Repetitive ventricular response. Its incidence, inducibility, reproducibility, mechanism, and significance

Predictive value of various types of ventricular response to programmed ventricular stimulation: relation to Holter monitoring

The study was performed to determine the predictive value of programmed stimulation for identification of pts with ventricular arrhythmias: 75 patients were studied by means of 24-hour ambulatory ECG (24 ECG) and programmed right (in some patients also left) ventricle stimulation at sinus and two or three pacing rates using two (standard) and three extrastimuli or burst stimulation (extensive protocol). Lown classes 0, 1-3 and 4a-4b were observed in 24 ECG in 35, 14, and 26 patients, respectively. In programmed stimulation 1-6 repetitive ventricular responses (RVR) were found in 56 pts, nonsustained ventricular tachycardia in 11 and sustained ventricular tachycardia in 21 pts. High incidence of induced VT was found in pts with complex ventricular arrhythmia in 24 ECG, 81% of this group, in all but six pts only standard protocol was used. The 1-6 RVR were observed in almost 40% of pts without any arrhythmia.

CONCLUSION

Only VT induction is a useful index for high risk patients.

Long-term outcome following programmed electrical stimulation in patients with high-grade ventricular ectopy

To determine if programmed electrical stimulation (PES) could be utilized to identify patients with high-grade ventricular ectopy at low- or high-risk for sudden cardiac death, we performed PES in 40 patients with high-grade ventricular ectopy refractory to conventional antiarrhythmic agents. Twenty-one patients had a previous myocardial infarction, five had cardiomyopathy, six had hypertension, three had valvular heart disease and five had no known structural heart disease. The mean age was 50 years (range, 18 to 76). During programmed ventricular stimulation, eight patients had inducible sustained (more than 30 seconds) monomorphic ventricular tachycardia (Group I) but in 32 patients sustained ventricular tachycardia was not inducible (Group II). None of the five patients without structural heart disease were inducible while seven out of 21 (33%) patients with previous myocardial infarction had inducible ventricular tachycardia (VT). Antiarrhythmic therapy was instituted in patients with inducible VT; patients without inducible VT did not receive antiarrhythmic agents. In Group I, seven of the eight patients are alive (mean follow-up, 16 months) and in Group II, 28 of the 32 patients are alive (mean follow-up, 17 months). None of the five deaths were sudden. We conclude that in the absence of antiarrhythmic therapy, the incidence of sudden cardiac death is very low in patients with high-grade ventricular ectopy who do not have inducible monomorphic ventricular tachycardia during programmed ventricular stimulation.

Role of programmed electrical stimulation of the heart in risk stratification post-myocardial infarction

Programmed electrical stimulation (PES) of the heart was evaluated as a method of identifying patients at risk of sudden death post-myocardial infarction (post-MI). Eighty-four patients (mean age, 56 +/- 10 years) underwent PES 6 to 8 weeks post-MI. PES was performed at the right ventricular apex at twice diastolic threshold. Prior to stimulation patients were studied with exercise stress testing, 24-hour Holter monitoring and radionuclide ejection fraction. The patients were placed into two groups, according to their responses to electrical stimulation. Group 1:65 patients in whom no arrhythmias were induced or who had repetitive responses that lasted less than six cycles; Group 2:19 patients in whom ventricular tachycardia was induced. At the end of follow-up (20 +/- 9 months) six patients from Group 1 had died. Complex ventricular ectopy and ventricular tachycardia were more frequently detected on Holter in Group 2 (9/19) than in Group 1 (14/65) (p less than 0.03). The results of exercise testing and radionuclide ejection fraction did not correlate with the response to PES. However all but one of the patients who died had a left ventricular ejection fraction (LVEF) under 40% and four out of six patients had ventricular tachycardia on Holter monitor. We draw the conclusion that PES did not contribute to the identification of high-risk patients post-MI, as none of the 19 patients in whom ventricular tachycardia was induced died during follow-up. In addition, high-risk patients were characterized by poor ventricular function and complex ventricular arrhythmias on Holter recording.

Arrhythmias as predictors of sudden death

Two methods are available for exploring arrhythmias in cardiac patients who are at risk of sudden death: Holter monitoring and invasive electrophysiology. Despite numerous studies, the predictive value of these techniques, in terms of prognosis, remains poor for many reasons. Neither technique considered individually can give reliable prognostic indications simply because each technique addresses different issues which are only partially involved in the mechanism of sudden death. Invasive electrophysiology, by artificially provoking an arrhythmia, detects the potential substrate which may ultimately lead to lethal arrhythmias. Although this is an important technique it is insufficient because merely identifying the substrate for an arrhythmia does not necessarily mean that arrhythmia will occur. On the other hand, ambulatory ECG allows monitoring of spontaneous arrhythmias which may be considered as potential initiating factors in arrhythmias. However, even if initiating factors and potential substrates are present, they are not sufficient conditions to cause lethal arrhythmias to occur. When there is an opportunity to scrutinize the mechanism of arrhythmias which are indeed lethal, as in sudden death, it appears that the lethal event results from the intervention of a new factor which was either absent or not considered during preceding investigations. In coronary patients, curiously, ischemia more often provokes cardiac arrest or an electromechanical dissociation rather than a ventricular tachycardia or fibrillation. Sudden death is not infrequently of iatrogenic origin, because of the arrhythmogenic effect of powerful antiarrhythmic drugs. More important, ventricular fibrillation often occurs in the setting of a progressively increased sympathetic tone, which explains either the particular seriousness of a previously known arrhythmia or the occurrence of an arrhythmia which was never before observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Programmed ventricular stimulation in coronary artery disease and dilated cardiomyopathy: influence of the underlying heart disease on the results of electrophysiologic testing

In order to evaluate the clinical and prognostic significance of programmed ventricular stimulation (PVS), 100 patients were investigated. Twenty-four of 51 patients with coronary artery disease and 22 out of 49 with dilated cardiomyopathy had clinical ventricular tachycardia (VT). The study protocol included 24-h Holter ECG, cardiac catheterization and angiography, and PVS employing 1 and 2 premature extrastimuli and incremental pacing. In patients with coronary artery disease, VT was induced in 67% with prior VT and in 18% without such episodes (p less than 0.01). In dilated cardiomyopathy, however, patients with and without clinical VT did not differ with regard to VT inducibility (18% vs. 15%, NS). The inducibility of monomorphic sustained VT--most frequently induced in VT patients--was significantly higher in patients with coronary artery disease (p less than 0.05). Polymorphic nonsustained VT (in both coronary artery disease and dilated cardiomyopathy) was only initiated in patients without clinical VT. In patients with coronary artery disease, left ventricular ejection fraction could be correlated to clinical arrhythmia (p less than 0.001), while induced VT could only be correlated to depressed left ventricular function in patients with left ventricular aneurysm. Neither clinical nor induced VT could be correlated to left ventricular ejection fraction in patients with dilated cardiomyopathy. During a mean follow-up of 21 months, 7 patients died from sudden cardiac death. Six of them had clinical VT, but in only 1 patient with coronary artery disease was VT initiated. There was no apparent difference in the antiarrhythmic therapy of the patients with sudden death with respect to the surviving population. In conclusion, the response to PVS with the stimulation protocol applied is different in patients with coronary artery disease and dilated cardiomyopathy. The prognostic significance of the results obtained from PVS remains uncertain.

Pacing-induced angina pectoris and induction of ventricular arrhythmias in coronary artery disease

Ischemia caused by rapid pacing during electrophysiologic study could facilitate induction of ventricular arrhythmias. The results of extrastimulation were retrospectively analyzed in 32 patients with coronary artery disease (CAD) without a history of symptomatic arrhythmia. These patients were studied at cardiac catheterization for angina pectoris refractory to medical therapy. Eleven patients (group I) had typical angina during trains of rapid right ventricular pacing (repeated trains of 8 stimuli [mean cycle length (CL) 473 +/- 47 ms]) but were asymptomatic during slower trains (CL 800 +/- 100 ms). Twenty-one patients (group II) had no symptoms with either rapid (CL 448 +/- 51 ms) or slow (CL 688 +/- 105 ms) trains, despite comparable left ventricular function, CAD severity and medication. Effective refractory periods (S1S2) after rapid drive were shorter in group I than in group II patients (225 +/- 9 vs 240 +/- 14 ms, p less than 0.002), but refractory periods during slow pacing were similar (251 +/- 12 vs 253 +/- 17 ms, difference not significant). No patient in either group had sustained arrhythmia (more than 15 beats) induced by single and double ventricular extrastimuli, decrementally applied at the right ventricular apex. The number of extra beats provoked in group I when rapid trains caused angina (4.3 +/- 3.6) was similar to that induced by extra-stimulation after slower pacing without angina (4.4 +/- 3.5) and to that obtained with rapid or slow pacing in group II (3.1 +/- 3.3 and 2.8 +/- 2.2).(ABSTRACT TRUNCATED AT 250 WORDS)

Programmed ventricular stimulation in survivors of an acute myocardial infarction

The prognostic significance of programmed ventricular stimulation and its usefulness in relation to other forms of invasive and noninvasive testing was evaluated in 150 survivors of acute myocardial infarction. Ventricular tachyarrhythmias of 6 beats or more were induced in 35 (23%) patients. No significant differences existed between patients with inducible ventricular tachyarrhythmias and those without inducible ventricular tachycardia with respect to occurrence of spontaneous ventricular arrhythmias in the acute and early recovery phase of infarction or predischarge exercise-induced ischemia or arrhythmias, severity of coronary artery disease, or degree of left ventricular dysfunction. A higher incidence of inferior myocardial infarction was observed in patients with inducible ventricular tachycardia when compared with those without inducible ventricular tachycardia (66% vs 41%, p less than .01). During a mean follow-up of 10 +/- 5 months (range 2 to 19), there were two sudden deaths, three nonsudden deaths, and two additional patients developed sustained ventricular tachyarrhythmias. There was no significant difference between patients with and those without inducible ventricular tachyarrhythmias with respect to the occurrence of these events. In this study population, a lower mean ejection fraction (p less than .01), the presence of a ventricular aneurysm (p less than .05), and exercise-induced ventricular premature contractions (p less than .05) were predictors of sudden death and of spontaneous ventricular tachycardia. Thus, the findings of this study do not support the hypothesis that the induction of ventricular tachyarrhythmias in patients recovering from acute myocardial infarction identifies a group at high risk for sudden cardiac death.

Incidence and clinical significance of repetitive ventricular response in patients without identifiable organic heart disease

We determined the incidence of repetitive ventricular response (RVR) after programmed electrical stimulation and the incidence of spontaneous ventricular arrhythmias during 24 hr Holter monitoring in 38 patients in whom extensive non-invasive and invasive diagnostic tests had excluded abnormalities suggestive of organic heart disease. A standardized stimulation protocol with single (S1S2) and double (S1S2S3) extrastimuli during ventricular drive at cycle lengths of 600, 500 and 430 msec with a current strength below 5 mA at the right ventricular apex was employed. RVR occurred in 20 patients (58%) after S1S2 and in 30 patients (79%) after S1S2S3 stimulation. Eighteen patients (47%) showed RVR with 2 echo beats and 1 patient had 3 echo beats. RVR was due to bundle branch reentry (BBR) in 20 patients independent of the mode of stimulation. RVR due to intraventricular reentry (IVR) was found in 17 patients (47%) only after S1S2S3 stimulation. The incidence of both BBR and IVR was influenced by the basic ventricular driving rate, decreasing with shorter basic cycle lengths. 17 patients had no ventricular premature depolarizations (VPDs), 12 patients had uniform, 4 multiform (Lown III), 2 consecutive (Lown IVA) VPDs, and 1 patient had parasystolic rhythm. There was no relation to the incidence of repetitive ventricular response. We conclude that in patients without identifiable organic heart disease RVR with more than 2 consecutive beats is rarely found if single and double extrastimuli are employed during ventricular drive. Both bundle branch and intraventricular reentry with one or two echo beats are a common finding in this population without relation to the incidence of spontaneous ventricular arrhythmias.

Demonstration of reentry within the right bundle branch in man

Reentry within the right bundle branch which, to our knowledge is a hitherto undescribed mechanism of His-Purkinje reentry in man, was elicited during programmed right ventricular stimulation. Electrophysiologic analysis excluded atrioventricular nodal reentry. His bundle reentry, reentry involving both bundle branches, and intraventricular micro-reentry.

Programmed electrical stimulation in patients with high-grade ventricular ectopy: electrophysiologic findings and prognosis for survival

The significance and treatment of ventricular premature beats (VPBs) in patients without sustained ventricular tachycardia (VT), sudden death, or syncope remains unclear. We undertook a prospective study of programmed electrical stimulation (up to two extrastimuli and burst pacing) in 73 patients (age 60 +/- 10 years) with high-grade VPBs who had no evidence of sustained VT, sudden death, or syncope as determined by 48 hr of monitoring in the cardiac care unit and 48 hr Holter monitoring. Fifty-six patients (76.7%) had atherosclerotic heart disease, 10 (13.7%) had cardiomyopathy or valvular heart disease, and seven (9.6%) had no evident heart disease. Thirty-seven patients (50.7%) had Lown grade IVB VPBs, 30 (41.1%) had Lown grade IVA VPBs, and six (8.2%) had Lown grade III VPBs. Programmed electrical stimulation identified two groups of subjects: group 1 comprised 20 patients (27%) in whom VT or ventricular fibrillation was induced, group 2 comprised 53 patients (73%) in whom no ventricular arrhythmia or only two to four repetitive ventricular responses were induced. There was a significant difference between the presence of atherosclerotic heart disease, old myocardial infarction, and ejection fraction of less than 40% in group 1 compared with group 2. However, there was no significant difference in the grade of VPBs between the two groups. Seventeen of 20 patients from group 1 were placed on antiarrhythmic therapy (defined by programmed electrical stimulation), whereas group 2 patients were randomly assigned to prophylactic antiarrhythmic therapy. A total of 70 patients were followed up for 30 +/- 15 months. The incidence of sustained VT and/or sudden death (31.5% vs 2%; p less than .001) was significantly higher in group 1 compared with group 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Vulnerability of the right ventricle to cathodal, anodal, and bipolar stimulation at double diastolic threshold strength

The repetitive ventricular response (RVR) to three stimulation techniques (bipolar, cathodal and anodal) was investigated in 35 patients. 26 patients suffered from coronary heart disease and 9 patients from dilative cardiomyopathy. The stimulation study was performed at a ventricular driving rate of 120/min with one and two premature ventricular extrastimuli. We used rectangular impulses of 1.8 ms duration at double diastolic threshold strength. RVR was scored as follows: 0: no RVR, 1: one nonstimulated RVR, 2: two nonstimulated RVR, 3: three nonstimulated RVR, 4: four to ten nonstimulated RVR, 5: more than ten nonstimulated RVR lasting less than 2 minutes, 6: sustained ventricular tachycardia or ventricular fibrillation. We found that with unipolar anodal stimulation the diastolic threshold was significantly greater and the effective refractory period of the right ventricle was significantly shorter as compared to the other stimulation techniques. Between the three different electrode configurations there were no significant differences concerning the number of consecutive ventricular depolarizations following premature stimulation.

CONCLUSION

the phenomenon of RVR is not influenced by the stimulation technique (bipolar, cathodal and anodal) at double diastolic threshold.

Identifying patients at risk of sudden death after myocardial infarction: value of the response to programmed stimulation, degree of ventricular ectopic activity and severity of left ventricular dysfunction

The ability of programmed ventricular stimulation to identify risk of sudden death after acute myocardial infarction (MI) was compared with 24-hour electrocardiographic assessment of ventricular ectopic activity and determination of left ventricular (LV) dysfunction. Forty-six patients underwent programmed stimulation 8 to 60 days (mean 22) after documented MI. Programmed stimulation consisted of single and double extrastimuli from the right ventricular apex at 2 times diastolic threshold during ventricular pacing and normal sinus rhythm. Of the 46 patients, 44 underwent electrocardiographic monitoring at least 6 days after MI. In 43 of the 46 patients, LV ejection fraction (EF) and the presence of LV aneurysm were determined. In response to programmed ventricular stimulation, 5 patients had sustained ventricular tachycardia (VT), 5 had nonsustained VT (greater than or equal to 4 beats), 13 had intraventricular reentrant repetitive responses, and 23 had either bundle branch reentrant repetitive responses or no extra responses to programmed ventricular stimulation (negative study). During a mean follow-up of 18 months, 10 patients died, 6 suddenly. One of the 10 patients with sustained or nonsustained VT died suddenly, compared with 3 of 13 patients with intraventricular reentrant responses and 2 of 23 patients with a negative study (difference not significant). Of 25 patients with Grade 0 to 2 ventricular ectopic activity, 3 died suddenly after MI, compared with 3 of 19 patients with Grade 3 or 4 activity (difference not significant). By comparison, the frequency of sudden death was greater in patients with an LVEF of less than 40% (5 of 16 versus 1 of 27 patients) or an LV aneurysm (5 of 13 versus 1 of 30 patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Programmed electrical stimulation of the heart in coronary artery disease

The induction of ventricular arrhythmia in patients with a history of malignant ventricular arrhythmia by programmed electrical stimulation (PES) is associated with a poor prognosis. However, the incidence and significance of inducible arrhythmia in patients with stable coronary artery disease (CAD) who do not have a history of serious arrhythmia are unknown. We studied 32 such patients (31 men, mean age 55 years) with PES at the time of cardiac catheterization. Fourteen patients (Group I) manifested greater than or equal to 3 extraventricular responses when challenged with 1 to 3 propagated right ventricular extrastimuli during ventricular pacing. Twelve (86%) of these 14 had evidence of left ventricular dysfunction (LVD), defined by a global ejection fraction of less than 50% or regional wall motion abnormalities. The remaining 18 patients (Group II) manifested less than or equal to 2 responses to extrastimulation. Only 4 (22%) of these 18 had LVD. Proximal 3-vessel CAD was more frequent in Group I patients (10 of 14, 71%) than in Group II (7 of 18, 39%). Only 5 patients (4 from Group I and 1 from Group II) demonstrated complex arrhythmia during exercise testing or ambulatory monitoring. The induction of extraventricular responses during PES may serve as an independent marker of electrical instability in the coronary population and is a much more common finding in those with LVD.

Reduced human ventricular fibrillation threshold associated with contrast-induced Q-T prolongation

Injection of contrast dye during selective coronary arteriography prolongs the Q-T interval well beyond that expected for the accompanying bradycardia. A case is presented in which a 5 mA stimulus delivered prematurely by an improperly sensing ventricular demand pacemaker initiated ventricular fibrillation during coronary arteriography, although no evidence of coronary or other cardiac disease was found. An analysis is made of the progressive Q-T and T changes following contrast dye injection, and their relation to the onset of ventricular fibrillation. The implications of these observations are discussed in light of existing data on human ventricular vulnerability.

Prediction of sudden death by electrophysiologic studies in high risk patients surviving acute myocardial infarction

Seventy patients surviving a myocardial infarction complicated by heart failure or arrhythmias, or both, were studied 7 to 20 days after the infarction. Twenty-four hour electrocardiographic ambulatory monitoring and intracardiac electrophysiologic studies were performed in each patient. Electrophysiologic studies included introduction of single right ventricular premature stimuli during sinus rhythm (70 patients), atrial pacing (35 patients) and ventricular pacing (70 patients) at a stimulating voltage of 2 V, with the use of higher stimulating voltages (up to 10 V), and double right ventricular premature stimuli in 33 patients and pacing at a second right ventricular site in 50 patients. A repetitive response was defined as two or more spontaneous ventricular depolarizations in response to the premature stimuli, with His bundle reentry and aberrant conduction of supraventricular impulses excluded by a His bundle recording. Repetitive responses were initiated in 20 patients, and 12 patients had responses that were either sustained ventricular tachycardia or self-terminating ventricular tachycardia of more than five complexes in duration. The finding of a repetitive response was not related to the occurrence of complex ventricular arrhythmias during ambulatory monitoring or in the coronary care unit. Five of the 12 patients with sustained or self-terminating responses of more than five complexes died during the 12 month follow-up period, 4 suddenly, and these responses were significantly associated with late sudden death (p less than 0.05), because only 1 of 25 patients with responses of fewer than five complexes or no response to maximal provocation died suddenly. It is concluded that induced responses of more than five complexes in duration may be an important indicator of a potentially reversible risk of sudden death after myocardial infarction.