Left ventricular effects on right ventricular developed pressure.

The possibility that left ventricular (LV) performance might affect right ventricular (RV) function through the myocardium was examined by using isolated, flow-perfused, paced rabbit hearts beating isovolumically. Reducing LV volume from its optimal volume to zero caused a 5.7% decrease (N = 10, P less than 0.001) in right ventricular developed pressure (RVDP). Ligating the anterior ventricular branches of the left coronary artery which in the rabbit supply the LV free wall resulted in an additional 9.3% decrease in RVDP (N = 5, P = 0.05) within 3 min of ligation. Finally, cutting the LV free wall from the atrioventricular orifice to the apex (thereby preventing any developed LV free wall force during systole) caused a 45% further decrease in RVDP (N = 2, P less than 0.02). Cineradiographic study showed that the alterations in RVDP resulting from changes in LV volume and coronary occlusion correlated significantly (N = 5, P less than 0.01) with the magnitude of septal bulging into the RV cavity during systole. The results indicate that alteration in LV free wall function and changes in LV volume can directly effect RVDP through the myocardium.     

Localized endocrine conversion of ventricular cardiocytes in ventricular aneurysm

Atrial natriuretic peptide (ANP) is synthesized and stored in the atria of the heart, but not or at very low concentrations in the ventricles. We investigated the occurrence of ANP and its messenger RNA (mRNA) in human ventricular aneurysm where the cardiocytes were physically over-stretched. The techniques of light and electron microscopic immunocytochemistry, and RNA-RNA tissue in situ hybridization were employed. A large amount of ANP immunoreactivity was found in the cytoplasm of the cardiocytes in and around the aneurysm, but not in fibrous scar tissue or in the normal ventricles. Immunoelectron microscopy localized the immunoreactivity mainly to specific secretory granules in the cytoplasm of the cardiocytes. ANP mRNA was also detected in these cardiocytes. The abundance of both was much higher than that found in the hypertrophic ventricles of other types. The highest concentration of ANP immunoreactivity and of ANP mRNA was found in the cardiocytes located at the border zone. The quantities of both ANP and its mRNA decreased in cardiocytes more distant from the lesion. Our findings suggest that human ventricular cardiocytes in and around aneurysm can convert to produce large amounts of the endocrine peptide ANP. This ventricular endocrine conversion was localized and was probably caused by physical over-stretch of the cardiocytes.     

Passive ventricular constraint

Heart failure (HF) is a progressive degenerative and malignant syndrome with a large number of aetiologies including coronary artery disease, chronic hypertension, exposure to toxins, bacteria and viruses and in a significant percentage of HF patients, the causal mechanism is unclear. The HF trail of morbidity and mortality is well documented and is characterised by step-like periods of relative symptomatic stability, compensation, separated by decompensatory episodes. The homeostatic response to the decline in cardiac function is diverse and involves most organs. There is an increase in resting rate, intra-cardiac hormone production (catecholamines, aldosterone, etc.) and in particular structural changes occur with increased mass and dilatation (dilated cardiomyopathy, DCM). DCM is associated with decreased cardiac output, contractility and energy efficiency and an increase in pro-arrhythmia and conduction defects.

Kass et al. (Circulation 91(9) (1995) 2314) first demonstrated in patients who had undergone a dynamic cardio-myoplasty procedure, that, preventing further dilatation in DCM was beneficial and that the improved cardiovascular status was largely independent of muscle stimulation. We hypothesised that this outcome could be achieved by implanting a fabric cardiac support device around both ventricles to the AV junction. Subsequently, it was shown by us and others (Kass et al., 1995) (Cardiovasc. Res. 44(3) (1999) 549); (Ann. Thorac. Surg. 70(4) (2000) 1275) (in different animal models of DCM) that passive ventricular constraint prevented further dilatation, initiated left ventricular volume reduction and reversed the decline in ejection fraction, mitral valve integrity and left ventricular contractility, when compared with untreated controls. Subsequent European and North American clinical trials in patients with DCM of varying aetiologies have shown equal promise and an absence of device related complications (Circulation 104(12 Suppl. 1) (2001) I270); (Ann. Thorac. Cardiovasc. Surg. 7(5) (2001) 278).

The mechanisms behind this improvement have yet to be fully clarified however the support generated by the device upon the right and ventricular freewall would lower wall tension.

Not only is passive ventricular constraint a very promising treatment modality for heart failure and DCM it should provide a useful research tool for the study of the role of ventricular dilatation in the progression of heart failure.     

Bidirectional ventricular tachycardia: a hallmark of catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia is a familial cardiac arrhythmia that is related to RYR2 or CASQ2 gene mutation. It occurs in patients with structurally normal heart and causes exercise-emotion triggered syncope and sudden cardiac death. We present a 13 year-old girl with recurrent episodes of exercise-related syncope and prior history of sudden death in a first degree relative.     

Left ventricular false tendons

Left ventricular false tendons (LVFTs) are fibromuscular structures, connecting the left ventricular free wall or papillary muscle and the ventricular septum.There is some discussion about safety issues during intense exercise in athletes with LVFTs, as these bands have been associated with ventricular arrhythmias and abnormal cardiac remodelling. However, presence of LVFTs appears to be much more common than previously noted as imaging techniques have improved and the association between LVFTs and abnormal remodelling could very well be explained by better visibility in a dilated left ventricular lumen.Although LVFTs may result in electrocardiographic abnormalities and could form a substrate for ventricular arrhythmias, it should be considered as a normal anatomic variant. Persons with LVFTs do not appear to have increased risk for ventricular arrhythmias or sudden cardiac death.     

Redistribution in left ventricular regional flow following acute right ventricular pressure overload

The left ventricular dysfunction following acute pulmowary hypertension remains unexplained. We wondered if acute pulmonary hypertension could alter the transmural flow distribution within the left ventricular myocardium, independent of coronary flow and perfusion pressure. We used a canine preparation in which the left coronary system was perfused at constant flow and induced a two- to three-fold increase in pulmonary artery pressure by banding the pulmonary artery. Regional myocardial blood flow of the left coronary system was measured using radioactive microspheres, injected into the left coronary system before and after 10-30 min of banding of the pulmonary artery. The left ventricular subendocardial:epicardial ratio fell by 12 and 31% (p less than 0.05) of control value, 10 and 30 min, respectively, after banding of the pulmonary artery, the total flow to the left coronary system being kept constant. Left atrial mean pressure increased from 2.9 +/- 2.4 to 3.6 +/- 1.9 and 6.0 +/- 2.1 (p less than 0.05) following banding. The mechanism of the redistribution of coronary flow may relate to inappropriate vasodilation of the right septal myocardium with consequent relative left ventricular subendocardial hypoperfusion which might aggravate left ventricular ischemia in the presence of hypotension and hypoxia.     

Idiopathic fascicular ventricular tachycardia

Idiopathic fascicular ventricular tachycardia is an important cardiac arrhythmia with specific electrocardiographic features and therapeutic options. It is characterized by relatively narrow QRS complex and right bundle branch block pattern. The QRS axis depends on which fascicle is involved in the re-entry. Left axis deviation is noted with left posterior fascicular tachycardia and right axis deviation with left anterior fascicular tachycardia. A left septal fascicular tachycardia with normal axis has also been described. Fascicular tachycardia is usually seen in individuals without structural heart disease. Response to verapamil is an important feature of fascicular tachycardia. Rare instances of termination with intravenous adenosine have also been noted. A presystolic or diastolic potential preceding the QRS, presumed to originate from the Purkinje fibers can be recorded during sinus rhythm and ventricular tachycardia in many patients with fascicular tachycardia. This potential (P potential) has been used as a guide to catheter ablation. Prompt recognition of fascicular tachycardia especially in the emergency department is very important. It is one of the eminently ablatable ventricular tachycardias. Primary ablation has been reported to have a higher success, lesser procedure time and fluoroscopy time.     

A new semantic mining approach for detecting ventricular tachycardia and ventricular fibrillation

Accurately differentiating between ventricular fibrillation (VF) and ventricular tachycardia (VT) episodes is crucial in preventing potentially fatal misinterpretations. If VT is misinterpreted as VF, the patient will receive an unnecessary shock that could damage the heart; conversely, if VF is incorrectly interpreted as VT, the result will be life-threatening. In this study, a new method called semantic mining is used to characterize VT and VF episodes by extracting their significant characteristics (the frequency, damping coefficient and input signal). This newly proposed method was tested using a widely recognized database provided by the Massachusetts Institute of Technology (MIT) and achieved high detection accuracy of 96.7%. The semantic mining technique was capable of completely discriminating between normal rhythms and VT and VF episodes without any false detections and also distinguished VT and VF episodes from one another with a recognition sensitivity of 94.1% and 95.2% for VT and VF, respectively.