Non-Synchronized Direct-Current Countershock in Cardiac Arrhythmias

One hundred and thirty-two direct-current shocks were administered to 82 patients in an attempt to convert supraventricular tachyarrhythmias. Sinus rhythm was restored in 74 patients. In at least seven instances the shock was delivered during the T wave. Ventricular fibrillation did not occur. One episode of ventricular tachycardia and one of third-degree heart block followed countershock and terminated spontaneously. Excessive digitalis was considered to be a contributing factor in these two arrhythmias. Non-synchronized countershock is considered a safe and effective method of converting atrial fibrillation and flutter.     

Cardiac Arrhythmias In Congenital Heart Diseases

Arrhythmias figure prominently among the complications encountered in the varied and diverse population of patients with congenital heart disease, and are the leading cause of morbidity and mortality. The incidence generally increases as the patient ages, with multifactorial predisposing features that may include congenitally malformed or displaced conduction systems, altered hemodynamics, mechanical or hypoxic stress, and residual or postoperative sequelae. The safe and effective management of arrhythmias in congenital heart disease requires a thorough appreciation for conduction system variants, arrhythmia mechanisms, underlying anatomy, and associated physiology. We, therefore, begin this review by presenting the scope of the problem, outlining therapeutic options, and summarizing congenital heart disease-related conduction system anomalies associated with disorders of the sinus node and AV conduction system. Arrhythmias encountered in common forms of congenital heart disease are subsequently discussed. In so doing, we touch upon issues related to risk stratification for sudden death, implantable cardiac devices, catheter ablation, and adjuvant surgical therapy.     

Immediate Effects of Intravenous Verapamil in Cardiac Arrhythmias

Verapamil was administered by intravenous injection to 181 patients with various cardiac arrhythmias. The automaticity of the cardiac pacemaker was slowed in sinus, idionodal, and idioventricular tachycardia. In atrial fibrillation the drug usually slowed the ventricular response and often made it regular. In some cases atrial flutter was converted to sinus rhythm, the ventricular response being reduced in the remainder. Conversion of paroxysmal supraventricular tachycardia to sinus rhythm was consistently achieved. A favourable response occurred in four patients in whom arrhythmias were associated with pre-excitation syndromes. There were no adverse clinical side effects.     

Sex-Based Differences in Cardiac Arrhythmias, ICD Utilisation and Cardiac Resynchronisation Therapy

Many important differences in the presentation and clinical course of cardiac arrhythmias are present between men and women that should be accounted for in clinical practice. In this paper, we review published data on gender differences in cardiac excitable properties, supraventricular tachycardias, ventricular tachycardias, sudden cardiac death, and the utilisation of implantable defibrillators and cardiac resynchronisation therapy. Women have a higher heart rate at rest, and a longer QT interval than men. They further have a narrower QRS complex and lower QRS voltages on the 12-lead ECG with more often non-specific repolarisation abnormalities at rest. Supraventricular tachycardias, such as AV nodal reentrant tachycardia, are twice as frequent in women compared with men. Atrial fibrillation, however, has a 1.5-fold higher prevalence in men. The triggers for idiopathic right ventricular outflow tract tachycardia (VT) initiation are gender specific, i.e. hormonal changes play an important role in the occurrence of these VTs in women. There are clear-cut gender differences in acquired and congenital LQTS. Brugada syndrome affects men more commonly and severely than women. Sudden cardiac death is less prevalent in women at all ages and occurs 10 years later in women than in men. This may be related to the later onset of clinically manifest coronary heart disease in women. Among patients who receive ICDs and CRT devices, women appear to be under-represented, while they may benefit even more from these novel therapies.     

Reduced Incidence of Cardiac Arrhythmias in Walkers and Runners

Purpose

Walking is purported to reduce the risk of atrial fibrillation by 48%, whereas jogging is purported to increase its risk by 53%, suggesting a strong anti-arrhythmic benefit of walking over running. The purpose of these analyses is to compare incident self-reported physician-diagnosed cardiac arrhythmia to baseline energy expenditure (metabolic equivalent hours per day, METhr/d) from walking, running and other exercise.

Methods

Proportional hazards analysis of 14,734 walkers and 32,073 runners.

Results

There were 1,060 incident cardiac arrhythmias (412 walkers, 648 runners) during 6.2 years of follow-up. The risk for incident cardiac arrhythmias declined 4.4% per baseline METhr/d walked by the walkers, or running in the runners (P = 0.0001). Specifically, the risk declined 14.2% (hazard ratio: 0.858) for 1.8 to 3.6 METhr/d, 26.5% for 3.6 to 5.4 METhr/d, and 31.7% for ≥5.4 METhr/d, relative to <1.8 METhr/d. The risk reduction per METhr/d was significantly greater for walking than running (P<0.01), but only because walkers were at 34% greater risk than runners who fell below contemporary physical activity guideline recommendations; otherwise the walkers and runners had similar risks for cardiac arrhythmias. Cardiac arrhythmias were unrelated to walking and running intensity, and unrelated to marathon participation and performance.

Conclusions

The risk for cardiac arrhythmias was similar in walkers and runners who expended comparable METhr/d during structured exercise. We found no significant risk increase for self-reported cardiac arrhythmias associated with running distance, exercise intensity, or marathon participation. Rhythm abnormalities were based on self-report, precluding definitive categorization of the nature of the rhythm disturbance. However, even if the runners’ arrhythmias include sinus bradycardia due to running itself, there was no increase in arrhythmias with greater running distance.     

Treatment of Cardiac Arrhythmias with Synchronized Electrical Counter-shock

Synchronized electrical countershock is an intriguing new method for the treatment of ectopic tachycardias. The authors applied this treatment to 20 patients with chronic atrial fibrillation and, in 17 patients, sinus rhythm was restored immediately. An additional four patients with atrial flutter were successfully converted to sinus rhythm. One patient developed a hemiplegia two weeks after cardioversion. No other untoward side effects were observed. In two patients with ventricular fibrillation electrical countershock terminated the arrhythmia. After successful cardioversion of atrial fibrillation, a maintenance dose of quinidine is given to help maintain sinus rhythm. In spite of this precaution, one-half of the patients reverted to atrial fibrillation within a month. The quinidine was administered for two to three days in advance of cardioversion; on this regimen, 10 of 34 patients reverted to sinus rhythm on quinidine alone and did not require countershock. The exact place of this treatment of cardiac arrhythmias has not yet been clearly defined.     

Significance of Potassium in Genesis of Arrhythmias in Induced Cardiac Ischaemia

Paired biopsy specimens from the right or left atrial appendage have been taken from patients undergoing cardiopulmonary bypass surgery after various periods of intermittent coronary artery occlusion and analysed for potassium, sodium, and chloride content, total tissue water, and extracellular fluid volume.Tissue potassium content is reduced after coronary artery occlusion, and potassium loss bears an apparently linear relationship to the duration of occlusion. After 150 minutes of occlusion the potassium content had decreased by nearly 50%.For the first 50 minutes of occlusion the myocardial cells swelled at the expense of the extracellular fluid volume. Thereafter there was movement of water in the opposite direction, with subsequent cell shrinkage.The loss of potassium and the alteration in cellular hydration exert profound effects on the calculated gradient of potassium across the cell membrane. This is discussed in relation to the arrhythmias and low cardiac output after myocardial ischaemia. An attempt to rationalize treatment is made.     

Use of Oxprenolol in Cardiac Arrhythmias Associated with Acute Myocardial Ischaemia

Oxprenolol, a new beta-receptor blocking drug with intrinsic sympathomimetic activity, was used to treat 63 episodes of cardiac arrhythmia occurring in 43 patients with acute myocardial infarction or myocardial ischaemia. The drug was most effective in abolishing ventricular ectopic beats and supraventricular tachycardia. The best method of administration was by continuous intravenous infusion and the most satisfactory bolus does was 6 mg. The main side effect was hypotension, which occurred in 59% of episodes of arrhythmia that had responded previously to intravenous administration. Oxprenolol was often effective in lignocaine-resistant arrhythmia. The two main advantages of oxprenolol over propranolol are the reduced likelihood of adversely affecting myocardial function and the diminished tendency to produce bronchospasm.