Toyomi Sano

Acute Effects of Elevation of Coronary Sinus Pressure

The acute physiologic effects of the aorta to coronary sinus anastomosis of Beck have been studied. The evidence presented shows that arterialization of the coronary sinus results in a small retrograde flow from the sinus through capillaries into the occluded artery and that such retrograde flow supplies from 14 to 25 per cent of the normal myocardial oxygen requirement. It is suggested that this is insufficient to maintain normal myocardial contraction, but probably prevents ventricular fibrillation. However, when the sinus is arterialized in the presence of normal or reduced coronary flow electrocardiographic and coronary inflow data show that there is myocardial anoxia. This is probably due to the restriction in capillary outflow and results in an expansion of the coronary vascular bed.

P vector loop in health and disease as studied by the technique of electrical dissection of the vectorcardiogram (differential vectorcardiography).

Abstract 1. The isolated P vector loops were obtained by the technique of electrical dissection (differential vectorcardiography), in 81 cases: 16 normal cases; 15 cases with practically normal P waves; 23 cases with left atrial hypertrophy; 3 cases with borderline left atrial hypertrophy; 1 case with probable right atrial hypertrophy; 14 cases with right atrial hypertrophy; 5 cases with combined atrial hypertrophy; and 4 cases with ectopic origin of the P wave. 2. Exclusive of P vector loops of ectopic origin, the direction of inscription of the P vector loop, in both healthy and diseased patients was principally counterclockwise in the frontal and horizontal planes, and clockwise in the sagittal plane. 3. The normal P loop was small, closed, or slightly open, and directed almost vertically inferiorly. The P loop of left atrial hypertrophy was larger and more opened, and the maximal vector was directed posteriorly, inferiorly and left-ward. The P loop of right atrial hypertrophy was the largest and most widely opened and its maximum vector was directed anteriorly and inferiorly. 4. The Ta vector was located about 180 degrees from the maximal P vector in hypertrophy. The physiologic significance of the morphology of the P vector loop was discussed. 5. The P vector loop is often helpful clinically in the differentiation between right and left atrial hypertrophy, when standard electrocardiograms are equivocal. 6. he superiority of the isolated P vector loops lies in the ease with which deviations from the normal pattern can be detected.

Dissection of the vectorcardiogram: Differential vectorcardiography

Abstract A practical selective dissector apparatus has been constructed and has been used with commericially available equipment to separate and record the component loops of the vectorcardiogram (P, QRS, ST-T loops).

Demonstration of bidirectional dual A-V nodal pathways in the same patient.

In a patient with documented paroxysmal junctional tachycardia (PJT) electrophysiologic studies were performed using an extrastimulus technique. At an A1-A2 interval of 360 msec, atrial extrastimulus revealed sudden prolongation of an A2-H2 interval from 370 to 540 msec and PJT ensued. This finding was consistent with antegrade dual A-V nodal pathways. On the other hand, at a V1-V2 interval of 540 msec, ventricular estrastimulus showed a jump in ventriculo-atrial (V-A) conduction time with evidence of delay in the A-V node from 285 to 565 msec and a ventricular echo followed. This finding was consistent with retrograde dual A-V nodal pathways. Mechanisms of bidirectional dual A-V nodal pathways are discussed.

The sino-atrial connection and wandering pacemaker

Summary In the rabbit heart the transitional tissue between the sinus nodal tissue and the ordinary atrial muscle fibers has a fairly wide distribution at the origin of the superior vena cava. From the functional point of view the bridge-like extension of this tissue from the sinus node to the crista terminalis was found to be the only normal route of the excitation wave as a result of a histological study after cutting muscle pathways around the node and checking the changes in the transmission of the excitation by means of two microelectrodes. Preparations of the ring-like structure composed of the crista terminalis and its extention often showed spontaneous activity and the point of earliest excitation occasionally showed a prominent slow diastolic depolarization. Evidence has been presented that the pacemaker actually wandered down the crista terminalis, when acetylcholine was added. From these findings it was presumed that in human subjects the wandering pacemaker, especially when it appears to shift gradually, starts to shift from the sinus node through the bridgelike extention cranially to the crista terminalis, continues down the crista terminalis to the A-V node, and takes the same route in the opposite direction.

The U vector loop in normal and various abnormal states as studied by the summation method

Summary Employing a summation method with a computer, the U vector loop can be obtained in a reproducible and reliable way. In this study we found that the U main vector loop in normal subjects was directed anteriorly, inferiorly and mostly slightly to the left. In right bundle branch block, Wolff-Parkinson-White syndrome type A, and right ventricular hypertrophy, the U main vector was directed more to the left than normal. In left bundle branch block, Wolff-Parkinson-White syndrome type B and left ventricular hypertrophy, it was directed to the right. These findings favor a speculation that the U vector originates from the repolarization of the last repolarized part of the ventricle. In anterior myocardial infarction and angina pectoris showing ST-T change in the electrocardiogram (ECG), the U main vector was directed to the right and anteriorly. In inferior myocardial infarction it was within normal limits on the average but it was shifted upwards in some cases. These findings suggest that, in myocardial infarction, injury or ischemia, the U vector was modified in direction by the local delay of repolarization, provided that the exploring electrodes are close enough to record the local changes.

Electrophysiological effects of lactates in mammalian ventricular tissues

Effects of excessive lactates on electrophysiological parameters of Purkinje and ventricular muscle fibers, excised from dog hearts, were studied by the microelectrode technique. The application of 60mM-lactic acid produced the following changes in membrane potentials in both tissues: slight depolarization of resting potentials of 7 to 8 mV; decrease in the max.dV/dt of action potentials by an average of 10% from the control value; and shortening of action potential durations as well as of effective refractory periods by 17%. These effects appeared earlier in the Purkinje fibers than in the ventricular muscle fibers. The voltage dependence, max.dV/dt, was not changed after the lactate perfusion. This pointed to the depolarization of the resting potential as a cause of the decrease in the max.dV/dt of action potentials. In the Purkinje fibers, slow diastolic depolarization became manifest after the lactate application. Excessive lactates moderately depressed the slow response activity in both tissues. The perfusion of 60 mM-Na lactate had essentially similar effects in both tissues. In the ventricular muscle fibers, the voltage clamp experiments revealed that excessive lactate decreased the slow inward current and barely affected the steady-state K current. The results indicate that excessive lactates promote conditions likely to lead to a re-entry into the ventricle and, at the same time, to enhance the ectopic impulse formations in ventricular conducting tissues.

Depolarization phase of the spatial velocity electrocardiogram in normal and ventricular overloading

Summary The depolarization phase of the spatial velocity electrocardiogram was studied in normal subjects and patients with right and left ventricular overloading, and significant differences were found among them. The normal pattern consists usually of four spikes, ξ, ϱ 1 , ϱ 2 and σ, and of three nadirs between them, ξ e , ϱ m and σ i , which showed common features as follows: 1/2 ϱ 2 ≤ ϱ 1 ≤ ϱ 2 , ϱ m ≥1/3 ϱ 1 , ξ≤1/3 ϱ 1 , ξ e ≥1/3 ξ, σ≤1/3 ϱ 2 , σ i ≥1/3 σ, ξϱσ duration ≤100 msec, interval between the peak of ϱ 1 and ϱ 2 ≤ 20 msec, ξ duration ≤20 msec, and σ duration≤40 msec. The spatial velocity electrocardiogram of left ventricular overloading showed one or more of the following features: ϱ 1 was larger than ϱ 2 , ϱ m was less than a third of ϱ 1 , splitting between ϱ 1 and ϱ 2 was deeper and wider than normal ranges, ϱ 1 showed splitting, or both ξ and σ were absent. Left ventricular volume overloading could be largely differentiated from left ventricular pressure overloading by a marked tendency of a deep ϱ m with a prolonged interval between the peak of ϱ 1 and ϱ 2 . In contrast the spatial velocity electrocardiogram of right ventricular overloading showed one or more of the following features: ϱ 1 was smaller than the half of ϱ 2 , σ was larger than a third of ϱ 2 , or splitting between ϱ 2 and σ was deeper and duration of σ was longer than normal ranges. Right ventricular volume overloading could be largely differentiated from right ventricular pressure overloading by a marked tendency of the deep σ i . with a prolonged duration of σ.

Electrical properties of the cells at the Purkinje fiber-myocardial cell region of the mammalian heart

Summary The action potential of the cell at the Purkinjemyocardial (P-M) cell region of the dog heart is composed of a spike and a dome separated by a distinct dip during orthodromic conduction, but this dip disappeared during antidromic conduction by extracellular stimulation. By intracellular stimulation, however, it was found that this dip did not disappear during antidromic conduction. The reason was that the Purkinje and myocardial fibers were excited almost simultaneously by extracellular antidromic stimulation probably because some small branches of the Purkinje fibers in the myocardial part were stimulated directly. Two types of action potential were obtained in the P-M region. In type A the spike was larger than the plateau and in type B the spike was smaller than the plateau. This feature became more marked when the frequency of the stimulus was increased. In type A the duration of the action potential including the spike component during orthodromic conduction was equal to that of the whole duration of action potential during antidromic conduction. In contrast, the duration of the action potential of type B, excluding the spike component during orthodromic conduction, was equal to the whole duration of the action potential during antidromic conduction. The rate of rise of the action potential was larger in the order of the Purkinje, type A, type B, and ventricular action potential. In type A the rate of the rise was larger during orthodromic than during antidromic conduction by extracellular stimulation. In contrast, in type B the rate of the rise was larger during antidromic conduction than during orthodromic conduction. This suggested that its increasing or decreasing mechanism during orthodromic conduction is different from that during antidromic conduction. Considering all of these features, it was presumed that both type A and type B were obtained from the Purkinje fiber portion of the P-M junction and type B was closer to the junction.

Properties of the fibers in the pathways along the anterior and posterior portions of the left A-V ring

A comparison was made of the electrophysiological properties of the fibers between the previously reported conduction pathways from the left atrium to the right atrium and to the ventricle (left A-V ring pathways) and the ordinary atrial muscle, using perfused isolated rabbit hearts. Each fiber within these pathways showed action potential with a well-developed plateau phase. The plateau phase of these action potentials was distinctly shortened by an infusion of 1 x 10-6 g/ml of acetylcholine. When the heart was perfused by Tyrode solution with 15 mM KCl, the trans-membrane potential of the ordinary atrial muscle fiber showed a decrease of resting potential and of amplitude of action potential. The fibers within these pathways, however, were more resistant to the high potassium solution than the ordinary atrial fibers. A slow diastolic depolarization was observed in the fibers of the pathway when 1-isoproterenol (1 x 10-5 g/ml) was applied locally. These findings suggest that the fibers within the left A-B ring pathways possess similar electrophysiological properties to the specialized fibers in the atria.