Double external direct-current shocks for refractory atrial fibrillation.

Encouraged by preliminary data using double external direct-current (DC) shocks in patients with atrial fibrillation refractory to single external DC shocks, we undertook a prospective study of all patients with atrial fibrillation of > 1-month duration using a shock sequence with (1) 1 shock of 200 J anterior-posterior, (2) 1 shock of 360 J anterior-posterior, (3) 1 shock of 360 J apex-anterior, and (4) double shocks with configurations 2 and 3 delivered almost simultaneously by 2 defibrillators. The double shocks appeared to be safe and restored sinus rhythm in approximately 2 of 3 of patients in whom DC cardioversion failed with single shocks.

Randomized, double-blind comparison of intravenous amiodarone and bretylium in the treatment of patients with recurrent, hemodynamically destabilizing ventricular tachycardia or fibrillation. The Intravenous Amiodarone Multicenter Investigators Group.

BACKGROUND: After several days of loading, oral amiodarone, a class III antiarrhythmic, is highly effective in controlling ventricular tachyarrhythmias; however, the delay in onset of activity is not acceptable in patients with immediately life-threatening arrhythmias. Therefore, an intravenous form of therapy is advantageous. This study was designed to compare the safety and efficacy of a high and a low dose of intravenous amiodarone with bretylium, the only approved class III antiarrhythmic agent. METHODS AND RESULTS: A total of 302 patients with refractory, hemodynamically destabilizing ventricular tachycardia or ventricular fibrillation were enrolled in this double-blind trial at 82 medical centers in the United States. They were randomly assigned to therapy with intravenous bretylium (4.7 g) or intravenous amiodarone administered in a high dose (1.8 g) or a low dose (0.2 g). The primary analysis, arrhythmia event rate during the first 48 hours of therapy, showed comparable efficacy between the bretylium group and the high-dose (1000 mg/24 h) amiodarone group that was greater than that of the low-dose (125 mg/24 h) amiodarone group. Similar results were obtained in the secondary analyses of time to first event and the proportion of patients requiring supplemental infusions. Overall mortality in the 48-hour double-blind period was 13.6% and was not significantly different among the three treatment groups. Significantly more patients treated with bretylium had hypotension compared with the two amiodarone groups. More patients remained on the 1000-mg amiodarone regimen than on the other regimens. CONCLUSIONS: Bretylium and amiodarone appear to have comparable efficacies for the treatment of highly malignant ventricular arrhythmias. Bretylium use, however, may be limited by a high incidence of hypotension.

Unusual Wenckebach upper rate response of an atrial-based DDD pacemaker.

We describe in this report an unusual form of Wenckebach upper rate response produced by a DDD pulse generator with atrial-based lower rate timing. The pacemaker maintained the programmed upper and lower rate intervals at the expense of a prolonged atrial paced-ventricular paced AV interval. This form of upper rate behavior eliminated the longer cycle (containing the unsensed P wave) that occurs at the end of the pacemaker Wenckebach sequence during traditional DDD pacing with ventricular-based lower rate timing.

Pacemaker hemodynamics: clinical implications.

Our review of the current literature and experience in caring for pacemaker patients suggests that a consideration of hemodynamics is a logical way to approach pacemaker selection and programming. Multiple clinical factors enter into the selection of a pacemaker or pacemaker programming settings in each case. It appears that in patients with sinus node disease, atrial-inhibited or dual-chamber pacing provides the best chance for preventing the development of chronic atrial fibrillation with its attendant risks of embolism and stroke. It is clear that AV synchrony has beneficial hemodynamic effects at rest in most patients. The results of Labovitz would suggest that in patients with marked left atrial enlargement, this may be less so. The results of Stewart et al would further suggest that in patients with retrograde VA conduction, dual-chamber pacing is preferable. Retrograde VA conduction can be intermittent and this makes it difficult to use its absence on a single test to decide on the type of pacemaker to use. It appears that baseline left ventricular function does not determine the relative improvement in cardiac output observed with AV synchrony or rate-adaptive pacing. However, in patients with severe congestive heart failure even a small improvement in cardiac output may result in significant clinical improvement. Studies have shown that in any given patient, there may be an optimal AV interval at rest. In general, this ranges from 100 to 150 milliseconds. In normal individuals the optimal AV interval shortens with increased heart rate during exercise in a predictable and linear fashion. The hemodynamic benefits of a shortened AV interval with faster heart rates in pacemaker patients have not yet been shown. Intuitively, however, this would appear to be a desirable approach and will probably be added to the design of future generations of dual-chamber pacemakers. Studies of the effect of different pacing modes on secretion of atrial natriuretic factor are intriguing and may contribute more to our understanding of pacing hemodynamics in the future. During exercise, heart rate increase is more important than AV synchrony and this has been shown by several studies. Thus, in active patients with chronotropic incompetence due to sick sinus syndrome, the addition of rate-adaptive pacing is important. Because single-chamber rate-adaptive atrial pacing leaves the patient exposed to the risk of future development of AV block and DDD pacing does not provide chronotropic support, it is likely that the new rate-adaptive dual-chamber (DDDR) devices will be used in a significant number of these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic and antiarrhythmic effects of magnesium in patients with inducible ventricular tachyarrhythmia.

Intravenous magnesium is reported to be effective in the treatment of ventricular arrhythmias associated with hypomagnesemia, digitalis toxicity, or prolongation of the QT interval. In most previous reports, magnesium was added to conventional antiarrhythmic drugs that had failed. There are few data on the antiarrhythmic efficacy of magnesium as monotherapy in patients without these associated abnormalities. Ten patients with life-threatening ventricular arrhythmia and inducible ventricular tachyarrhythmia by programmed electrophysiologic testing were treated with intravenous magnesium. Following magnesium infusion, all patients still had inducible ventricular tachyarrhythmia. Moreover, magnesium therapy was not associated with significant changes in ventricular refractory period or in the morphology, cycle length, or hemodynamic response to induced ventricular tachycardia. These data suggest that intravenous magnesium has no significant electrophysiologic or antiarrhythmic effects in patients with life-threatening ventricular arrhythmia and inducible ventricular tachyarrhythmia.

Atrial pacing with two-dimensional echocardiography for evaluation of chest pain: comparison with thallium 201 scintigraphy.

Atrial pacing was performed with two-dimensional (2-D) echocardiography and thallium 201 scintigraphy in 40 men with stable chest pain. Coronary angiography showed significant (one or more lesions greater than or equal to 50%) coronary artery disease (CAD) in 36 patients and no or insignificant CAD in 4. Two dimensional echocardiography showed a left ventricular wall motion abnormality (WMA) either at rest or with pacing in 28 (78%) patients with CAD, with 17 (47%) showing a new or worsened WMA with pacing. A thallium scan showing abnormality (reversible or fixed perfusion defect) was seen in 26 (72%) patients with CAD; 18 (50%) had a reversible defect. In all, 34 of the 36 patients with CAD (94%) had a WMA, a perfusion defect, or both (specificity 50%). Occurrence of both a WMA and a perfusion defect in individual segments ranged from 10 of 25 patients with septal abnormalities to 0 of 12 with abnormalities of the lateral segment. Sensitivity of 2-D echocardiography for identifying CAD in specific vessels was 81% for the left anterior descending (LAD) artery, 30% for the right coronary artery, and 20% for the circumflex artery (both p less than .001 compared with the LAD artery). Corresponding sensitivities for thallium 201 imaging were 54% (p less than .05 compared with 2-D echocardiography), 27%, and 8% (both p less than .05 compared with the LAD artery). When combined with atrial pacing, 2-D echocardiography and thallium 201 perfusion imaging are of similar value for diagnosing the presence of CAD in patients with stable chest pain. Two-dimensional echocardiography is superior to thallium 201 imaging for identifying the presence of significant CAD in the LAD artery, but both tests are limited in their ability to detect lesions of the right coronary or circumflex arteries.

Heart disease in systemic sclerosis.

Primary cardiovascular manifestations of SSc include pericardial disease, myocardial disease, conduction abnormalities, and cardiac arrhythmias. Significant cardiac abnormalities are present in more than half of SSc patients at autopsy. As the frequency of subclinical cardiac involvement is now appreciated and noninvasive cardiac diagnostic modalities continue to improve, the ability to detect early asymptomatic involvement in SSc has improved. Two-dimensional echocardiography, radionucleotide imaging, and ambulatory ECG allow recurrent serial testing with virtually no morbidity. The current treatment of cardiac involvement in SSc is emperic and primarily directed at symptomatology. Large prospective randomized trials are needed to determine if preventive therapy is effective. With the advent of new immunological and cardiotropic agents and a better understanding of the primary disease process, our ability to alter the pathogenesis and final outcome of cardiac involvement in SSc should improve.

Natural history of potentially lethal ventricular arrhythmias in patients treated with long-term antiarrhythmic drug therapy.

To examine the natural history of long-term anti-arrhythmic therapy in patients with benign and potentially lethal ventricular premature complexes (VPCs), 28 patients with initial efficacy with moricizine (greater than 75% suppression of baseline mean VPCs/hr and greater than 90% suppression of repetitive VPCs) were prospectively followed for 1 to 56 (mean +/- standard deviation 25 +/- 17) months. Patients were examined during baseline placebo, anti-arrhythmic drug therapy and intermittent pulsed-placebo reexamination periods. The mean VPCs of all patients at baseline entry were 233 +/- 47 VPCs/hr, and after moricizine therapy 14 +/- 4 VPCs/hr. Follow-up demonstrated that antiarrhythmic efficacy decreased to 75% at 12 months and to 62% at 24 months. Loss of antiarrhythmic drug efficacy most commonly occurred as a "transient" event (10 patients [36%]), and efficacy was spontaneously reestablished without a change in antiarrhythmic therapy. In contrast, increased dose titration of moricizine was necessary to reestablish antiarrhythmic suppression efficacy in 4 patients (14%), and 4 patients (14%) lost antiarrhythmic drug responsiveness during follow-up. Spontaneous decrease in baseline VPCs resulted in discontinuation of antiarrhythmic therapy in 3 patients, and increase in baseline VPCs was associated with a loss of antiarrhythmic response in 2 patients. Late proarrhythmic effects (2 patients, 7%), delayed side effects necessitating drug withdrawal (6 patients, 21%) and medical events (4 patients, 14%) occurred during 56 months of follow-up. Individual serum moricizine levels remained in the therapeutic range throughout the study and did not correlate with changes in antiarrhythmic efficacy.(ABSTRACT TRUNCATED AT 250 WORDS)

The hemodynamic benefit of differential atrioventricular delay intervals for sensed and paced atrial events during physiologic pacing.

The ability to program different atrioventricular (AV) delay intervals for paced and sensed atrial events is incorporated in the design of some newer dual chamber pacemakers. However, little is known regarding the hemodynamic benefit of differential AV delay intervals or the magnitude of difference between optimal AV delay intervals for paced and sensed P waves in individual patients. In this study, Doppler-derived cardiac output was used to examine the optimal timing of paced and sensed atrial events in 24 patients with a permanent dual chamber pacemaker. The hemodynamic effect of utilizing separate optimal delay intervals for sensed and paced events compared with utilizing the same fixed AV delay interval for both was determined. The optimal delay interval during DVI (AV sequential) pacing and VDD (atrial triggered, ventricular inhibited) pacing at similar heart rates was 176 +/- 44 and 144 +/- 48 ms (p less than 0.002), respectively. The mean difference between the optimal AV delay intervals for sensed (VDD) and paced (DVI) P waves was 32 ms and was up to 100 ms in some individuals. The difference between optimal AV delay intervals for sensed and paced atrial events was similar in patients with complete heart block and those with intact AV node conduction. At the respective optimal AV delay intervals for sensed and paced P waves, there was no significant difference in the cardiac output during VDD compared with DVI pacing. However, cardiac output significant declined during VDD pacing at the optimal AV delay interval for a paced event and during DVI pacing at the optimal interval for a sensed event.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic benefit of atrioventricular synchrony: prediction from baseline Doppler-echocardiographic variables.

The purpose of this study was to determine if baseline Doppler-echocardiographic variables of systolic or diastolic function could predict the hemodynamic benefit of atrioventricular (AV) synchronous pacing. Twenty-four patients with a dual chamber pacemaker were studied. Baseline M-mode and two-dimensional echocardiograms were obtained and Doppler-echocardiographic measurements of mitral inflow and left ventricular outflow were made in VVI mode (single rate demand) and in VDD (atrial synchronous, ventricular inhibited) and DVI (AV sequentially paced) modes at AV intervals ranging from 50 to 300 ms. Forward stroke volume and cardiac output were determined in each mode at each AV interval from the left ventricular outflow tract flow velocities, and the percent increase in cardiac output over VVI mode was determined. M-mode measurements, including left ventricular end-diastolic dimension, shortening fraction and left atrial size and Doppler measurement of diastolic filling, including peak early velocity and percent atrial contribution, did not correlate with the percent increase in cardiac output during physiologic pacing. The stroke volume in VVI mode correlated significantly with the percent increase in cardiac output during physiologic pacing (r = -0.61, p less than 0.005 for VDD mode and r = -0.55, p less than 0.05 for DVI mode). Five of the 15 patients with VVI stroke volume less than 50 ml but none of the 9 patients with stroke volume greater than 50 ml had ventriculoatrial (VA) conduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Signal-averaged electrocardiography in the time and frequency domains.

The noninvasive signal-averaged electrocardiographic detection of late potentials correlates with the spontaneous occurrence of sustained ventricular tachycardia (VT). Frequency analysis of the electrocardiographic signal from the terminal QRS and ST segment also correlates with sustained VT. This study was designed to compare these 2 methods by analysis of signals recorded from the same hardware system. Signals were recorded from 234 patients with prior myocardial infarctions with a commercially available signal-averaging system. Patients were classified into 2 groups: group 1 consisted of 84 patients with VT and group 2 consisted of 150 patients without VT. In the frequency domain, magnitude and energy area ratios and peak ratios of the spectral plot from 20 to 50 Hz over 0 to 20 Hz were calculated for a 140-ms interval starting 60 ms after the beginning of the QRS. In the time domain, the duration of the filtered QRS was 121 +/- 29 ms for group 1 and 110 +/- 25 ms for group 2 (p less than 0.002). The duration of the terminal QRS less than 40 microV was 45 +/- 21 ms in group 1 and 36 +/- 18 ms in group 2 (p less than 0.001). The root-mean-square amplitude of the terminal 40 ms of the QRS was 25 +/- 24 microV in group 1 and 36 +/- 33 microV in group 2 (p less than 0.004).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ventricular function on the exercise hemodynamics of variable rate pacing.

To determine the effect of ventricular function on the exercise hemodynamics of variable rate pacing, 16 selected patients underwent paired, double-blind, randomized exercise tests in single rate demand (VVI) or variable rate (VVIR) pacing modes. Ejection fraction and cardiac index were determined by two-dimensional and Doppler echocardiography at baseline and during peak exercise. Baseline ejection fraction ranged from 14 to 73% and was less than 40% in 6 patients (Group 1) and greater than or equal to 40% in 10 patients (Group 2). Duration of exercise was longer during the VVIR mode (502 s) than during the VVI mode (449 s) (p less than 0.01) and unrelated to baseline ejection fraction. Heart rate during exercise increased 9% in the VVI mode and 35% in the VVIR mode (p less than 0.005). Cardiac index increased 49% in the VVI mode and 83% in the VVIR mode. Analysis of variance for repeated measures showed a significant effect of pacing mode (p less than 0.01) and exercise (p less than 0.001), but not baseline ejection fraction, on cardiac index. Baseline ejection fraction did not correlate with the increase in cardiac index in either pacing mode or with the difference in increase between modes. There was no significant difference between Groups 1 and 2 in exercise duration, peak heart rate-blood pressure (rate-pressure) product, baseline or peak heart rate or baseline or peak cardiac index. Therefore, in selected patients, VVIR pacing during exercise results in an increase in heart rate, duration of exercise and cardiac index that is unrelated to the degree of baseline left ventricular dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler echocardiographic assessment of the effect of varying atrioventricular delay and pacemaker mode on left ventricular filling.

Pulsed Doppler echocardiography was used to study the timing and dynamics of left ventricular filling in 14 patients with permanent dual-chamber programmable pacemakers. Pacemakers were programmed to atrial sensed (VDD) mode and atrial-ventricular sequential paced mode at low (DVI-L) and high (DVI-H) heart rates, and pulsed Doppler recordings of transmitral flow were analyzed at atrioventricular delays of 50 to 300 msec in each mode. There was a significant decrease in the one-third filling fraction in both VDD and DVI-L modes and a significant increase in DVI-H modes with increasing atrioventricular delay. The ratio of early filling area to atrial filling area was significantly lower at longer atrioventricular delays in both VDD and DVI-L modes. The time from pacemaker spike to mitral valve closure was highly significantly correlated with atrioventricular delay in VDD, DVI-L, and DVI-H modes (r = -0.92, p = 0.0001; r = -0.90, p = 0.0001; and r = -0.85, p = 0.0001, respectively) as was the diastolic filling time to a lesser extent (r = -0.73, p = 0.0001; r = -0.69, p = 0.0001; r = -0.61, p = 0.0001, respectively). Events reflecting atrial systole occurred at a later time in the cardiac cycle in the atrial paced vs the atrial sensed mode. Thus changes in atrioventricular delay and pacemaker mode in this group of patients are a strong determinant of the timing and dynamics of left ventricular filling.

Utility of ambulatory electrocardiography in detecting pacemaker dysfunction in the early postimplantation period.

The value of ambulatory electrocardiography (AECG) in detecting pacemaker dysfunction before hospital discharge was assessed in 100 patients a mean of 1.2 days after pacemaker implantation. The incidence of permanent pacemaker dysfunction detected by AECG in the early postimplantation period, the frequency that pacemaker dysfunction detected by AECG was not detected by telemetric monitoring and the frequency that results of AECG led to pacemaker reprogramming before hospital discharge were determined. AECG detected at least 1 type of pacemaker dysfunction in 35% of patients and routine telemetry identified the abnormality in only 8% (p less than 0.001). Pacemaker dysfunction occurred in 42% of patients with dual-chamber devices and 27% of those with single-chamber devices (difference not significant). In the 35 patients who had pacemaker malfunction, a total of 50 instances of pacemaker dysfunction were detected. Failure of atrial capture occurred in 2% of patients, failure of atrial sensing in 9%, failure of atrial output in 1%, failure of ventricular capture in 8%, failure of ventricular sensing in 14%, failure of ventricular output due to myopotential inhibition in 11% and pacemaker-mediated tachycardia in 5%. The results of the AECG led to a clinical intervention in 22 patients (pacemaker reprogramming in 21 patients and lead repositioning in 1 patient) in whom no pacemaker dysfunction was suspected on the basis of telemetry or clinical symptoms. In conclusion, AECG provides additional benefit beyond that of routine telemetry monitoring in identifying pacemaker dysfunction in the early period after implantation.