Sen Ji

Mechanosensitivity of the Cardiac Muscarinic Potassium Channel A NOVEL PROPERTY CONFERRED BY Kir3.4 SUBUNIT

Muscarinic potassium channels are heterotetramers of Kir3.1 and other Kir3 channel subunits and play major roles in regulating membrane excitability in cardiac atrial, neuronal, and neuroendocrine tissues. We report here that rabbit atrial muscarinic potassium channels are rapidly and reversibly inhibited by membrane stretch, possibly serving as a mechanoelectrical feedback pathway. To probe the molecular basis for this phenomenon, we heterologously expressed heteromeric Kir3.1/Kir3.4 channels in Xenopusoocytes and found that they possess similar mechanosensitivity in response to hypo-osmolar stress. This could be attributed in part, if not exclusively, to the Kir3.4 subunit, which reproduced the mechanosensitivity of the heteromeric channel when expressed as a homomeric channel in oocytes. Kir3.4 is the first stretch-inactivated potassium channel to be identified molecularly. Physiologically, this feature may be important in atrial volume-sensing and other responses to stretch.

Beyond coronary sinus angiography: the value of coronary arteriography and identification of the pericardiophrenic vein during left ventricular lead placement.

Objective: The purpose of this study was to define the role coronary arteriography (venous phase) for improving the success of left ventricular (LV) lead implantation and to define the value of identifying the pericardiophrenic vein for optimal LV lead placement in biventricular (bi‐v) device implantation.

Left Ventricular Endocardial Lead Placement Using a Modified Transseptal Approach

Coronary sinus cannulation and placement of left ventricular (LV) leads can be difficult. Occasionally alternative approaches are required. We report the first case of a modified transseptal LV endocardial lead placement via the left axillary vein for cardiac resynchronization. (J Cardiovasc Electrophysiol, Vol. 15, pp. 234‐236, February 2004)

Electrophysiological characterization of cardiac veins in humans

AbstractBackground: The coronary sinus is a complex structure with a surrounding myocardial coat and muscle bundles that course within it. The purpose of this study was to evaluate the electrical activity of the coronary sinus (CS), great cardiac vein (GCV) and related structures, such as the Vein of Marshall (VOM). Methods and Results: Data obtained from adult (n = 114) and pediatric patients (n = 16) were analyzed. The width of atrial electrograms (EGMs) within the CS at a basic pacing cycle length of 600 ms was 46 ± 7.4 ms (mean ± SD) vs. 29.7 ± 6.3 ms in the GCV (p < 0.01). With decremental pacing the width of the EGM within the CS at 300 ms increased to 66.6 ± 8.5 ms (p < 0.1 compared to CS EGM at pacing cycle length of 600 ms). The width of the EGM within the GCV increased from 29.7 ± 6.3 ms at a pacing cycle length of 600 ms to 34.6 ± 6.0 at 300 ms (p = NS). There were no significant differences in the atrial EGM width between CS and GCV in the pediatric patients. Conclusions: We conclude that atrial electrograms are wider in the CS but not in the GCV. This finding can be explained by the presence of a myocardial coat around the CS. The rate response characteristics of the atrial electrograms within the CS are consistent with a lack of tight coupling between muscle bundles and the CS musculature. Further, the absence of such differences in pediatric patients could partly explain relative differences in types of supraventricular arrhythmias seen in different age groups.

Oxygen Free Radicals in the Pathophysiology of Myocardial Ischemia/Reperfusion

In the setting of an acute myocardial infarction, there is a limited time window after the onset of coronary artery occlusion after which reperfusion is associated with irreversible cardiac injury. Cellular morphology by light and electron microscopy may be only mildly abnormal immediately before reperfusion, but becomes markedly distorted with sarcolemmal disruption, swollen mitochondria, and contraction band necrosis within minutes of reperfusion (Jennings and Ganote, 1974). It has been traditionally held that the major component of this irreversible injury occurs during the ischemic period itself, and that reperfusion only unmasks the latent damage (Braunwald and Kloner, 1985). However, it has become apparent that the conditions of reperfusion can significantly influence ultimate recovery of function (Buckberg, 1986; Kloner et al., 1989), consistent with the possibility that the act of reperfusion may convert potentially reversible ischemic injury into irreversible damage. In addition to this type of irreversible reperfusion injury, reperfusion after shorter durations of ischemia is associated with reversible myocardial dysfunction, or stunning, in which contractile and metabolic abnormalities may persist for hours to weeks before eventually recovering (Braunwald and Kloner, 1982). It has been shown that modifying the conditions of reperfusion can also reduce the severity of stunning (Kitakaze et al., 1988).

One tachycardia with two entrainment responses: What is the mechanism?

The patient presented for electrophysiology study and ablation for a history of narrow complex tachycardia. Both typical and atypical atrioventricular nodal reentrant tachycardia (AVNRT) were induced. For the atypical AVNRT, two different entrainment responses were recorded owing to different timing in delivering the ventricular pacing train.