Electrophysiological Studies on Cardiac Catheter Ablation

Clinical and animal investigations have pointed out that high energy electrical shocks are associated with the development of cardiac arrhythmias and with variable success in permanent ablation. The effects of electrode configuration and location on the size of the recorded electrogram was investigated to help explain variable catheter ablation results. We analyzed the cellular effects of catheter ablation shocks and found depression of resting potential, action potential amplitude, dV/dt and action potential duration. The most severe effects were noted with high current densities in tissues located between the cathode and anode. Damage was worse nearest the cathode. Similar cellular studies were completed using argon laser photoablation. Again, there was a decrease in resting potential, action potential amplitude and dV/dt. Laser energy led to a more focal region of myocardium void of action potentials and the border zone of injury was smaller. We also investigated the effects of lower energy shocks)1 to 10 joule) on cardiac tissues. Using microelectrodes, we observed that the membrane potential can "hang up" at the depolarized levels for varying periods of time and that conduction is altered during this membrane "hang-up" period. The duration and membrane hang-up level correlated with shock intensity and shock duration. Sequential shocks resulted in additive membrane "hang-up". We believe that membrane hang-up may be associated with brief arrhythmias observed following catheter ablation since conduction, refractoriness and excitability are all altered.     

Diesel Exhaust Is a Pulmonary Carcinogen in Rats Exposed Chronically by Inhalation

Diesel Exhaust Is a Pulmonary Carcinogen in Rats Exposed Chronicallyby Inhalation. MAUDERLY, J. L., JONES, R. K., GRIFFITH, W. C.,HENDERSON, R. F., AND MCCLELLAN, R. O. (1987). Fundam. Appl.Toxicol 9, 208–221. Male and female F344 rats were exposed7 hr/day, 5 day/week for up to 30 months to automotive dieselengine exhaust at soot concentrations of 0.35, 3.5, or 7.0 mg/m³or were sham-exposed to clean air. Rats were terminated at 6-monthintervals to measure lung burdens of diesel soot and for histopathology.Other rats either died or were terminated after 30 months ofexposure. Lungs were fixed, sectioned into 3-mm slices, andexamined by a dissecting microscope to detect tumors. Lesionswere stained and examined by light microscopy. Survival andbody weight were unaffected by exposure. Focal fibrotic andproliferative lung disease accompanied a progressive accumulationof soot in the lung. The prevalence of lung tumors was significantlyincreased at the high (13%) and medium (4%) dose levels abovethe control prevalence (1%). Four tumor types, all of epithelialorigin, were observed: adenoma. adenocarcinoma, squamous cyst,and squamous cell carcinoma. Logistic regression modeling demonstrateda significant relationship between tumor prevalence and bothexposure concentration and soot lung burden. These results demonstratethat diesel exhaust, inhaled chronically at a high concentration,is a pulmonary carcinogen in the rat.     

Interpolating Unipolar Epicardial Potentials from Electrodes Separated by Increasing Distances

In cardiac mapping, potentials for unexplored areas are estimated by interpolating values from nearest neighbor electrodes regardless of distances between these sites or wave front orientation. The effects of these variables on interpolated unipolar electrograms were analyzed two ways: with a computer model and with electrograms recorded 9.9 and 14.1 mm apart. For the model, wave fronts (n = 39) were generated from electrograms recorded during right ventricular (RV) activation in five dogs following the RV isolation procedure. Each wave front was assumed to propagate radially at 0.5 m/sec from a site 30 mm from the center of a square array with electrodes located at the center and corners. Each wave front crossed the array with its tangent at an angle of 0 degrees, 45 degrees, or 90 degrees to the diagonal line connecting opposite corner electrodes. Potentials for all five sites were generated from each wave front and were interpolated for the center site from the generated corner potentials. Generated and interpolated center site potentials were compared using correlation coefficients (r) and percent root mean square differences (%RMSD). Mean r values fell below 0.90 for interelectrode distances of 15.6 mm, 2.8 mm, and 1.4 mm at 0 degrees, 45 degrees, and 90 degrees wave front orientations, respectively. For experimentally measured potentials recorded 9.9 mm apart, results from interpolated electrograms were similar to results from the model at 0 degrees propagation. Electrograms interpolated from potentials measured 14.1 mm apart had poorer r and %RMS values than those from the computer model. Thus, with linear interpolation unipolar electrograms can be inaccurately interpolated from electrodes less than 3 mm apart or correctly interpolated from electrodes more than 14 mm apart depending upon wave front orientation.     

Permanent Cardiac Pacing After Open Heart Surgery: Congenital Heart Disease

A retrospective review of 6,004 patients who underwent open repair of congenital heart defects revealed that 132 patients (2.2%) required permanent cardiac pacing postoperatively. The indications for pacing were early atrioventricular (AV) block in 55%, late onset AV block in 31%, and sick sinus syndrome in 14%. A ventricular septal defect (VSD) was the most common congenital anomaly present alone or in association with other lesions in 67% of the patients. Atrial surgery accounted for 21% of the patients requiring pacing. Ten-year patient survival was found to be 66% (+/- 6%). Thirty-five percent of the deaths were sudden and unexpected, presumably due to an arrhythmia. Reoperation for pacing system failure has occurred too frequently (12% per year). The most common causes for reoperation were battery failure (44%) and exit block (25%).     

Long-Term Threshold Stability with Porous Tip Electrodes

Experience with 163 unipolar tined porous endocardial electrodes is reported. One patient required repositioning of the electrode because of exit block. There were no other complications in the entire series of patients. All of the patients had low chronic stimulation thresholds. The mean pulse width 24 hours after implantation was 0.0534 ± 0.0128 ms. Seventy-four patients were restudied six months after implantation. The mean pulse width threshold was then 0.07432 ± 0.0775 ms. Fifty-four patients were evaluated one year after lead implantation. The mean pulse width threshold was then 0.0611 ± 0.0230 ms. The pulse generator was reprogrammed to a lower pulse width in all of the patients. This permitted a substantial prolongation of the pulse generator life. The cost effectiveness of the pulse generator was also greatly improved by pacing with reduced pulse widths. In an additional 16 patients, the voltage amplitude was reduced from 5.0 volts to 2.5 volts. This permitted an even greater increase in the pulse generator longevity.     

Diaphragm Pacing with a Quadripolar Phrenic Nerve Electrode: An International Study

We sought to determine the international experience with the quadripolar diaphragm pacer system and to test two hypotheses: the incidence of pacer complications would be (1) increased among pediatric as compared to adult patients; and (2) highest among active pediatric patients with idiopathic congenital central hypoventilation syndrome (CCHS). Data were collected via a questionnaire coupled with the Atrotech Registry data for a total of 64 patients (35 children and 29 adults) from 14 countries. Thoracic implantation of electrodes and bilateral pacer use each occurred in 94% of all subjects. Tetraplegic (vs pediatric CCHS) patients were more typically paced 24 hours/day (P = 0.001). Pacing duration averaged 2.0 ± 1.0 years among children and 2.2 ± 1.1 years among adults. Infections occurred among 2.9% of surgical procedures, all in pediatric CCHS patients (vs pediatric tetraplegic patients, P = 0.01). The incidence of mechanical trauma was 3.8%, without significant differences among patient groups. The incidence of presumed electrode and receiver failure were 3.1% and 5.9%, respectively, with internal component failure greater among pediatric CCHS than pediatric tetraplegic patients (P < 0.01). Intermittent or absent function of 0–4 electrode combinations occurred among 19% of all patients, with increased frequency among pediatric CCHS than pediatric tetraplegic patients (P < 0.03). Complication- free successful pacing occurred in 60% of pediatric and 52% of adult patients. In all, 94 % of the pediatric and 86% of the adult patients paced successfully after the necessary intervention. Although pacer complications were not increased among pediatric as compared to adult patients, the incidence of complications was highest among the active pediatric patients with CCHS. Longitudinal study of these patients will provide invaluable information for modification and improvement of the quadripolar system.     

CONSTRUCTION OF A MODEL FOR COMPUTER-ASSISTED DIAGNOSIS: APPLICATION TO THE PROBLEM OF NON-TOXIC GOITRE

This study describes the construction of a model for the computer-assisteddiagnoses of non-toxic goitre. From a study of 53 patients with Hashimoto's disease, 51 withsimple goitre and 51 with thyroid cancer, information was obtainedwhich was used in the construction of a probability matrix.The diagnosis was confirmed histologically in all of these patients. The probability matrix was constructed from 30 pieces of informationrelating to the results of history taking, clinical examination,and laboratory investigations and consisted of a table of theobserved incidence of each piece of information in each of thethree diseases. This probability matrix was then fed into anElliott 803 automatic digital computer and formed the memoryof the computer for these three diseases. A fresh series of 88 patients, 43 with Hashimoto's disease,26 with simple goitre, and 19 with thyroid cancer were thenstudied. Clinical information and the results of laboratorystudies were provided as data to the computer to calculate adiagnosis for these patients. Two slightly different applications of probability theory wereused for each calculation. In one (Bayesian probability) theratio of the prior probabilities that any patient would haveHashimoto's disease, simple goitre, or thyroid cancer beforeany tests or observations had been made, were taken to be 10:89and 1 respectively on the basis of observations previously madeon a population of patients attending a thyroid clinic. In theother application of probability theory (relative likelihood)the prior probabilities of occurrence of the three diseaseswere assumed to be equal. The diagnoses given by both methods were compared with eachother and with the diagnosis of a clinician experienced in dealingwith thyroid disorders. In all patients in whom discordenceof opinion occurred a histological diagnosis was accepted asthe final diagnosis. The method using relative likelihood was considered to be superiorto the method using Bayesian probability for in no patient didrelative likelihood miss a diagnosis of thyroid cancer whenthe clinician diagnosed thyroid cancer. This was not true forBayesian probability which missed three cases of clinicallyobvious cancer. The possible reasons for this superiority ofrelative likelihood are discussed in the paper. The results given by relative likelihood agreed with the clinician'scorrect diagnosis of Hashimoto's disease in 26 of 28 patients.The calculated diagnosis was wrong in two of these patientsin whom the clinician made the correct diagnosis. In another12 patients in whom the clinician made a wrong diagnosis, thecalculations based on relative likelihood gave the correct diagnosis.In a further three patients the clinical and calculated diagnoseswere both wrong. In 24 of the 26 patients with simple goitre the clinician madethe correct diagnosis. In 21 of these patients the diagnosiscalculated by relative likelihood was correct and in three patientsit was wrong. In two patients both the calculated and clinicaldiagnoses were wrong. Of the 19 patients with thyroid cancer 16 were correctly diagnosedby relative likelihood and by clinician alike. The remainingthree patients in this group were incorrectly diagnosed by both. It is concluded that the results of this study support the contentionthat a correct diagnosis can be calculated using the theoryof conditional probability. Many difficulties remain to be overcomein what still remains a highly experimental approach to theproblem of diagnosis. ²Present address, Medical Research Council, Computer ServicesCentre, 171-4 Tottenham Court Road, London, W.1. ³Western Infirmary, Glasgow, W.1.     

T Wave Complexity in Patients with Hypertrophic Cardiomyopathy

The complexity of the T wave assessed by principal component analysis (PCA) has been proposed to reflect obnormal repolarization, which may be arrhythmogenic. To determine whether PCA can differentiate patients with hypertrophic cardiomyopathy (HCM) from normal subfects and whether PCA is of prognostic importance in HCM, 112 patients with HCM (41 ±14 years, 64 males) and 72 healthy subjects (39 ± 9 years, 41 males) were studied. Patients with sinus node dysfunction, AV conduction block, flat T waves, QRS > 140 ms, and those < 15 years were excluded from this study. Standard 12-lead ECGs were recorded digitally using the MAC-VU system (Marquette Medical Systems). PCA parameters were computed using the QT Guard software package by Marquette. PCA ratio was significantly greater in HCM patients than in normal controls (23.9%± 12.4% vs 16.1%± 7.6%, P < 0.0001) and was correlated with QT-end dispersion (r = 0.24. P = 0.01) and QT peak (Q point to T peak) dispersion (r = 0.35, P < 0.0001). HCM patients with syncope (n = 23) had increased PCA ratios compared with those without syncope (29.1%± 11.5% vs 22.5%± 12.3%, P = 0.01). PCA ratio was similar in patients with and without nonsustained ventricular tachycardia on Holter (25.9%± 11.4% vs 22.7%± 12.1%, P = 0.2), as well as in patients treated with amiodarone or sotalol versus those not on therapy. In conclusion, assessment of the complexity of the T wave by PCA differentiates HCM patients from normal subjects. PCA ratio correlated with QT dispersion and an increased PCA ratio was associated with a history of syncope in HCM.     

Diastolic Potentials Recorded by Surface Electrocardiographic Signal Averaging During Sustained Ventricular Tachycardia: Possible Origin From the Reentrant Circuit

ECG signal averaging can detect low amplitude diastolic potentials in sinus rhythm. We, therefore, recorded signal-averaged ECGs during eight episodes of inducible uniform sustained VT with coincident atrial pacing to look for continuous diastolic electrical activity. Simultaneous AV pacing in seven patients served as controls. The number of QRS complexes averaged (187 +/- 47 vs 183 +/- 63), the noise level (1.26 +/- 0.88 vs 1.39 +/- 0.47) and cycle length (385 +/- 52 vs 404 +/- 40) did not differ between VT and paced recordings. In each lead the difference in onset between the unfiltered surface recording and the filtered data (40 Hz bidirectional) was significantly greater in VT than the paced recordings (25 +/- 16 vs 11 +/- 8 msec, P = 0.0012). These late diastolic (pre-QRS) potentials were greater than 15 msec duration in 65% of the leads in VT versus 20% of paced recording (P = 0.021). The maximum value was greater than 20 msec in six VT (75%) versus one (14%) paced recording (P = 0.019). The earliest filtered onset in any lead preceeded the earliest surface activity by greater than 12 msec, in 6 VT versus one paced recording (P = 0.019). Early diastolic (post-QRS) potentials were also longer in VT than pacing (49 +/- 40 versus 5 +/- 20, P = 0.001) and exceeded 38 msec in seven of the VTs but none of the paced recordings (P = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)