Tachycardia definition

The bradycardia-tachycardia ("sick sinus") syndrome is a definite contraindication to the use of lithium because the ion further depresses the sinus node. T-wave flattening is often observed on the ECG but is of questionable significance. 

According to the researchers, nearly half of the adverse events definitely, probably, or possibly caused by ephedra were cardiovascular side effects. The most common cardiovascular side effect was hypertension, or high blood pressure. Other reported cardiovascular events were palpitations, tachycardia (an abnormally fast heartbeat), stroke, and seizures. The researchers stated that 10 of the adverse events definitely, probably, or possibly caused by ephedra resulted in death, and 13 of the events caused permanent disability. In one-fifth of the cases, there was not enough evidence or information about the incident, and the remaining complications were not related to ephedra. 

Flecainide slows conduction in all cardiac cells including the anomalous pathways responsible for the Wolff-Parkinson-White (WPW) syndrome. Together with encainide and moricizine, it underwent clinical trials to establish if suppression of asymptomatic premature beats with antiarrhythmic drugs would reduce the risk of death from arrhythmia after myocardial infarction. The study was terminated after preliminary analysis of 1727 patients revealed that mortality in the groups treated with flecainide or encainide was 7.7% compared with 3.0% in controls. The most likely explanation for the result was the induction of lethal ventricular arrhythmias possibly due to ischaemia by flecainide and encainide, i.e. a proarrhythmic effect. In the light of these findings the indications for flecainide are restricted to patients with no evidence of structural heart disease. The most common indication, indeed where it is the drug of choice, is atrioventricular re-entrant tachycardia, such as AV nodal tachycardia or in the tachycardias associated with the WPW syndrome or similar conditions with anomalous pathways. This should be as a prelude to definitive treatment with radiofrequency ablation. Flecainide may also be useful in patients with paroxysmal atrial fibrillation. 

Systemic effects, such as dizziness, tachycardia, agitation, nausea, tremor, syncope, seizures, and bronchos-pasm, are a definite risk with local anesthesia in a vascular area. A wide range of patients present for dental surgery, and it is important that an adequate medical history be taken and accurate doses calculated on an individual basis. Low concentrations of adrenahne should be used. 

Many cases of serious adverse effects and even fatalities have been reported that were linked with ephedra or ephedrine administration over the last 10 years. Haller and Benowitz published a review of 140 reports of adverse events related to the use of ephedra alkaloids that were submitted to the FDA between June 1997 and March 1999. Using standardized rating system for assessing causation, 31% of the cases were considered to be definitely or probably related to the use of ephedra alkaloid-containing supplements, and another 31% were deemed to be possibly related. Among these adverse events, 47% involved in cardiovascular symptoms and 18% involved the CNS. Hypertension was the most frequent adverse effect, followed by palpitations, tachycardia, or both stroke and seizures. Ten events led to death and 13 cases produced permanent disability. 

Haller and Benowitz evaluated 140 reports of ephedra-related toxicity and concluded that 31% of the cases were definitely related to ephedra toxicity and a further 31% were possibly related 47% of reports of ephedra toxicity involved cardiovascular problems and 18% involved problems with the CNS. Hypertension was the single most frequent adverse reaction, followed by palpitation, tachycardia, stroke and seizure. Ten events resulted in death and 13 events caused permanent disability. The authors concluded that use of dietary supplements that contains ephedra may pose a health risk. ... 

The common ventricular arrhythmias include (1) premature ventricular complexes (PVCs), (2) ventricular tachycardia, and (3) ventricular fibrillation. Again, these arrhythmias may result in a wide variety of symptoms. PVCs often cause no symptoms or only mild palpitations. Ventricular tachycardia may be a life-threatening situation associated with hemodynamic collapse or be totally asymptomatic. Ventricular fibrillation, by definition, is an acute medical emergency necessitating cardiopulmonary resuscitation (CPR). 

Of the other 9 patients, 3 had immediate and definite ST-T wave changes, and the remaining 6 had no demonstrable changes. There are other reports of this interaction, " including one that describes sinus tachycardia and atrial flutter in 6 out of 18 patients taking digoxin after they were given pancuronium. ... 

Ventricular tachycardia (VT) is the result of uncontrolled electrical activity in the ventricle. This activity may be coordinated or uncoordinated. The definitive therapy for Ventricular is external stimulation by an electric field sufficiently large to reset the electrical activity of most ventricular cells. This ends the previous (uncontrolled) electrical activity and allows the reestablishment of normal cardiac activity. As explained earlier, this requires depolarization of a critical mass of tissue by a high-voltage discharge. When high-voltage therapy is delivered, an attempt is made to synchronize the delivery with a detected R-wave. A synchronized shock is termed cardioversion, whereas an unsynchronized shock is termed defibrillation because VF has no coherent electrical activity, and therefore no basis for synchronization (Figure 15.6). 

CAST-11 compared moricizine with placebo. The protocol for the CAST-11 was modified in an attempt to enroll patients more likely to experience serious arrhythmias and to observe for early risk of antiarrhythmic drugs. The qualifying ejection fraction was lowered to < 0.40, a higher dose of moricizine could be used, and the definition of disqualifying ventricular tachycardia was changed to allow patients with more serious arrhythmias to be entered into the trial. CAST II was subsequently terminated prematurely because patients treated with moricizine had an increased cardiac mortality rate during the first... 

Frequent shocks can occnr for several reasons. Most commonly they are due to repetitive episodes of supraventricular tachycardia or ventricular tachycardia, or a lead/lCD sensing problon. The definition of frequent shocks varies among physicians and patients, but more than three shocks within 24 h are probably appropriate and this situation is frequently referred to as electrical storm. Freqnent shocks are associated with depression and reduced mental health. The canses and evaluation of a patient with frequent shocks are summarized in Table 20.6. 

One of the eventual results of lead - induced inhibition of enzymes in the heme synthesis pathway is anemia which can be asymptomatic if mild but associated with a wide array of symptoms including dizziness, fatigue, and tachycardia when more severe. Studies have indicated that lead levels as low as 50 xg/dl can be associated with a definite decreased hemoglobin, although most cases of lead - induced anemia, as well as shortened red-cell survival times, occur at lead levels exceeding 80 xg/dl. Inhibited hemoglobin synthesis is more common in chronic cases whereas shortened erythrocyte life span is more common in acute cases. 

In children, evaluate bradycardia and tachycardia in context. For example, bradycardia (less than 90 beats/minute) may occur in a healthy infant during sleep tachycardia may be a normal response when a child is crying or otherwise upset. Keep in mind that, because HR varies considerably from the neonate to the adolescent, one definition of bradycardia or tachycardia can t fit all children. 

Aronski et al. (45 ) studied systolic time intervals and peripheral blood flow in 12 patients after induction of anaesthesia with 0.05 ml/kg body weight Althesin and concluded that the drug has a definite cardio-depressive action. In another series of 220 patients (46 ) tachycardia and hypotension were seen in 35 and 25% of cases respectively. The respiratory depressant effect of the drug was related to the speed of injection. Muscle tremors were absent when Althesin was given by intravenous infusion. Even convulsions after Althesin have been described, immediately after the injection (4 C) or, in the case of less rapid injection, after some delay (48C). The slow injection of Althesin can indeed reduce the incidence of aU its side effects, as was shown in a comparison between 2 groups of 30 patients in which differing rates of administration were employed (49C). 

If a definitive diagnosis of supraventricular tachycardia or VT can t be established, treatment should be guided by whether cardiac function is adequate (ejection fraction above 40%). 

---