Update on cardiac imaging techniques 2013

Cardiac imaging is a cornerstone of diagnosis in heart conditions, and an essential tool for assessing prognosis and establishing treatment decisions. This year, echocardiography stands out as a guide in interventional procedures and in choosing the size of the prosthesis. It is also proving to be a valuable technique in low-flow, low-gradient aortic stenosis. Three-dimensional echocardiography is advancing our knowledge of cardiac anatomy and valvular measurements. The parameters indicating tissue deformation have predictive power in valve disease and in the follow-up of drug-induced cardiotoxicity. Single-photon emission computed tomography and positron emission tomography are proving useful in ischemic heart disease and in the diagnosis of cardiac inflammation and infections. The role of computed tomography has been strengthened in noninvasive coronary angiography, the emergency room management of chest pain, assessment of chronic occlusions, and morphologic study of coronary plaque. Cardiac magnetic resonance imaging remains the gold standard for tissue characterization in ischemic heart disease and cardiomyopathies, and is assuming a greater role in stress studies and in the assessment of myocardial viability.

Left atrial function by two-dimensional speckle-tracking echocardiography in patients with severe organic mitral regurgitation: association with guidelines-based surgical indication and postoperative (long-term) survival

BACKGROUND

Left atrial (LA) mechanics in patients with severe mitral regurgitation (MR) remain largely unexplored. The aim of the present evaluation was to assess the effect of severe MR on LA function, its potential relation with conventional surgical indications, and long-term postoperative survival.

METHODS

Two-dimensional speckle-tracking strain and volumetric indices of LA reservoir, conduit, and contractile function were assessed in 121 patients with severe MR and 70 controls. Patients were divided according to the presence (n = 46) or absence (n = 75) of one or more guidelines-based criteria for mitral surgery (symptoms, left ventricular ejection fraction ≤ 60%, left ventricular end-systolic diameter ≥ 40 mm, atrial fibrillation, or systolic pulmonary arterial pressure >50 mm Hg).

RESULTS

In patients with severe MR compared with controls, significant LA reservoir and contractile dysfunction was observed, which was more pronounced in patients with mitral surgery indication (P < .05 for all strain and volumetric indices). Of all indices of LA function, LA reservoir strain was an independent predictor (odds ratio, 0.88; 95% confidence interval, 0.82-0.94; P < .001) and had the highest accuracy to identify patients with indications for mitral surgery (area under the receiver operating characteristic curve, 0.8; 95% confidence interval, 0.72-0.87). A total of 117 patients underwent mitral valve surgery. Patients with LA reservoir strain ≤24% showed worse survival at a median of 6.4 years (interquartile range, 4.7-8.7 years) after mitral surgery (P = .02), regardless the symptomatic status before surgery. LA reservoir strain, on top of mitral surgery indications, provided incremental predictive value for postoperative survival.

CONCLUSIONS

Impaired LA reservoir strain in patients with severe organic MR relates to long-term survival after mitral valve surgery, independently of and incremental to current guidelines-based indications for mitral surgery.

Effect of electrical stimulus parameters on the development and propagation of action potentials in short excitable fibres

Intracellular action potentials (IAPs) produced by short fibres in response to their electrical stimulation were analysed. IAPs were calculated on the basis of the Hodgkin-Huxley (1952) model by the method described by Joyner et al. (1978). Principal differences were found in processes of activation of short (semilength L less than 5 lambda) and long fibres under near-threshold stimulation. The shorter the fibre, the lower was the threshold value (Ithr). Dependence of the latency on the stimulus strength (Ist) was substantially non-linear and was affected by the fibre length. Both fibre length and stimulus strength influenced the IAP amplitude, the instantaneous propagation velocity (IPV) and the site of the first origin of the IAP (and, consequently, excitability of the short fibre membrane). With L less than or equal to 2 lambda and Ithr less than or equal to Ist less than or equal to 1.1Ithr, IPV could reach either very high values (so that all the fibre membrane fired practically simultaneously) or even negative values. The latter corresponded to the first origin of the propagated IAP, not at the site of stimulation but at the fibre termination or at a midpoint. The characters of all the above dependencies were unchanged irrespective of the manner of approaching threshold (variation of stimulus duration or its strength). Reasons for differences in processes of activation of short and long fibres are discussed in terms of electrical load and latency. Applications of the results to explain an increased jitter, velocity recovery function and velocity-diameter relationship are also discussed.