Unexpected Discharge from an Implanted Automatic Defibrillator

The occurrence of inappropriate discharge from an implanted cardioverter-defibrillator is reported. The device was triggered by an episode of induced nonsustained ventricular tachycardia, and the shock was delivered 10 sec after spontaneous termination of the arrhythmia.
This observation demonstrates that unexpected discharges from an implanted cardiaverter/defibrillator can occur while the patient is asymptomatic. In order to avoid such an adverse effect, improvement of the detection system of the device is advisable.     

Supernormal Conduction in the Left Bundle Branch Unmasked by the Linking Phenomenon

This presentation reflects a case of phase-3 left bundle branch block (LBBB). Analysis reveals that relatively early QRS complexes are wide, whereas beats occurring later than a critical time are narrow. There are, however, two unexpected phenomena: (1) an overlap occurs between the range of R-R intervals resulting in normal intraventricular conduction and the range of R-R intervals resulting in LBBB pattern. Complexes that follow a wide beat are often wide although they are associated with relatively long R-R intervals, whereas complexes that follow a normal beat tend to be normal even after relatively short R-R cycles. This is due to concealed retrograde penetration of the bundle branch that is blocked in anterograde direction (the so-called linking phenomenon). (2) Some early supraventricular impulses, paradoxically, resulted in normal intraventricular conduction. The phenomenon is a manifestation of supernormal LBB conduction, and only occurs following a wide QRS complex associated with retrograde activation of the LBB. The linking phenomenon reveals or unmasks the supernormal phase of LBB conduction. Following a retrograde and delayed activation of the LBB, the refractory period of the bundle branch is postponed, in such a way that a supraventricular impulse is allowed to occur during the early phase of supernormal conduction.     

Synthesis of peptide-immunogens corresponding to amino acid sequences from human histocompatibility class II membrane glycoproteins

Six peptides with amino acid sequences of human histocompatibility Class II membrane glycoproteins were synthesized by conventional solution methods. Five peptides were prepared by stepwise procedures from the carboxyterminus. The sixth was synthesized by fragment condensation (5 + 10 coupling). Antibodies to synthetic peptides were then used to locate exposed and buried regions in the membrane glycoproteins.     

The Replacement of the Ascending Aorta and Aortic Valve with a New Design Composite Graft: A Six-Year Experience

The problems encountered in coronary artery reattachment when the ascending aorta and aortic valve are replaced with a composite graft induced Gallucci and one of the authors to develop a new aortovalvular prosthesis in clinical practice. The unique transverse ovoidal shape of this graft is intended to conform to the natural aortic root and facilitate the coronary anastomoses and minimize bleeding. We present our 6-year experience with 56 patients operated upon with this prosthesis. In all patients we were able to connect the coronary arteries directly to the graft without complications including hemorrhage or distortion of the coronary ostia. The survivors were evaluated with chest X ray, two-dimensional echocardiography, and conventional or digital subtraction angiography to detect the presence of pseudoaneurysms at the site of the coronary anastomosis, reported by others that have used the composite graft technique. The notable absence of this complication in our patients at a mean follow-up of 41 months (range 3-71) documents that this ovoidal composite graft is a reliable tool in the treatment of aortic root pathology.     

The VITA Project: C677T mutation in the methylene-tetrahydrofolate reductase gene and risk of venous thromboembolism

We evaluated the hypothesis that a common polymorphism of the methylenetetrahydrofolate reductase gene (C677T), which results in increased levels of plasma homocysteine, may be a putative risk factor for venous thromboembolism (VT). Sixty-five cases of VT and 130 controls, both identified within the framework of an epidemiologic survey on thrombophilia, the Vicenza Thrombophilia and Arteriosclerosis (VITA) Project, were genotyped for the mutation. No increased risk of VT was found in carriers of the mutation. We conclude that screening for the C677T mutation of the methylenetetrahydrofolate reductase gene should not be recommended in unselected patients with VT.     

Visualization of Pattern Flow in Abdominal Arteries by Transgastric Echocardiography After Aortic Dissection Repair

The persistence of false lumen after surgical repair of aortic dissection is frequent. This event has a negative impact on the prognosis and is secondary to the persistence of unrepaired entry sites and of dissected major aortic branches. We describe three cases in which visualization of a dissected celiac trunk with an anomalous flow pattern was possible with transesoghageal echocardiography. Two of these cases died in the early postoperative period and the echo findings were confirmed at necropsy. We suggest that visualization of anomalous pattern flow in the celiac trunk is of prognostic relevance because it plays a major role in mantaining the false lumen persistence and, therefore, should be part of the routine examination after surgical repair of aortic dissection.     

Emergency Cardiac Pacing for Severe Bradycardia

ALTAMURA, G., ET AL.: Emergency Cardiac Pacing for Severe Bradycardia. Our study included the treatment of transcutaneous cardiac pacing (TCP) in 32 patients: (A) 19 patients were treated in the emergency area for complete symptomatic AV block before endocavitary pacing; (B) five patients were in asystole following DC shock or out-of-hospital cardiac arrest; and (C) eight patients were affected by bifascicular block undergoing emergency surgery and were treated in order to prevent complete AV block. Two transcutaneous stimulators were used. PaceAid-CRC model 50/52 with 20-msec pulse width; the electrodes were positioned on the V, ECG position and on the back. Results: in all but two patients, it was possible to obtain stable cardiac capture; in one patient arrived in hospital in asystole after prolonged cardiac arrest and in the other one was affected by complete AV block, TCP was ineffective. In groups A and B, TCP was maintained for a mean time of 15 minutes; in group C, TCP was tested in all patients, but performed in only one patient during surgery. Mean threshold was 81 mA. Stimulation was well tolerated in all but five patients. TCP is a reliable, noninvasive method that offers the possibility to initiate pacing within seconds and can be used by medical staff. In our opinion, it should be considered as the first choice emergency treatment of severe symptomatic bradycardia. In asystole, beneficial effects can be obtained only if TCP is performed early enough after the onset of arrhythmia.     

Molecular Biology of the Long QT Syndrome: Impact on Management

The long QT syndrome (LQTS) is a familial disease characterized by prolonged ventricular repolarization and high incidence of malignant ventricular tachyarrhythmias often occurring in conditions ofadrenergic activation. Recently, the genes for the LQTS linked to chromosomes 3 (LQT3), 7 (LQT2), and 11 (LQTl) were identified as SCN5A, the cardiac sodium channel gene and as HERG and KvLQTl potassium channel genes. These discoveries have paved the way for the development of gene-specific therapy for these three forms of LQTS. In order to test specific interventions potentially beneficial in the molecular variants of LQTS, we developed a cellular model to mimic the electrophysiological abnormalities of LQT3 and LQT2. Isolated guinea pig ventricular myocytes were exposed to anthopleurin and dofetilide in order to mimic LQT3 and LQT2, respectively. This model has been used to study the effect of sodium channel blockade and of rapid pacing showing a pronounced action potential shortening in response to Na⁺channel blockade with mexiletine and during rapid pacing only in anthopleurin-treated cells but not in dofetilide-treated cells. Based on these results we tested the hypothesis that QT interval would shorten more in LQT3 patients in response to mexiletine and to increases in heart rate. Mexiletine shortened significantly the QT interval among LQT3 patients but not among LQT2 patients. LQT3 patients shortened their QT interval in response to increases in heart rate much more than LQT2 patients and healthy controls. These findings suggest thatLQT3 patients are more likely to benefit from Na⁺ channel blockers and from cardiac pacing because they are at higher arrhythmic risk at slow heart rates. Conversely, LQT2 patients are at higher risk to develop syncope under stressful conditions, because of the combined arrhythmogenic effect of cate-cholamines with the insufficient adaptation of their QT interval. Along the same line of development of gene-specific therapy, recent data demonstrated that an increase in the extracellular concentration of potassium shortens the QT interval in LQT2 patients suggesting that intervention aimed at increasing potassium plasma levels may represent a specific treatment for LQT2. The molecular findings on LQTS suggest the possibility of developing therapeutic interventions targeted to specific genetic defects. Until definitive data become available, antiadrenergic therapy remains the mainstay in the management of LQTS patients, however it may be soon worth considering the addition of a Na + channel blocker such as mexiletine for LQT3 patients and of interventions such as K⁺ channel openers or increases in the extracellular concentration of potassium for LQTl and LQT2 patients.