Diverse styles of submarine venting on the ultraslow spreading Mid-Cayman Rise.

Thirty years after the first discovery of high-temperature submarine venting, the vast majority of the global mid-ocean ridge remains unexplored for hydrothermal activity. Of particular interest are the world's ultraslow spreading ridges that were the last to be demonstrated to host high-temperature venting but may host systems particularly relevant to prebiotic chemistry and the origins of life. Here we report evidence for previously unknown, diverse, and very deep hydrothermal vents along the approximately 110 km long, ultraslow spreading Mid-Cayman Rise (MCR). Our data indicate that the MCR hosts at least three discrete hydrothermal sites, each representing a different type of water-rock interaction, including both mafic and ultramafic systems and, at approximately 5,000 m, the deepest known hydrothermal vent. Although submarine hydrothermal circulation, in which seawater percolates through and reacts with host lithologies, occurs on all mid-ocean ridges, the diversity of vent types identified here and their relative geographic isolation make the MCR unique in the oceans. These new sites offer prospects for an expanded range of vent-fluid compositions, varieties of abiotic organic chemical synthesis and extremophile microorganisms, and unparalleled faunal biodiversity--all in close proximity.

Pathological effects of alcohol septal ablation for hypertrophic obstructive cardiomyopathy.

BACKGROUND: The pathological effects and the mechanisms of action of intracoronary administration of ethanol for alcohol septal ablation (ASA) for the management of hypertrophic obstructive cardiomyopathy (HOCM) are unknown. METHODS: We examined surgical specimens and, in one case, autopsy specimens from four patients who underwent surgical septal myectomy 2 days to 14 months after unsuccessful ASA. RESULTS: Pathological examination early after ASA showed coagulative necrosis of both the myocardium and the septal perforator arteries. Affected arteries were distended and occluded by necrotic intraluminal debris, without platelet-fibrin thrombi. Late after unsuccessful ASA, excised septal tissue was heterogeneous, containing a region of dense scar, and adjacent tissue containing viable myocytes and interspersed scar. CONCLUSIONS: Intracoronary administration of ethanol in patients with HOCM causes acute myocardial infarction with vascular necrosis. The coagulative necrosis of the arteries, their distension by necrotic debris and the absence of platelet-fibrin thrombi distinguish ethanol-induced infarction from that caused by atherosclerotic coronary artery disease. The direct vascular toxicity of ethanol may be an important aspect of the mechanism of successful ASA.

Effect of electrode position and gel-application technique on predicted transcardiac current during transthoracic defibrillation.

STUDY OBJECTIVE: In transthoracic defibrillation, the American Heart Association (AHA) recommends wide separation of electrodes and avoidance of gel smearing between electrodes. Few data support this recommendation. Our objective was to determine the importance of electrode placement and gel-application technique on transcardiac defibrillation current and the effect of changes caused by postexercise vasodilation and sweating. METHODS: Our subjects were 10 normal adults, 5 men and 5 women, who ranged in age from 22 to 48 years. We determined interelectrode impedance (Z) using a validated test-pulse method that does not require shock delivery. Electrode placement/gel-application techniques were varied among four types: (1) AHA-recommended technique (apex-to-anterior electrode placement, no smearing of gel between electrodes); (2) parasternal-to-anterior placement, electrodes within 2 cm of each other, no smearing of gel between electrodes; (3) parasternal-to-anterior placement, electrodes within 2 cm of each other with smearing of gel between electrodes (worst-case scenario); and (4) apex-to-anterior placement, smearing of gel between electrodes. To assess the effect of cutaneous vasodilation and sweating on interelectrode impedance, we repeated these measurements after the subjects performed 12 to 18 minutes of treadmill exercise. The ratio of predicted transcardiac current of the AHA technique to that of the nonstandard technique was estimated with this formula: square root of Z, non-standard technique divided by square root of Z, AHA technique. RESULTS: Resting interelectrode impedance declined 38% from 58 +/- 10.3 omega (AHA-recommended technique) to 36 +/- 7.6 omega (electrode paddles adjacent, gel smeared between) (P < .01). Predicted transcardiac current ratio was reduced to .78 +/- .09 (P < .01), a 22% reduction. We noted no change in the results after exercise. CONCLUSION: Adjacent placement of electrodes and smearing of gel between electrodes creates a low-impedance pathway along the chest wall, which shunts current away from the heart. Thus improper application of electrodes and gel substantially degrades transcardiac current and may result in failed defibrillation. Sweating and vasodilation did not cause a similar problem.

Overlapping sequential pulses. A new waveform for transthoracic defibrillation.

BACKGROUND: A directionally changing shock electrical vector could facilitate defibrillation by depolarizing myocytes with different orientations vis-à-vis the shock field. Such a changing vector can be achieved by a new waveform for transthoracic defibrillation: overlapping sequential pulses. Our purpose was to evaluate this waveform. METHODS AND RESULTS: Ventricular fibrillation was induced in closed-chest dogs. Single and overlapping truncated exponential waveform pulse shocks were then administered from self-adhesive chest electrodes. Single pulse (control) shocks were 7.5-millisecond duration, while the sequential overlapping pulse shocks, using two different pathways, consisted of two pulses, each 5.0-millisecond duration; the second pulse began 2.5 milliseconds after the start of the first pulse and ended 2.5 milliseconds after the end of the first pulse. Thus, the total duration of the sequential overlapping shock was 7.5 milliseconds. During the overlap phase (2.5 milliseconds), the electrical vector orientation is the summation of the individual vectors. Two different electrode placements and corresponding electrical vector orientations were studied: group 1 (n = 14), left lower chest to right upper chest (pulse 1), overlapped by right lower chest to left upper chest (pulse 2), with the sequence then reversed; and group 2 (n = 11), left chest to right chest (pulse 1) overlapped by dorsal (vertebral column) to ventral (sternum) (pulse 2) with the sequence then reversed. At voltages equivalent to energies of 50, 100, and 150 J, the sequential overlapping pulse shocks achieve higher success rates than the single pulse shocks: At the low energy, 50 J, single pulse shock success rates were 0% (group 2) and 14% (group 1), while the overlapping pulse shocks achieved success rates of 39% (group 2) and 55% (group 1) (P < .05). Similarly, at the highest energy tested, 150 J, single pulse shock success rates were 45% (group 2) and 61% (group 1), while the overlapping pulse shock success was 91% (group 2) and 95% (group 1) (P < .05). In a third group of dogs (n = 3), intracardiac plunge electrodes placed orthogonally in the septum showed that the orthogonal components of intracardiac voltage gradient change varied markedly during the three phases of the sequential overlapping shocks, demonstrating the changing direction of the net electrical vector as the shock proceeded. In a fourth group of dogs (n = 5), short-duration (2.5-millisecond) single pulse shocks were compared with longer 7.5-millisecond single pulse shocks and with the sequential overlapping pulse shocks, all at equivalent energies. Despite substantially higher current flow, the 2.5-millisecond-duration single pulse shocks were not more effective than 7.5-millisecond single pulse shocks, and both 2.5- and 7.5-millisecond duration single pulse shocks had markedly inferior success rates compared with the sequential overlapping pulse shocks. CONCLUSIONS: Sequential overlapping pulse shock waveforms facilitate defibrillation compared with single pulse shocks of the same total energy. This is due at least in part to the changing orientation of the electrical vector during the multiple pulse shock.