[Influence of the permeability of the artery responsible for the infarction on the variability of heart rate and late potentials. Its importance in the risk stratification after myocardial infarction]. / Influencia de la permeabilidad de la arteria responsable del infarto sobre la variabilidad de la frecuencia cardíaca y potenciales tardíos. Su importancia en la estratificación del riesgo postinfarto de miocardio.

The use of the heart rate variability for the study of the Autonomic nervous system has been well established. We analyzed late potentials and heart rate variability in 29 control patients and in 102 consecutive patients with a first myocardial infarction. The data obtained were analyzed with both, the medical treatment (thrombolysis and beta-blockers) and the patency of the infarct related vessel. Patients with an infarct had diminished vagal tone as compared with the control group. Those patients with occluded related arteries showed higher incidence of late potentials; interestingly patients with late potentials also had diminished vagal tone. Without looking at the patency of the infarct related artery, thrombolitic and betablocker therapy did not have any effect on vagal tone. All the variables were correlated with the patency of the infarct related artery. Those patients with patent arteries had a preservation of the vagal tone; this was independent of the treatment received and the presence of late potentials. We concluded that the patency of the infarct related artery determines the absence of late potentials and preservation of the vagal tone. This might be one of the mechanisms of how thrombolitic therapy decreases the incidence of cardiac death.

[Orthostatic intolerance syndromes]. / Los síndromes de intolerancia ortostática.

In patients with an orthostatic intolerance, the hemodynamic response to standing, may identify an abnormality know as postural orthostatic tachycardia syndrome or orthostatic hypotension, that can often be treated without further testing. When the response to standing is normal, tilt-table testing may be useful in making the diagnosis of vasovagal syncope or postural orthostatic tachycardia syndrome and guiding treatment. In evaluating the results of tilt-table testing, an important consideration is the distinction between vasovagal syncope, and the dysautonomic response to tilt characterized by a gradual and progressive decrease in blood pressure that leads to syncope. Current practice patterns suggest that beta blockers, fludrocortisone, and midodrine are commonly used to treat patients with vasovagal syncope. These also suggest that patients with the postural orthostatic tachycardia syndrome, and with the dysautonomic response, are better treated with fludrocortisone and midodrine.

[Electrocardiographic changes during stress test in a patient with "Brugada syndrome"]. / Alteraciones electrocardiográficas durante el esfuerzo en un paciente con "síndrome de Brugada".

We report a 28 year old man with the Brugada syndrome characterised by an electrocardiographic pattern of a right bundle branch block and an ST segment elevation in the right precordial leads as well as syncope. During an exercise test, we observed a normalization of the ST segment in V2+ while in the postexercise phase, the ST segment elevation in the right leads was established. This is the first case reported of the Brugada syndrome in Mexico, with spontaneous changes on the EKG masked during exercise and apparent during postexercise phase.

[Usefulness of adenosine to detect advanced paroxysmal atrioventricular block as a cause of syncope]. / Utilidad de la adenosina para evidenciar bloqueo auriculoventricular avanzado paroxístico como causa de síncope.

We present the case of a 66 years old man with recurrent episodes of syncope, up to three times during the last two months without previous symptoms. An ECG after the syncope showed a bilateral block (left anterior fascicle block and right bundle branch block) and first grade atrioventricular block. The exercise test did not demonstrate either AV conduction disorders or tachyarrhythmia episodes. Holter monitoring showed premature ventricular complexes; tilt testing and carotid sinus massage were normal. The electrophysiologic study revealed no alteration in the conduction system. Throughout atrial and ventricular stimulation documented no tachyarrhythmias. However, intravenous administration of 12 mg of adenosine induced complete AV infra-His block with ventricular asystolia of 7.2 sec duration. Adenosine testing can identify patients with syncope due to paroxysmal AV block even when the electrophysiological findings and other conventional tests are not conclusive.

[Radiofrequency ablation in the treatment of tachyarrhythmias. Experience concerning 1,000 consecutive patients]. / Ablación con radiofrecuencia en el tratamiento de las taquiarritmias. Experiencia en 1000 pacientes consecutivos.

Several reports have demonstrated that radiofrequency catheter ablation provides effective control of a variety of tachyarrhythmias. This report details the results of radiofrequency catheter ablation in 1,000 consecutive patients with a wide variety of tachyarrhythmias treated in the Instituto Nacional de Cardiología "Ignacio Chavez". Tachyarrhythmias were associated with the presence of an accessory pathway in 700 patients (70%). Dual accessory pathways were present in 21 patients, giving a total of 722 accessory pathways. The mechanism of the arrhythmia was AV nodal reentrant tachycardia in 204 patients (20.4%). Ablation of the reentrant circuit of atrial flutter within the right atrium was attempted in 56 (5.6%) patients and a primary atrial tachycardia in five patients (0.5%). AV node ablation and permanent pacemaker implantation were performed in 17 patients (1.7%). Finally we performed radiofrequency catheter ablation in 22 (2.2%) patients with ventricular tachycardia. Radiofrequency catheter ablation was successful in 630 of 700 (90%) patients with accessory pathways with a complication rate of 9/700 (1.2%) and a recurrence rate of 73 (12.4%). AV nodal reentry was successfully abolished in 190 of 204 (93%) patients by selective ablation of the slow pathway in 168/180 (93.3%) patients and the fast pathway in 22/24 (92%) patients. The complication rate of this group was 7/204 (3.4%) with a recurrence rate of 30 patients (14.2%). The reentrant circuit of atrial flutter was ablated successfully in 41 of 56 (73%). Four/five (80%) of patients with primary atrial tachycardia were successfully ablated. Complete AV block was achieved in 17/17 patients with atrial fibrillation or flutter treated by AV nodal ablation without complications or recurrence. The procedure was successful in 17/22 (77%) of patients with ventricular tachycardia. The results of this series of patients demonstrate the safety and efficacy of radiofrequency ablation for the treatment of a wide variety of tachyarrhythmias with high rate of success 899/1,000 (89.9%) and with an 1 1.8% of recurrence, low risk of complications (1.5%) and no mortality.

[Diltiazem in chronic stable angina]. / Utilidad del diltiazem en la angina de esfuerzo crónica estable.

The safety and efficiency of the administration of diltiazem was evaluated in 10 patients with class II-III chronic stable angina. All the patients had ischemic heart disease documented by coronary angiography and/or an abnormal exercise test. A dose related improvement in both frequency of angina and exercise capacity were obtained by diltiazem administered in increased doses using a single blind protocol. The weekly frequency of angina was reduced from 7.5 +/- 9.8 with placebo to 3.8 +/- 5.5, 1.1 +/- (p less than 0.05) and 0.7 +/- 0.9 (p less than 0.01) with doses of 120, 240 and 360 mg/day respectively. The exercise duration on treadmill was significantly increased from 8.5 +/- 3.6 to 10.6 +/- 3.7 min (p less than 0.05) with the 360 mg/day dose. The mean exercise time required to develop 1 mm ST depression was 6.1 +/- 3 min on placebo and was significantly delayed to 9.0 +/- 3.8 min (p less than 0.05) with the 240 mg/day dose and to 10.7 +/- 4.0 min with 360 mg (p less than 0.01). In a double blind randomized crossover phase, the time to the onset of ischemia during exercise was increased from 8.5 +/- 3.8 min with placebo to 11.05 +/- 2.8 min with 360 mg/day of diltiazem (p less than 0.01). Diltiazem in doses ranging from 120 to 360 mg/day is an effective antianginal agent with no significant adverse effects.

[Acute nonspecific pericarditis]. / Pericarditis aguda inespecífica.

In order to learn the natural history of nonspecific acute pericarditis in our environment, we studied retrospectively 50 patients seen at The Instituto Nacional de Cardiología Ignacio Chávez, between 1972-1985. The clinical history, electrocardiogram, chest x ray, laboratory findings, as well as the outpatient follow-up were analyzed. There was a history of a respiratory or gastrointestinal infection, probably viral in origin, in almost half of the cases (46%). Chest pain was present in 96% of the patients and was the most common symptom. In only half of the patients a pericardial friction rub was heard. A typical S-T elevation was found in 90% of the electrocardiograms. Arrhythmias and conduction disorders were unusual. The echocardiogram showed a pericardial effusion in seven patients and six had a pleural effusion. Only one patient developed signs of cardiac tamponade. None of the patients in this study developed a chronic constrictive pericarditis and there were no deaths. Before or after hospitalization, 14 patients (28%) had multiple episodes of chest pain suggestive of recurrent pericarditis. This study shows that nonspecific acute pericarditis seems to be a self-limited illness with a good prognosis, few recurrences and practically no complications.

[Vector cardiographic evaluation of monomorphic ventricular tachycardia; its relation to the type of cardiopathy, vagal tonus and the prevalence of late potentials]. / Evaluación vecto-espacial de la taquicardia ventricular monomórfica; relación con el tipo de cardiopatía, tono vagal y prevalencia de potenciales tardíos.

The most common cause of sudden death is malignant ventricular arrhytHmia. In order to identify the predictive value of the vectospatial evaluation in the surface electrocardiogram during a monomorphic ventricular tachycardia (MVT), and the equilibrium state of AutonomOus Nervous System (ANS), 89 patients of both sexes were studied with mean age of 47 +/- 16.2 years. They were grouped as follows: Group I included 43 patients (P), with a coronary heart disease; Group II (n = 24P) with a noncoronary myocardiopathy and Group III (n = 22P) with unknown origin MVT (Cryptogenic). Relationship between QRS configuration in the frontal plane (QRSf) during MVT episode with transverse plane, cardiac position in the chest X-rays, presence and duration of late potentials (LPs) in their two types of analysis (time domain and spectral mapping by high-resolution electrocardiogram), heart rate variability and ejection fraction by echocardiography were determined in all patients. The QRSf configuration with left bundle-branch block (LBBB) was the most common in group I, the sustained MVT (SMVT) + LBBB was associated with both prevalence and duration of late potentials (p = 0.005), low-rate heart variability and ejection fraction < 40%. SMVT + LBBB was the most common type in group III and if it has shown and inferior axis, an elevated rate of LPs (+) was seen. Situation that oriented to an arrhythmogenic right ventricular dysplasia. Low amplitude signals with short duration in the time domain were seen in group I with LBBB; and with SMVT + RBBB in group II. We suggest that vectospatial evaluation of QRSf during a MVT is a greater importance in the risk stratification for sudden death and it can guide to anatomic origin and the diagnosis-therapeutic approach.

[Late potentials and variability of cardiac frequency in chronic chagasic myocardiopathy and other myocardiopathies]. / Potenciales tardíos y variabilidad de la frecuencia cardiaca en la miocardiopatía chagásica crónica y otras miocardiopatías.

In patients suffering dilated cardiomyopathy, chagasic or not, and in healthy volunteers we applied signal-averaged electrocardiography to detect late potentials and to study heart autonomic control. Thus, with non-invasive methods, we were able to explore the progress of depolarization and heart rate variability. It was found that Chagasic patients have more late potentials and abnormalities in the heart variability; with less co-morbid process when compared with patients suffering miscellaneous cardiomyopathies. These preliminary findings corroborate and expand previous observations by several authors. The signal-averaged electrocardiogram is a valuable tool for clinical diagnosis and research, particularly for studies on dilated cardiomyopathy, specially those with parasitic etiology.

[Usefulness of the pre-excitation index to determine the mechanism of supraventricular paroxysmal tachycardia and the location of the anomalous pathway]. / Utilidad del índice de preexcitación para determinar el mecanismo de la taquicardia paroxística supraventricular y la localización de la vía anómala.

To evaluate the preexcitation index in determinate the mechanism of paroxysmal supraventricular tachycardia and localize accessory pathway, fifty nine patients with clinical and electrocardiographic supraventricular tachycardia were analyzed. There were thirty eight patients (64.4%) with orthodromic AV reentry using an accessory pathway for retrograde conduction and 21 patients (35.6%) with typical AV nodal reentrant tachycardia. Preexcitation of the atrium during tachycardia by premature ventricular complex at a time when anterograde His bundle activation was present in 30 o 38 (79%) patients with AV reentry while only 8 of 21 (38%) patients with AV nodal reentry demonstrated preexcitation during tachycardia. There was no significant difference between left and right accessory pathways and in mean tachycardia cycle length between the two groups. However, atrioventricular reentry demonstrated atrial preexcitation during tachycardia more frequently than AV nodal reentry. In conclusion, our findings show that the preexcitation index is a useful method for determinate the mechanism of supraventricular tachycardia and to localize accessory pathways.

[Infusion of fluids into the pulmonary artery in the treatment of acute myocardial infarction extending to the right ventricle. Evaluation of the method]. / La infusión de líquidos en la arteria pulmonar en el tratamiento del infarto agudo del miocardio extendido al ventrículo derecho-Valoración del método.

Seventeen patients with diagnosis of acute myocardial infarction with right ventricular extension were studied. All of them had evidence of contractile impairment of the right ventricle as shown by elevated filling pressure of the right ventricle, low systolic pulmonary pressure and low left ventricular filling pressure and cardiac output. These patients were treated with fluid infusion into the pulmonary artery besides other treatment measures for myocardial infarction in order to improve the filling pressure of the left ventricle and the cardiac output without stressing the right ventricle. The results obtained with this approach, which was maintained for 22 hours, showed a significant improvement in the stroke work indices of both ventricles and also in the cardiac output with a decrease in peripheral resistence without ever loading the ventricles. We analyze the physiological basis for using this procedure and also the complications that can occur. Our results show that the infusion of fluid into the pulmonary artery improves the hemodynamic situation of these patients and protects a damaged right ventricle.

[Rational management of arrhythmias]. / Un enfoque racional del manejo de las arritmias.

Despite the development of better diagnostic techniques and new modes of therapy, management of cardiac arrhythmias is still difficult. The lack of standardization in the indications of each technique has increased the risk of overtreatment and unnecessary cost. This paper describes the minimal requirements necessary for the different techniques and the appropriate information that should be collected from each. A well taken clinical history and a 12-lead EKG give very important information for the decision on when and how to treat.

[The termination of auricular flutter by noninvasive programmed electrical stimulation using a permanent AAI-mode pacemaker]. / Terminación de un flutter auricular por estimulación eléctrica programada no invasiva utilizando un marcapaso permanente en modalidad AAI.

We describe a case of a 15-year-old boy with an atrial septal defect who three years after the direct closure of the defect presented with atrial flutter type I according to Wells's classification. He was then electrically cardioverted but presented immediately sinus bradycardia and a ventricular escape rhythm that required epicardial pacing (Intermedics 292-03 DASH) in the AAI mode. We report here the successful termination of a new episode of atrial flutter into sinus rhythm with a noninvasive programmed stimulation using his previously implanted pacing system.

[Exercise test in patients with permanent pacemakers]. / La prueba de esfuerzo en pacientes con marcapaso permanente.

From June 1988 to June 1990 we studied fifty patients who had implantation of a pacemaker. (31 females and 19 males). All of them underwent stress test with Bruce's protocol. Patients were divided in two groups; pacemaker-independent (PI) and pacemaker-dependent (PD). Over 50% of the patients inhibited the pacemaker with their own rhythm, most of them had sinus dysfunction. Complete A-V block was predominant in PD. The group of PI achieved more mets and had more oxygen consumption. Blood pressure response was similar in both groups.

[The electrocardiographic changes in patients stung by scorpions]. / Alteraciones electrocardiográficas en sujetos picados por alacrán.

Scorpion sting is a hazardous and potentially lethal condition. Venom of some variety of scorpion can cause dramatic cardiovascular and electrocardiographic changes, that have been related to heart stimulation by autonomous nervous system. We prospectively studied 722 patients following scorpion sting. Mean age for the group was 25.5 +/- 18.3 years. 67% were less than 30 years of age. In 294 patients (40.7%) we found electrocardiographic changes. These cases were followed until those changes disappeared. First degree atrioventricular block was found in 10.2%. Intraventricular conduction disturbances in 12.8% with predominance of right bundle branch block. In 11% we found arrhythmias. In 15% reversible ventricular repolarization changes. Of this no one died. This lack of mortality could be attributed to a prompt therapeutic intervention.

[Rupture of the free wall of the heart as cause of death in acute myocardial infarct]. / Ruptura de la pared libre del corazón como causa de muerte en el infarto agudo del miocardio.

Twenty four cases with myocardial rupture among 259 patients with autopsy after death due to myocardial infarction, were compared with patients with acute myocardial infarction and death secondary to other causes. Myocardial rupture occured during the first 72 hours in 58% of the patients and all cases within the first five days. Two thirds of the patients were males and 46% were 70 years of age. There were 24 myocardial ruptures (9.5%). Previous history of arterial hypertension and un-remittent anginal pain were predisposing factors for rupture (p=0.05). Other previously reported bad prognostic factors such as persistent hipertension after acute infarction, severe exercise before infarction and history of Diabetes Mellitus were not statistically significant in this study. Ruptured myocardium was not influenced by a previous history of myocardial infarction, hospitalization delay in the C.C.U., administration of anticoagulants, digitalis or pressor amines. There was no significant difference among the groups compared in enzyme curves or magnitude of leucocytosis. Electromechanic dissociation, sinus bradycardia, nodal rhythm followed by idioventricular rhythm and asystole, were observed following myocardial rupture.

[Effect of hypoxia on atrio-ventricular conduction in severe respiratory insufficiency]. / El efecto de la hipoxia sobre la conducción auriculoventricular en la insuficiencia respiratoria grave.

The role of hipoxia on A-V conduction was studied in the patients with severe respiratory insufficiency. Intervals of A-V conduction were measured under basal conditions, breathing room air and with increasing atrial rates. Results are compared with those obtained after the administration of 99% oxygen. A-V conduction times were normal in all the patients while breathing room air and in response to atrial pacing. With oxygen administration most patients had a decrease in A-V conduction at the expense of a prolonged A-H time, without significant alteration of the other time intervals. A-V conduction in chronic hipoxia with a PaO2 above 28 mm Hg is not delayed. Intranodal conduction delay with oxygen administration may be due to a decrease in sympathetic nerve stimulation.

[Radiofrequency ablation in tachycardias due to accessory pathways in a pediatric population]. / Ablación con radiofrecuencia en taquicardias por vías accesorias en una población pediátrica.

Catheter ablation of accessory atrioventricular pathways using radiofrequency current was attempted in 61 children and young adolescents less than 18 years of age who were referred for treatment of symptomatic supraventricular tachycardia. Thirty-three children had the Wolff-Parkinson-White syndrome and 30 tachyarrhythmias related to an accessory pathway conducting only in retrograde fashion. Ablation of left sided accessory pathways was usually attempted utilizing an arterial approach to the annulus of the mitral valve, only in one case we used the transseptal approach, while the venous route to the atrial aspect of the tricuspid valvular annulus was chosen for right sided accessory connections. Ablation of 55 of 63 accessory connections was achieved (87% success) with a range of 1 to 42 applications of radiofrequency current. The sessions were completed within 19 to 180 minutes, and we used within 16 to 45 watts of radiofrequency current. Two patients had complications as a result of their ablation procedure. One patient had complete heart block but did not require pacemaker implantation, and other one had mitral regurgitation. A second session was necessary in three patients, two of three accessory pathways were ablated, giving a success rate of 90%. During a one year period of follow-up, we had 4 recurrences (7.2%). Catheter ablation using radiofrequency current is a highly effective and safe curative approach for treating young patients with supraventricular tachycardia mediated by accessory pathways.

[Identification of patients at risk of malignant arrhythmia in the 1st year after myocardial infarction]. / Identificación de los pacientes con riesgo de arritmias malignas en el primer año postinfarto del miocardio.

Two hundred twenty two consecutive patients with acute myocardial infarction were followed for one year. We evaluated the usefulness of late potentials, the spectral analysis, heart rate variability, infarct-related coronary artery, ejection fraction, arrhythmias during Holter monitoring and other clinical variables as risk markers for developing of ventricular arrhythmias and/or sudden death. Twenty four patients (10.8%) had late arrhythmic events: sudden death in 7, sustained ventricular tachycardia in 15 and unexplained syncope in 2. Late potentials had high sensitivity (94%) and negative predictive value (99%), followed by an occluded related-infarct coronary artery (75% sensitivity and 96% negative predictive value). Complex ventricular arrhythmias during Holter monitoring was the test with the highest specificity (92%). A combination of late potentials plus an occluded infarct-related coronary artery or late potentials plus ejection fraction showed 100% sensitivity with 100% negative predictive value. Of the 16 studied variables, 5 had independent and significative value as a predictor of arrhythmic events, these are, according to the relative risk: late potentials (20.2), ejection fraction less than 40% (12.1), complex arrhythmias during Holter monitoring (7.5), the presence of an occluded infarct-related coronary artery (6.4) and anterior myocardial infarction localization (4.5). We consider, that with a combination of simple methods of assessment, we can select a subgroup of survivors of an acute myocardial infarction at high risk of developing ventricular arrhythmias and sudden death, which also identifies patients with low risk for these complications.