The Zone of Vulnerability to T Wave Shocks in Humans

Vulnerability to VF in Humans. Introduction: Shocks during the vulnerable period of the cardiac cycle induce ventricular fibrillation (VF) if their strength is above the VF threshold (VFT) and less than the upper limit of vulnerability (ULV). However, the range of shock strengths that constitutes the vulnerable zone and the corresponding range of coupling intervals have not been defined in humans. The ULV has been proposed as a measure of defibrillation because it correlates with the defibrillation threshold (DFT), but the optimal coupling interval for identifying it is unknown. Methods and Results: We studied 14 patients at implants of transvenous cardioverter defibrillators. The DFT was defined as the weakest shock that defibrillated after 10 seconds of VF. The ULV was defined as the weakest shock that did not induce VF when given at 0, 20, and 40 msec before the peak of the T wave or 20 msec after the peak in ventricular paced rhythm at a cycle length of 500 msec. The VFT was defined as the weakest shock that induced VF at any of the same four intervals. To identify the upper and lower boundaries of the vulnerable zone, we determined the shock strengths required to induce VF at all four intervals for weak shocks near the VFT and strong shocks near the ULV. The VFT was 72 ± 42 V, and the ULV was 411 ± 88 V. In all patients, a shock strength of 200 V exceeded the VFT and was less than the ULV. The coupling interval at the ULV was 19 ± 11 msec shorter than the coupling interval at the VFT (P < 0.001). The vulnerable zone showed a sharp peak at the ULV and a less distinct nadir at the VFT. A 20-msec error in the interval at which the ULV was measured could have resulted in underestimating it by a maximum of 95 ± 31 V. The weakest shock that did not induce VF was greater for the shortest interval tested than for the longest interval at both the upper boundary (356 ± 108 V vs 280 ± 78 V; P < 0.01) and lower boundary (136 ± 68 msec vs 100 ± 65 msec; P < 0.05). Conclusions: The human vulnerable zone is not symmetric with respect to a single coupling interval, but slants from the upper left to lower right. Small differences in the coupling interval at which the ULV is determined or use of the coupling interval at the VFT to determine the ULV may result in significant variations in its measured value. An efficient strategy for inducing VF would begin by delivering a 200-V shock at a coupling interval 10 msec before the peak of the T wave.     

Implantable Cardioverter Defibrillator Oversensing During Periods of Rate-Related Bundle Branch Block

ICD Oversensing During Rate-Related BBB. A patient with an implantable cardioverter defibrillator (ICD) and a dual chamber pacemaker experienced inappropriate ICD therapies only during periods of rate-dependent right bundle branch block. Analysis of both stored and real-time ICD electrograms was critical to correctly diagnosing the problem and offering a solution.     

Cytology of the Liver, Spleen and Peritoneum Obtained by Sheathed Brush During Laparoscopy

A sheathed cytology brush, fashioned to be used during laparoscopy, is described for brushing the surface of the liver, spleen and peritoneum. The method has had no morbidity or complication in 100 consecutive patients. and has been highly successful in obtaining diagnostic cytological material from malignant neoplasms involving the liver (94%) and peritoneum (100%). In two cases, biopsies of tumor nodules were nondiagnostic, while brush cytology definitively documented malignancy. Because the brushing induces minimal trauma and is quick and simple to perform, it is suggested that brush cytology be considered a supplement to needle and forceps biopsies during laparoscopy. The stainless steel sheath on the brush eliminates concern over loss of cytologic material during brush withdrawal.     

Safety Factor for Precordial Pacing: Minimum Current Thresholds for Pacing and for Ventricular Fibrillation by Vulnerable-period Stimulation

Temporary cardiac pacing by means of rapidly applied, precordial electrodes can be of great value in selected patients suffering cardiac arrest or profound bradycardia, post-defibrillation atrioventricular block, or digitalis intoxication. This study provides data pertaining to the safety of precordial pacing measured as the ratio of the minimum current required to induce ventricular fibrillation (VF) to the minimum current required to pace the ventricular myocardium. Single rectangular pulse stimuli having durations of 1–50 ms were evaluated. In 6 anesthetized dogs, a cutaneous electrode was centered over the shaved apex beat area of the left chest and paired with a larger electrode sutured to the right chest wall. Using a specially fabricated, synchronized, high-energy pulse generator, the "most vulnerable" time in the cardiac cycle at which the least current was required to induce VF with a single shock was identified. This current was compared to the much lower current required to pace the heart in the diastolic interval. While the current required to produce either fibrillation or pacing decreased as pulse duration increased, the safety factor (i.e., the ratio of fibrillation current to pacing current) remained nearly constant, averaging 12.6 for all pulse durations examined. That is, on the average, a stimulus of any given duration between 1 and 50 ms required at least 12 times the current required for pacing to produce ventricular fibrillation. We conclude that in normal canine hearts, the risk of inducing VF during precordial pacing is small.     

Aortic Dissection Masquerading as Systemic Disease--the Post-Dissection Syndrome

Three patients presented with a prolonged illness accompaniedby fever, weight loss, high ESR, neutrophilia, abnormal liverfunction tests, urinary abnormalities and, in one case, splinterhaemorrhages and impairment of renal function. Aortic dissectionwas diagnosed 3–12 weeks after the onset of the illness,and probably accounted for the entire syndrome. All abnormalitiesresolved spontaneously over the following months. There are few similar cases in the literature, and the syndromecould easily pass unrecognized. Aortic dissection should beconsidered as a possible cause of any systemic illness of suddenonset, but especially if there is an initial history of chestor abdominal pain, or evidence of previous hypertension or otherrisk factors.     

Six-month study of the effect of a dentifrice containing zinc citrate and triclosan on plaque, gingival health, and calculus

Abstract – In two previous studies gingival health was maintained for at least 12 months by a dentifrice containing zinc citrate and triclosan. The aims of the present study were to determine if a zinc/triclosan dentifrice would stabilize gingival health if a lower concentration of zinc was used and to investigate its effect on the formation of calculus. 101 men and women were given oral hygiene instruction and their teeth were professionally cleaned. Two balanced groups were then formed, based on the prestudy levels of gingival bleeding and calculus. One group used the zinc/triclosan dentifrice for 6 months, while the other used a control. Results were assessed after 3 months and 6 months. Following the oral hygiene instruction, plaque and gingival bleeding were assessed at the end of the 4-wk period preceding the experimental phase, and both had been reduced. This improvement was not maintained by the control group, whereas the test group exhibited significantly lower plaque levels and a higher standard of gingival health throughout the 6 months. After 3 months, levels of calculus in the control group had returned to prestudy levels. At both the 3- and 6-month assessments, significantly less calculus was observed in the test group. The improved plaque control, stabilized gingival health, and reduced calculus formation support the conclusion that a dentifrice containing 0.5% zinc citrate and 0.2% triclosan can contribute to oral care.     

Implantable Defibrillator Diagnostic Storage Capabilities: Evolution, Current Status, and Future Utilization

There has been a rapid and significant evolution in the stored diagnostic information available from implantable cardioverter defibrillatars (ICDs). The diagnostic information available in current generation ICDs has greatly enhanced the clinicians' ability to determine the rhythm triggering device therapy as well as to identify potential problems with the ICD system. Furthermore, this information may be useful in identifying triggers of ventricular arrhythmias in patients at high risk for sudden death. The history, evolution, value, and limitations of the stored diagnostic capabilities of implantable defibrillators are discussed.