, and function of the ventricles along with regional wall motion can be attained. The presence of thrombus can often be identified depending on its size and location in these patients who have a high risk for the development of thrombotic events. Identification of valvular abnormality, especially mitral regurgitation (MR), aortic stenosis (AS), and aortic regurgitation (AR) is important and can impact treatment options, preventing HF for those at high risk. Mitral valvuloplasty in severe MR and aortic replacement in significant AS or AR may improve left ventricular function and HF symptoms if correct timing of surgery is achieved. Other information that can be obtained from a routine echocardiogram include estimate of pulmonary pressures, presence and severity of diastolic dysfunction, and left ventricular hypertrophy. Presence of significant pericardial efftision can also be assessed.

However, obtaining an echocardiogram and having it interpreted in a timely manner is not always feasible. Echocardiography may have limited availability, depending on the time of day the study is needed. In addition, patients with comorbid conditions, such as chronic obstructive pulmonary disease and obesity, usually have poor acoustic windows rendering the test technically difficult if not impossible to perform. Tests like an electrocardiogram (ECG) are important but have no specific diagnostic features. A chest x-ray is frequently employed to evaluate the presence of congestion and cardiomeagly. However, it has many limitations, including low sensitivity and delayed correlation with clinical status changes.
Despite a good patient history, physical examination, and available diagnostic tests, with known limitations, the percentage of initial correct diagnosis of HF remains low. There is a search for additional tests to assist with initial HF diagnostic accuracy. Once the correct diagnosis is made, the question of early identification of acute symptoms indicative of decompensation needs to be addressed. Recognizing acute decompensations is often problematic because there are other diseases, such as depression and sepsis, that can mimic the symptoms. The capability of predicting decompensations enhances the diagnostic and therapeutic possibilities in this population. Healthcare professionals can predict the increased hospitalizations characteristically observed in HF patients after major holidays, such as Thanksgiving, July 4th, and Christmas. This is typically secondary to dietary indiscretions, the basis for a significant percentage of acute HF decompensations leading to hospitalizations.

There are two new diagnostic modalities that offer promise in improving HF diagnostic accuracy and possibly predicting or identifying early acute HF decompensations. These are impedance cardiography (ICG) (BioZ®, ICG Monitor, CardioDynamics International Corporation, San Diego, CA) and the B-type natriuretic peptide assay (BNP). silagra

Figure 2

Figure 2.

Impedance cardiography is a test as simple to perform as an ECG that provides clinically useful, noninvasive hemodynamic information. ICG requires four sets of dual sensors, two sets attached at the base of the neck and two sets attached at the side of the patient’s chest at the level of the xiphoid process in the mid-axillary line (Figure 2). The skin is prepared similar to the pre-ECG skin preparation. The inner sensors measure the baseline impedance to a low amplitude alternating current transmitted via the outer sensors. With each heartbeat, ICG measures the corresponding change in impedance. The baseline and the subsequent changes in impedance are used to calculate hemodynamic parameters. These parameters include cardiac output/cardiac index; stroke volume/stroke index; systemic vascular resistance/systemic vascular resistance index; measures of contractility, such as systolic time ratio, velocity index, and accelerated cardiac index; and thoracic fluid content (TFC). The TFC represents the total fluid content of the thorax (intravascular, intra-alveolar and interstitial). Therefore, a high TFC value indicates an excess of total thoracic fluids. ICG is a validated, noninvasive method of determining hemodynamic parameters. Studies have documented its accuracy in comparison with Fick and thermodilution methods in critically ill patient populations. cheap cialis canadian pharmacy

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